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diff --git a/old/12299-h/12299-h.htm b/old/12299-h/12299-h.htm new file mode 100644 index 0000000..58ff04d --- /dev/null +++ b/old/12299-h/12299-h.htm @@ -0,0 +1,9857 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> +<head> + <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> + <title>The Project Gutenberg eBook of The Mechanical Properties of Wood, +by Samuel J. Record, M.A., M.F.</title> + <style type="text/css"> + p { margin-top: .75em; + margin-left: 15%; + margin-right: 15%; + text-align: justify; + margin-bottom: .75em; + } + img { margin-left: auto; margin-right: auto; max-width: 100%; + } + table { margin-top: 2em; + margin-left: auto; + margin-right: auto; + margin-bottom: 2em; + } + tbody { text-align: center; + vertical-align: middle; + } + .ind { margin-left: 17%; + } + .ind2 { margin-left: 19%; + } + .ind3 { margin-left: 21%; + } + .imgtext { margin-top: .25em; + margin-left: 25%; + margin-right: 25%; + text-align: justify; + margin-bottom: 1em; + border-style: solid; + border-width: 1px; + border-color: #000000; + background-color: #ffffff; + } + .imgtitle { font-weight: bold; + margin-top: .25em; + margin-left: 45%; + margin-right: 45%; + text-align: center; margin-left: auto; margin-right: auto; + margin-bottom: .75em; + border-style: none; + border-width: 1px; + border-color: #ffffff; + background-color: #ffffff; + } +H1,H2,H3,H4,H5,H6 {text-align: center; margin-left: auto; margin-right: auto; + margin-left: 25%; + margin-right: 25%} + H1 { margin-top: 4em; } + H2 { margin-top: 3em; } + H3 { margin-top: 2em; } + li { margin-top: 0em; + margin-left: 25%; + margin-right: 25%; + text-align: left; + margin-bottom: 0em; + } + .hdr { margin-top: 2em; + margin-bottom: 2em; + } + .ctr { text-align: center + } + hr { width:50%; + margin-top: 1em; + margin-bottom: 1em; + } + </style> +</head> +<body> + + +<pre> + +Project Gutenberg's The Mechanical Properties of Wood, by Samuel J. Record + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Mechanical Properties of Wood + Including a Discussion of the Factors Affecting the Mechanical + Properties, and Methods of Timber Testing + + +Author: Samuel J. Record + +Release Date: May 8, 2004 [EBook #12299] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK THE MECHANICAL PROPERTIES OF WOOD *** + + + + +Produced by Curtis Weyant, GF Untermeyer and PG Distributed +Proofreaders. Scans provided by Case Western Reserve University's +Preservation Department http://www.cwru.edu/UL/preserve/general.htm + + + + + + +</pre> + + +<h1>THE MECHANICAL PROPERTIES OF WOOD</h1> + +<p class="ctr"><img src="images/fig00.jpg" alt="Frontispiece" id="fig00" /></p> +<p class="imgtitle">Frontispiece.</p> +<p class="imgtext">Photomicrograph of a small block of western hemlock. At the top +is the cross section showing to the right the late wood of one +season's growth, to the left the early wood of the next season. +The other two sections are longitudinal and show the fibrous +character of the wood. To the left is the radial section with +three rays crossing it. To the right is the tangential section +upon which the rays appear as vertical rows of beads. × 35. +<i>Photo by the author</i>.</p> + +<a name="BookTitle"></a><h2>THE MECHANICAL PROPERTIES OF WOOD</h2> + +<h4><i>Including a Discussion<br>of the Factors Affecting the Mechanical +Properties,<br>and Methods of Timber Testing</i></h4><br><br> + +<h4>BY</h4> +<h3>SAMUEL J. RECORD, M.A., M.F.</h3> +<h4>ASSISTANT PROFESSOR OF FOREST PRODUCTS, YALE UNIVERSITY</h4><br><br> + +<h4>FIRST EDITION<br>FIRST THOUSAND<br>1914</h4><br><br> + +<h3>BY THE SAME AUTHOR</h3> +<h4>Identification of the Economic Woods of the United States.<br> +8vo, vi + 117 pages, 15 figures. Cloth, $1.25 net.</h4><br><br> + +<h3>TO THE STAFF OF THE +<br>FOREST PRODUCTS LABORATORY, AT MADISON, WISCONSIN +<br>IN APPRECIATION OF THE MANY OPPORTUNITIES +<br>AFFORDED AND COURTESIES EXTENDED +<br>THE AUTHOR</h3><br><br> + +<a name="PREFACE"></a> +<h2>PREFACE</h2> + +<p>This book was written primarily for students of forestry to whom +a knowledge of the technical properties of wood is essential. +The mechanics involved is reduced to the simplest terms and +without reference to higher mathematics, with which the students +rarely are familiar. The intention throughout has been to avoid +all unnecessarily technical language and descriptions, thereby +making the subject-matter readily available to every one +interested in wood.</p> + +<p>Part I is devoted to a discussion of the mechanical properties +of wood—the relation of wood material to stresses and strains. +Much of the subject-matter is merely elementary mechanics of +materials in general, though written with reference to wood in +particular. Numerous tables are included, showing the various +strength values of many of the more important American woods.</p> + +<p>Part II deals with the factors affecting the mechanical +properties of wood. This is a subject of interest to all who are +concerned in the rational use of wood, and to the forester it +also, by retrospection, suggests ways and means of regulating +his forest product through control of the conditions of +production. Attempt has been made, in the light of all data at +hand, to answer many moot questions, such as the effect on the +quality of wood of rate of growth, season of cutting, heartwood +and sapwood, locality of growth, weight, water content, +steaming, and defects.</p> + +<p>Part III describes methods of timber testing. They are for the +most part those followed by the U.S. Forest Service. In schools +equipped with the necessary machinery the instructions will +serve to direct the tests; in others a study of the text with +reference to the illustrations should give an adequate +conception of the methods employed in this most important line +of research.</p> + +<p>The appendix contains a copy of the working plan followed by the +U.S. Forest Service in the extensive investigations covering the +mechanical properties of the woods grown in the United States. +It contains many valuable suggestions for the independent +investigator. In addition four tables of strength values for +structural timbers, both green and air-seasoned, are included. +The relation of the stresses developed in different structural +forms to those developed in the small clear specimens is given.</p> + +<p>In the bibliography attempt was made to list all of the +important publications and articles on the mechanical properties +of wood, and timber testing. While admittedly incomplete, it +should prove of assistance to the student who desires a fuller +knowledge of the subject than is presented here.</p> + +<p>The writer is indebted to the U.S. Forest Service for nearly all +of his tables and photographs as well as many of the data upon +which the book is based, since only the Government is able to +conduct the extensive investigations essential to a thorough +understanding of the subject. More than eighty thousand tests +have been made at the Madison laboratory alone, and the work is +far from completion.</p> + +<p>The writer also acknowledges his indebtedness to Mr. Emanuel +Fritz, M.E., M.F., for many helpful suggestions in the +preparation of Part I; and especially to Mr. Harry Donald +Tiemann, M.E., M.F., engineer in charge of Timber Physics at the +Government Forest Products Laboratory, Madison, Wisconsin, for +careful revision of the entire manuscript.</p> + +<p>SAMUEL J. RECORD.</p> + +<p>YALE FOREST SCHOOL, <i>July 1, 1914.</i></p> + +<a name="CONTENTS"></a> +<h2>CONTENTS</h2> + +<ul style="list-style-type: none"> +<li class="hdr"><a href="#PREFACE"><big>PREFACE</big></a></li> + +<li class="hdr"><a href="#PART_I"><big>PART I<br>THE MECHANICAL PROPERTIES OF WOOD</big></a></li> + +<li><a href="#I_01">Introduction</a></li> +<li><a href="#I_02">Fundamental considerations and definitions</a></li> +<li><a href="#I_03">Tensile strength</a></li> +<li><a href="#I_04">Compressive or crushing strength</a></li> +<li><a href="#I_05">Shearing strength</a></li> +<li><a href="#I_06">Transverse or bending strength: Beams</a></li> +<li><a href="#I_07">Toughness: Torsion</a></li> +<li><a href="#I_08">Hardness</a></li> +<li><a href="#I_09">Cleavability</a></li> + +<li class="hdr"><a href="#PART_II"><big>PART II<br>FACTORS AFFECTING THE MECHANICAL PROPERTIES OF WOOD</big></a></li> + +<li><a href="#II_01">Introduction</a></li> +<li><a href="#II_02">Rate of growth</a></li> +<li><a href="#II_03">Heartwood and sapwood</a></li> +<li><a href="#II_04">Weight, density, and specific gravity</a></li> +<li><a href="#II_05">Color</a></li> +<li><a href="#II_06">Cross grain</a></li> +<li><a href="#II_07">Knots</a></li> +<li><a href="#II_08">Frost splits</a></li> +<li><a href="#II_09">Shakes, galls, pitch pockets</a></li> +<li><a href="#II_10">Insect injuries</a></li> +<li><a href="#II_11">Marine wood-borer injuries</a></li> +<li><a href="#II_12">Fungous injuries</a></li> +<li><a href="#II_13">Parasitic plant injuries</a></li> +<li><a href="#II_14">Locality of growth</a></li> +<li><a href="#II_15">Season of cutting</a></li> +<li><a href="#II_16">Water content</a></li> +<li><a href="#II_17">Temperature</a></li> +<li><a href="#II_18">Preservatives</a></li> + +<li class="hdr"><a href="#PART_III"><big>PART III<br>TIMBER TESTING</big></a></li> + +<li><a href="#III_01">Working plan</a></li> +<li><a href="#III_02">Forms of material tested</a></li> +<li><a href="#III_03">Size of test specimens</a></li> +<li><a href="#III_04">Moisture determination</a></li> +<li><a href="#III_05">Machine for static tests</a></li> +<li><a href="#III_06">Speed of testing machine</a></li> +<li><a href="#III_07">Bending large beams</a></li> +<li><a href="#III_08">Bending small beams</a></li> +<li><a href="#III_09">Endwise compression</a></li> +<li><a href="#III_10">Compression across the grain</a></li> +<li><a href="#III_11">Shear along the grain</a></li> +<li><a href="#III_12">Impact test</a></li> +<li><a href="#III_13">Hardness test: Abrasion and indentation</a></li> +<li><a href="#III_14">Cleavage test</a></li> +<li><a href="#III_15">Tension test parallel to the grain</a></li> +<li><a href="#III_16">Tension test at right angles to the grain</a></li> +<li><a href="#III_17">Torsion test</a></li> +<li><a href="#III_18">Special tests</a></li> +<li><a href="#III_19">Spike pulling test</a></li> +<li><a href="#III_20">Packing boxes</a></li> +<li><a href="#III_21">Vehicle and implement woods</a></li> +<li><a href="#III_22">Cross-arms</a></li> +<li><a href="#III_23">Other tests</a></li> + +<li class="hdr"><a href="#APPENDIX"><big>APPENDIX</big></a></li> + +<li><a href="#APPENDIX_1">Sample working plan of United States Forest Service</a></li> +<li><a href="#APPENDIX_2">Strength values for structural timbers</a></li> + +<li class="hdr"><a href="#BIBLIOGRAPHY"><big>BIBLIOGRAPHY</big></a></li> + +<li><a href="#BIB_I">Part I: Some general works on mechanics, materials of construction, and testing of materials</a></li> +<li><a href="#BIB_II">Part II: Publications and articles on the mechanical properties of wood, and timber testing</a></li> +<li><a href="#BIB_III">Part III: Publications of the United States Government on the mechanical properties of wood, and timber testing</a></li> + +<li class="hdr"><big><b>ILLUSTRATIONS</b></big></li> + +<li><a href="#fig00"> Frontispiece. Photomicrograph of a small block of western hemlock </a></li> +<li><a href="#fig01">1. Stress-strain diagrams of two longleaf pine beams </a></li> +<li><a href="#fig02">2. Compression across the grain </a></li> +<li><a href="#fig03">3. Side view of failures in compression across the grain </a></li> +<li><a href="#fig04">4. End view of failures in compression across the grain </a></li> +<li><a href="#fig05">5. Testing a buggy-spoke in endwise compression </a></li> +<li><a href="#fig06">6. Unequal distribution of stress in a long column due to lateral bending </a></li> +<li><a href="#fig07">7. Endwise compression of a short column </a></li> +<li><a href="#fig08">8. Failures of a short column of green spruce </a></li> +<li><a href="#fig09">9. Failures of short columns of dry chestnut </a></li> +<li><a href="#fig10">10. Example of shear along the grain </a></li> +<li><a href="#fig11">11. Failures of test specimens in shear along the grain </a></li> +<li><a href="#fig12">12. Horizontal shear in a beam </a></li> +<li><a href="#fig13">13. Oblique shear in a short column </a></li> +<li><a href="#fig14">14. Failure of a short column by oblique shear </a></li> +<li><a href="#fig15">15. Diagram of a simple beam </a></li> +<li><a href="#fig16">16. Three common forms of beams—(1) simple, (2) cantilever, (3) continuous </a></li> +<li><a href="#fig17">17. Characteristic failures of simple beams </a></li> +<li><a href="#fig18">18. Failure of a large beam by horizontal shear </a></li> +<li><a href="#fig19">19. Torsion of a shaft </a></li> +<li><a href="#fig20">20. Effect of torsion on different grades of hickory </a></li> +<li><a href="#fig21">21. Cleavage of highly elastic wood </a></li> +<li><a href="#fig22">22. Cross-sections of white ash, red gum, and eastern hemlock </a></li> +<li><a href="#fig23">23. Cross-section of longleaf pine </a></li> +<li><a href="#fig24">24. Relation of the moisture content to the various strength values of spruce </a></li> +<li><a href="#fig25">25. Cross-section of the wood of western larch showing fissures in the thick-walled cells of the late wood </a></li> +<li><a href="#fig26">26. Progress of drying throughout the length of a chestnut beam </a></li> +<li><a href="#fig27">27. Excessive season checking </a></li> +<li><a href="#fig28">28. Control of season checking by the use of S-irons </a></li> +<li><a href="#fig29">29. Static bending test on a large beam </a></li> +<li><a href="#fig30">30. Two methods of loading a beam </a></li> +<li><a href="#fig31">31. Static bending test on a small beam </a></li> +<li><a href="#fig32">32. Sample log sheet, giving full details of a transverse bending test on a small pine beam </a></li> +<li><a href="#fig33">33. Endwise compression test </a></li> +<li><a href="#fig34">34. Sample log sheet of an endwise compression test on a short pine column </a></li> +<li><a href="#fig35">35. Compression across the grain </a></li> +<li><a href="#fig36">36. Vertical section of shearing tool </a></li> +<li><a href="#fig37">37. Front view of shearing tool </a></li> +<li><a href="#fig38">38. Two forms of shear test specimens </a></li> +<li><a href="#fig39">39. Making a shearing test </a></li> +<li><a href="#fig40">40. Impact testing machine </a></li> +<li><a href="#fig41">41. Drum record of impact bending test </a></li> +<li><a href="#fig42">42. Abrasion machine for testing the wearing qualities of woods </a></li> +<li><a href="#fig43">43. Design of tool for testing the hardness of woods by indentation </a></li> +<li><a href="#fig44">44. Design of tool for cleavage test </a></li> +<li><a href="#fig45">45. Design of cleavage test specimen </a></li> +<li><a href="#fig46">46. Designs of tension test specimens used in United States </a></li> +<li><a href="#fig47">47. Design of tension test specimen used in New South Wales </a></li> +<li><a href="#fig48">48. Design of tool and specimen for testing tension at right angles to the grain </a></li> +<li><a href="#fig49">49. Making a torsion test on hickory </a></li> +<li><a href="#fig50">50. Method of cutting and marking test specimens </a></li> +<li><a href="#fig51">51. Diagram of specific gravity apparatus </a></li> + +<li class="hdr"><big><b>TABLES</b></big></li> + +<li><a href="#TABLE_01">I. Comparative strength of iron, steel, and wood</a></li> +<li><a href="#TABLE_02">II. Ratio of strength of wood in tension and in compression</a></li> +<li><a href="#TABLE_03">III. Right-angled tensile strength of small clear pieces of 25 woods in green condition</a></li> +<li><a href="#TABLE_04">IV. Results of compression tests across the grain on 51 woods in green condition, and comparison with white oak</a></li> +<li><a href="#TABLE_05">V. Relation of fibre stress at elastic limit in bending to the crushing strength of blocks cut therefrom in pounds per square inch</a></li> +<li><a href="#TABLE_06">VI. Results of endwise compression tests on small clear pieces of 40 woods in green condition</a></li> +<li><a href="#TABLE_07">VII. Shearing strength along the grain of small clear pieces of 41 woods in green condition</a></li> +<li><a href="#TABLE_08">VIII. Shearing strength across the grain of various American woods</a></li> +<li><a href="#TABLE_09">IX. Results of static bending tests on small clear beams of 49 woods in green condition</a></li> +<li><a href="#TABLE_10">X. Results of impact bending tests on small clear beams of 34 woods in green condition</a></li> +<li><a href="#TABLE_11">XI. Manner of first failure of large beams</a></li> +<li><a href="#TABLE_12">XII. Hardness of 32 woods in green condition, as indicated by the load required to imbed a 0.444-inch steel ball to one-half its diameter</a></li> +<li><a href="#TABLE_13">XIII. Cleavage strength of small clear pieces of 32 woods in green condition</a></li> +<li><a href="#TABLE_14">XIV. Specific gravity, and shrinkage of 51 American woods</a></li> +<li><a href="#TABLE_15">XV. Effect of drying on the mechanical properties of wood, shown in ratio of increase due to reducing moisture content from the green condition to kiln-dry</a></li> +<li><a href="#TABLE_16">XVI. Effect of steaming on the strength of green loblolly pine</a></li> +<li><a href="#TABLE_17">XVII. Speed-strength moduli, and relative increase in strength at rates of fibre strain increasing in geometric ratio</a></li> +<li><a href="#TABLE_18">XVIII. Results of bending tests on green structural timbers</a></li> +<li><a href="#TABLE_19">XIX. Results of compression and shear tests on green structural timbers</a></li> +<li><a href="#TABLE_20">XX. Results of bending tests on air-seasoned structural timbers</a></li> +<li><a href="#TABLE_21">XXI. Results of compression and shear tests on air-seasoned structural timbers</a></li> +<li><a href="#TABLE_22">XXII. Working unit stresses for structural timber expressed in pounds per square inch</a></li> + +<li class="hdr"><a href="#INDEX"><big>INDEX</big></a></li> + +<li class="hdr"><a href="#FOOTNOTES"><big>FOOTNOTES</big></a></li> +</ul> + +<a name="pg001"></a> +<a name="PART_I"></a> +<h2>PART I<br>THE MECHANICAL PROPERTIES OF WOOD</h2> + +<a name="I_01"></a> +<h3>INTRODUCTION</h3> + +<p>The mechanical properties of wood are its fitness and ability to +resist applied or external forces. By external force is meant +any force outside of a given piece of material which tends to +deform it in any manner. It is largely such properties that +determine the use of wood for structural and building purposes +and innumerable other uses of which furniture, vehicles, +implements, and tool handles are a few common examples.</p> + +<p>Knowledge of these properties is obtained through +experimentation either in the employment of the wood in practice +or by means of special testing apparatus in the laboratory. +Owing to the wide range of variation in wood it is necessary +that a great number of tests be made and that so far as possible +all disturbing factors be eliminated. For comparison of +different kinds or sizes a standard method of testing is +necessary and the values must be expressed in some defined +units. For these reasons laboratory experiments if properly +conducted have many advantages over any other method.</p> + +<p>One object of such investigation is to find unit values for +strength and stiffness, etc. These, because of the complex +structure of wood, cannot have a constant value which will be +exactly repeated in each test, even though no error be made. The +most that can be accomplished is to find average values, the +amount of variation above and below, and the laws which govern +the variation. On account of the great variability in strength +of different specimens of wood even from the same stick and +appearing to be alike, it is important to eliminate as far as +possible all extraneous factors liable to influence the results +of the tests.</p> + +<p>The mechanical properties of wood considered in this book are: +(1) stiffness and elasticity, (2) tensile strength, (3) +<a name="pg002"></a> +compressive or crushing strength, (4) shearing strength, (5) +transverse or bending strength, (6) toughness, (7) hardness, (8) +cleavability, (9) resilience. In connection with these, +associated properties of importance are briefly treated.</p> + +<p>In making use of figures indicating the strength or other +mechanical properties of wood for the purpose of comparing the +relative merits of different species, the fact should be borne +in mind that there is a considerable range in variability of +each individual material and that small differences, such as a +few hundred pounds in values of 10,000 pounds, cannot be +considered as a criterion of the quality of the timber. In +testing material of the same kind and grade, differences of 25 +per cent between individual specimens may be expected in +conifers and 50 per cent or even more in hardwoods. The figures +given in the tables should be taken as indications rather than +fixed values, and as applicable to a large number collectively +and not to individual pieces.</p> + +<a name="I_02"></a> +<h3>FUNDAMENTAL CONSIDERATIONS AND DEFINITIONS</h3> + +<p>Study of the mechanical properties of a material is concerned +mostly with its behavior in relation to stresses and strains, +and the factors affecting this behavior. A <b>stress</b> is a +distributed force and may be defined as the mutual action (1) of +one body upon another, or (2) of one part of a body upon another +part. In the first case the stress is <i>external</i>; in the other +<i>internal</i>. The same stress may be internal from one point of +view and external from another. An external force is always +balanced by the internal stresses when the body is in +equilibrium.</p> + +<p>If no external forces act upon a body its particles assume +certain relative positions, and it has what is called its +<i>natural shape and size</i>. If sufficient external force is +applied the natural shape and size will be changed. This +distortion or deformation of the material is known as the +<b>strain</b>. Every stress produces a corresponding strain, and +within a certain limit (see <i>elastic limit</i>, <a href="#pg005">page 5</a>) +the strain is directly +proportional to the stress producing it.<a name="fn01r"></a><a href="#fn01"><sup><small>1</small></sup></a> The same intensity +of stress, however, does not <a name="pg003"></a> produce the same strain in +different materials or in different qualities of the same +material. No strain would be produced in a perfectly rigid body, +but such is not known to exist.</p> + +<p>Stress is measured in pounds (or other unit of weight or force). +A <b>unit stress</b> is the stress on a unit of the sectional +area.</p> + +<center> +<table summary="text"> +<tbody> +<tr><td rowspan="3"><big><big><big><big>(</big></big></big></big></td><td><br></td> <td><br></td><td><i>P</i></td><td rowspan="3"><big><big><big><big>)</big></big></big></big></td></tr> +<tr> <td>Unit stress</td><td>=</td> <td>---</td></tr> +<tr> <td><br></td> <td><br></td><td><i>A</i></td></tr> +</tbody> +</table> +</center> + +<p>For instance, if a load (<i>P</i>) of one +hundred pounds is uniformly supported by a vertical post with a +cross-sectional area (<i>A</i>) of ten square inches, the unit +compressive stress is ten pounds per square inch.</p> + +<p>Strain is measured in inches (or other linear unit). A <b>unit +strain</b> is the strain per unit of length. Thus if a post 10 +inches long before compression is 9.9 inches long under the +compressive stress, the total strain is 0.1 inch, and the unit +strain is</p> + +<center> +<table summary="text"> +<tbody> +<tr><td><i>l</i></td> <td><br></td> <td>0.1</td> <td><br></td><td><br></td></tr> +<tr> <td>---</td> <td>=</td> <td>-----</td><td>=</td> <td>0.01 inch per inch of length.</td></tr> +<tr><td><i>L</i></td> <td><br></td> <td>10</td> <td><br></td><td><br></td></tr> +</tbody> +</table> +</center> + +<p>As the stress increases there is a corresponding increase in the +strain. This ratio may be graphically shown by means of a +diagram or curve plotted with the increments of load or stress +as ordinates and the increments of strain as abscissæ. This is +known as the <b>stress-strain diagram</b>. Within the limit mentioned +above the diagram is a straight line. (<a href="#fig01">See Fig. 1</a>.) If the +results of similar experiments on different specimens are +plotted to the same scales, the diagrams furnish a ready means +for comparison. The greater the resistance a material offers to +deformation the steeper or nearer the vertical axis will be the +line.</p> + +<p class="ctr"><img src="images/fig01.jpg" alt="Figure 1" id="fig01" /></p> +<p class="imgtitle">Figure 1</p> +<p class="imgtext">Stress-strain diagrams of two longleaf +pine beams. E.L. = elastic limit. The areas of the triangles +0(EL)A and 0(EL)B represent the elastic resilience of the dry +and green beams, respectively.</p> + +<p>There are three kinds of internal stresses, namely, (1) +<b>tensile</b>, (2) <b>compressive</b>, and (3) <b>shearing</b>. When external +forces act upon a bar in a direction away from its ends or a +direct pull, the stress is a tensile stress; when toward the +ends or a direct push, compressive stress. In the first instance +the strain is an <i>elongation</i>; in the second a <i>shortening</i>. +Whenever the forces tend to cause one portion of the material to +slide upon another adjacent to it the action is called a +<i>shear</i>. The action is that of an ordinary pair of shears. When +riveted plates slide on each other the rivets are sheared off.</p> + +<a name="pg004"></a> + +<p>These three simple stresses may act together, producing compound +stresses, as in flexure. When a bow is bent there is a +compression of the fibres on the inner or concave side and an +elongation of the fibres on the outer or convex side. There is +also a tendency of the various fibres to slide past one another +in a longitudinal direction. If the bow were made of two or more +separate pieces of equal length it would be noted on bending +that slipping occurred along the surfaces of contact, and that +the ends would no longer be even. If these pieces were securely +glued together they would no longer slip, but the tendency to do +so would exist just the same. Moreover, it would be found in the +latter case that the bow would be much harder to bend than where +the pieces were not glued together—in other words, the +<i>stiffness</i> of the bow would be materially increased.</p> + +<a name="pg005"></a> + +<p><b>Stiffness</b> is the property by means of which a body acted upon +by external forces tends to retain its natural size and shape, +or resists deformation. Thus a material that is difficult to +bend or otherwise deform is stiff; one that is easily bent or +otherwise deformed is <i>flexible</i>. Flexibility is not the exact +counterpart of stiffness, as it also involves toughness and +pliability.</p> + +<p>If successively larger loads are applied to a body and then +removed it will be found that at first the body completely +regains its original form upon release from the stress—in other +words, the body is <b>elastic</b>. No substance known is perfectly +elastic, though many are practically so under small loads. +Eventually a point will be reached where the recovery of the +specimen is incomplete. This point is known as the <b>elastic +limit</b>, which may be defined as the limit beyond which it is +impossible to carry the distortion of a body without producing a +permanent alteration in shape. After this limit has been +exceeded, the size and shape of the specimen after removal of +the load will not be the same as before, and the difference or +amount of change is known as the <b>permanent set</b>.</p> + +<p>Elastic limit as measured in tests and used in design may be +defined as that unit stress at which the deformation begins to +increase in a faster ratio than the applied load. In practice +the elastic limit of a material under test is determined from +the stress-strain diagram. It is that point in the line where +the diagram begins perceptibly to curve.<a name="fn02r"></a><a href="#fn02"><sup><small>2</small></sup></a> <a href="#fig01">(See Fig. 1</a>.)</p> + +<p><b>Resilience</b> is the amount of work done upon a body in deforming +it. Within the elastic limit it is also a measure of the +potential energy stored in the material and represents the +amount of work the material would do upon being released from a +state of stress. This may be graphically represented by a +diagram in which the abscissæ represent the amount of deflection +and the ordinates the force acting. The area included between +the stress-strain curve and the initial line (which is zero) +represents the work done. (<a href="#fig01">See Fig. 1</a>.) If the unit of space is +in inches and the unit <a name="pg006"></a> of force is in pounds the result is +inch-pounds. If the elastic limit is taken as the apex of the +triangle the area of the triangle will represent the <b>elastic +resilience</b> of the specimen. This amount of work can be applied +repeatedly and is perhaps the best measure of the toughness of +the wood as a working quality, though it is not synonymous with +toughness.</p> + +<p>Permanent set is due to the <b>plasticity</b> of the material. A +perfectly plastic substance would have no elasticity and the +smallest forces would cause a set. Lead and moist clay are +nearly plastic and wood possesses this property to a greater or +less extent. The plasticity of wood is increased by wetting, +heating, and especially by steaming and boiling. Were it not for +this property it would be impossible to dry wood without +destroying completely its cohesion, due to the irregularity of +shrinkage.</p> + +<p>A substance that can undergo little change in shape without +breaking or rupturing is <b>brittle</b>. Chalk and glass are common +examples of brittle materials. Sometimes the word <i>brash</i> is +used to describe this condition in wood. A brittle wood breaks +suddenly with a clean instead of a splintery fracture and +without warning. Such woods are unfitted to resist shock or +sudden application of load.</p> + +<p>The measure of the stiffness of wood is termed the <b>modulus of +elasticity</b> (or <i>coefficient of elasticity</i>). It is the ratio of +stress per unit of area to the deformation per unit of +length.</p> + +<center> +<table summary="text"> +<tbody> +<tr><td rowspan="3"><big><big><big><big>(</big></big></big></big></td><td><br></td><td><br></td><td>unit stress</td><td rowspan="3"><big><big><big><big>)</big></big></big></big> </td></tr> +<tr> <td>E </td> <td>= </td> <td>------------- </td></tr> +<tr> <td><br></td><td><br></td><td>unit strain<br></td></tr> +</tbody> +</table> +</center> + +<p>It is a number indicative of +stiffness, not of strength, and only applies to conditions +within the elastic limit. It is nearly the same whether derived +from compression tests or from tension tests.</p> + +<p>A large modulus indicates a stiff material. Thus in green wood +tested in static bending it varies from 643,000 pounds per +square inch for arborvitæ to 1,662,000 pounds for longleaf pine, +and 1,769,000 pounds for pignut hickory. (<a href="#TABLE_09">See Table IX</a>.) The +values derived from tests of small beams of dry material are +much greater, approaching 3,000,000 for some of our woods. These +values are small when compared with steel which has a <a name="pg007"></a> modulus of +elasticity of about 30,000,000 pounds per square inch. (<a href="#TABLE_01">See Table I</a>.)</p> + +<center> +<table id="TABLE_01" summary="TABLE_I" border="3" cellspacing="0" cellpadding="1" width="60%"> +<tbody> +<tr><th colspan="6"> TABLE I </th></tr> +<tr><th colspan="6"> COMPARATIVE STRENGTH OF IRON, STEEL, AND WOOD </th></tr> +<tr><th rowspan="2"> MATERIAL </th> <th rowspan="2"> Sp. gr.,dry </th> + <th> Modulus of elasticity in bending </th> + <th> Tensile strength </th> + <th> Crushing strength </th> + <th> Modulus of rupture </th></tr> +<tr> <th><i>Lbs. per sq. in.</i></th> + <th><i>Lbs. per sq. in.</i></th> + <th><i>Lbs. per sq. in.</i></th> + <th><i>Lbs. per sq. in.</i></th></tr> +<tr><td style="text-align: left;"> Cast iron, cold blast (Hodgkinson)</td> <td> 7.1 </td><td> 17,270,000 </td><td> 16,700 </td><td> 106,000 </td><td> 38,500 </td></tr> +<tr><td style="text-align: left;"> Bessenger steel, high grade (Fairbain).</td><td> 7.8 </td><td> 29,215,000 </td><td> 88,400 </td><td> 225,600 </td><td><br></td></tr> +<tr><td style="text-align: left;"> Longleaf pine, 3.5% moisture (U.S.)</td> <td> .63 </td><td> 2,800,000 </td> <td><br></td> <td> 13,000 </td> <td> 21,000 </td></tr> +<tr><td style="text-align: left;"> Redspruce, 3.5% moisture (U.S.)</td> <td> .41 </td><td> 1,800,000 </td> <td><br></td> <td> 8,800 </td> <td> 14,500 </td></tr> +<tr><td style="text-align: left;"> Pignut hickory, 3.5% moisture (U.S.)</td> <td> .86 </td><td> 2,370,000 </td> <td><br></td> <td> 11,130 </td> <td> 24,000 </td></tr> +<tr><td style="text-align: left;" colspan="6"> NOTE.—Great variation may be found in different samples of metals as well as of wood. The examples given represent reasonable values. </td></tr> +</tbody> +</table> +</center> + +<a name="I_03"></a> +<h3>TENSILE STRENGTH</h3> + +<p><b>Tension</b> results when a pulling force is applied to opposite +ends of a body. This external pull is communicated to the +interior, so that any portion of the material exerts a pull or +tensile force upon the remainder, the ability to do so depending +upon the property of cohesion. The result is an elongation or +stretching of the material in the direction of the applied +force. The action is the opposite of compression.</p> + +<p>Wood exhibits its greatest strength in tension parallel to the +grain, and it is very uncommon in practice for a specimen to be +pulled in two lengthwise. This is due to the difficulty of +making the end fastenings secure enough for the full tensile +strength to be brought into play before the fastenings shear off +longitudinally. This is not the case with metals, and as a +result they are used in almost all places where tensile strength +is particularly needed, even though the remainder of the +structure, such as sills, beams, joists, posts, and flooring, +may be of wood. Thus in a wooden truss bridge the tension +members are steel rods.</p> + +<a name="pg008"></a> + +<p>The tensile strength of wood parallel to the grain depends upon +the strength of the fibres and is affected not only by the +nature and dimensions of the wood elements but also by their +arrangement. It is greatest in straight-grained specimens with +thick-walled fibres. Cross grain of any kind materially reduces +the tensile strength of wood, since the tensile strength at +right angles to the grain is only a small fraction of that +parallel to the grain.</p> + +<center> +<table id="TABLE_02" summary="TABLE_II" border="3" cellspacing="0" cellpadding="1" width="40%"> +<tbody> +<tr><th colspan="4"> TABLE II </th></tr> +<tr><th colspan="4"> RATIO OF STRENGTH OF WOOD IN TENSION AND IN COMPRESSION </th></tr> +<tr><td colspan="4"> (Bul. 10, U. S. Div. of Forestry, p. 44) </td></tr> +<tr><th rowspan="3"> KIND OF WOOD </th> <th rowspan="3"> Ratio:<br>R =<br>Tensile strength<br>---------------------<br>compressive strength </th> + <th colspan="2"> A stick 1 square inch in cross section.<br></th></tr> +<tr> <th colspan="2"> Weight required to— </th></tr> +<tr> <th> Pull apart</th> + <th> Crush endwise</th></tr> +<tr><td style="text-align: left;"> Hickory </td> <td> 3.7 </td><td> 32,000 </td><td> 8,500 </td></tr> +<tr><td style="text-align: left;"> Elm </td> <td> 3.8 </td><td> 29,000 </td><td> 7,500 </td></tr> +<tr><td style="text-align: left;"> Larch </td> <td> 2.3 </td><td> 19,400 </td><td> 8,600 </td></tr> +<tr><td style="text-align: left;"> Longleaf Pine </td><td> 2.2 </td><td> 17,300 </td><td> 7,400 </td></tr> +<tr><td style="text-align: left;" colspan="4"> NOTE.—Moisture condition not given. </td></tr> +</tbody> +</table> +</center> + +<p>Failure of wood in tension parallel to the grain occurs +sometimes in flexure, especially with dry material. The tension +portion of the fracture is nearly the same as though the piece +were pulled in two lengthwise. The fibre walls are torn across +obliquely and usually in a spiral direction. There is +practically no pulling apart of the fibres, that is, no +separation of the fibres along their walls, regardless of their +thickness. The nature of tension failure is apparently not +affected by the moisture condition of the specimen, at least not +so much so as the other strength values.<a name="fn03r"></a><a href="#fn03"><sup><small>3</small></sup></a></p> + +<p>Tension at right angles to the grain is closely related to +cleavability. When wood fails in this manner the thin fibre +walls are torn in two lengthwise while the thick-walled fibres +are usually pulled apart along the primary wall.</p> + +<a name="pg009"></a> + +<center> +<table id="TABLE_03" summary="TABLE_III" border="3" cellspacing="0" cellpadding="1" width="40%"> +<tbody> +<tr><th colspan="3"> TABLE III </th></tr> +<tr><th colspan="3"> TENSILE STRENGTH AT RIGHT ANGLES TO THE GRAIN OF SMALL CLEAR PIECES OF 25 WOODS IN GREEN CONDITION </th></tr> +<tr><td colspan="3"> (Forest Service Cir. 213)</td></tr> +<tr><th rowspan="2"> COMMON NAME OF SPECIES</th> <th> When surface of failure is radial </th> + <th> When surface of failure is tangential </th></tr> +<tr> <th><i>Lbs. per sq. inch</i></th> + <th><i>Lbs. per sq. inch</i></th></tr> +<tr><th> <i>Hardwoods </i></th> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Ash, white </td> <td> 645 </td> <td> 671 </td></tr> +<tr><td style="text-align: left;"> Basswood </td> <td> 226 </td> <td> 303 </td></tr> +<tr><td style="text-align: left;"> Beech </td> <td> 633 </td> <td> 969 </td></tr> +<tr><td style="text-align: left;"> Birch, yellow </td> <td> 446 </td> <td> 526 </td></tr> +<tr><td style="text-align: left;"> Elm, slippery </td> <td> 765 </td> <td> 832 </td></tr> +<tr><td style="text-align: left;"> Hackberry </td> <td> 661 </td> <td> 786 </td></tr> +<tr><td style="text-align: left;"> Locust, honey </td> <td> 1,133 </td><td> 1,445 </td></tr> +<tr><td style="text-align: left;"> Maple, sugar </td> <td> 610 </td> <td> 864 </td></tr> +<tr><td style="text-align: left;"> Oak, post </td> <td> 714 </td> <td> 924 </td></tr> +<tr><td style="text-align: left;"> red </td> <td> 639 </td> <td> 874 </td></tr> +<tr><td style="text-align: left;"> swamp white </td> <td> 757 </td> <td> 909 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 622 </td> <td> 749 </td></tr> +<tr><td style="text-align: left;"> yellow </td> <td> 728 </td> <td> 929 </td></tr> +<tr><td style="text-align: left;"> Sycamore </td> <td> 540 </td> <td> 781 </td></tr> +<tr><td style="text-align: left;"> Tupelo</td> <td> 472 </td> <td> 796 </td></tr> +<tr><th> <i>Conifers </i></th> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Arborvitæ </td> <td> 241 </td> <td> 235 </td></tr> +<tr><td style="text-align: left;"> Cypress, bald </td> <td> 242 </td> <td> 251 </td></tr> +<tr><td style="text-align: left;"> Fir, white </td> <td> 213 </td> <td> 304 </td></tr> +<tr><td style="text-align: left;"> Hemlock </td> <td> 271 </td> <td> 323 </td></tr> +<tr><td style="text-align: left;"> Pine, longleaf </td> <td> 240 </td> <td> 298 </td></tr> +<tr><td style="text-align: left;"> red </td> <td> 179 </td> <td> 205 </td></tr> +<tr><td style="text-align: left;"> sugar </td> <td> 239 </td> <td> 304 </td></tr> +<tr><td style="text-align: left;"> western yellow </td><td> 230 </td> <td> 252 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 225 </td> <td> 285 </td></tr> +<tr><td style="text-align: left;"> Tamarack </td> <td> 236 </td> <td> 274 </td></tr> +</tbody> +</table> +</center> + +<a name="I_04"></a> +<h3>COMPRESSIVE OR CRUSHING STRENGTH</h3> + +<p><b>Compression across the grain</b> is very closely related to +hardness and transverse shear. There are two ways in which wood +is subjected to stress of this kind, namely, (1) with the load +acting over the entire area of the specimen, and (2) with a load +concentrated over a portion of the area. (<a href="#fig02">See Fig. 2</a>.) The +latter is the condition more commonly met with in practice, as, +for example, where a post rests on a horizontal sill, or a rail +rests on a cross-tie. The former condition, however, gives the +true resistance of the grain to simple crushing.]</p> + +<p class="ctr"><img src="images/fig02.jpg" alt="Figure 2" id="fig02" /></p> +<p class="imgtitle">Figure 2</p> +<p class="imgtext">Compression across the grain.</p> + +<a name="pg010"></a> + +<p>The first effect of compression across the grain is to compact +the fibres, the load gradually but irregularly increasing as the +density of the material is increased. If the specimen lies on a +flat surface and the load is applied to only a portion of the +upper area, the bearing plate indents the wood, crushing the +upper fibres without affecting the lower part. (<a href="#fig03">See Fig. 3</a>.) As +the load increases the projecting ends sometimes split +horizontally. (<a href="#fig04">See Fig. 4</a>.) The irregularities in the load are +due to the fact that the fibres collapse a few at a time, +beginning with those with the thinnest walls. The projection <a name="pg012"></a> of +the ends increases the strength of the material directly beneath +the compressing weight by introducing a beam action which helps +support the load. This influence is exerted for a short distance +only.</p> + +<p class="ctr"><img src="images/fig03.jpg" alt="Figure 3" id="fig03" /></p> +<p class="imgtitle">Figure 3</p> +<p class="imgtext">Side view of failures in compression +across the grain, showing crushing of blocks under bearing +plate. Specimen at right shows splitting at ends.</p> + +<p class="ctr"><img src="images/fig04.jpg" alt="Figure 4" id="fig04" /></p> +<p class="imgtitle">Figure 4</p> +<p class="imgtext">End view of failures in compression +across the grain, showing splitting of the ends of the test +specimens.</p> + +<a name="pg013"></a> + +<center> +<table id="TABLE_04" summary="TABLE_IV" border="3" cellspacing="0" cellpadding="1" width="40%"> +<tbody> +<tr><th colspan="3"> TABLE IV </th></tr> +<tr><th colspan="3"> RESULTS OF COMPRESSION TESTS ACROSS THE GRAIN ON 51 WOODS IN GREEN CONDITION, AND COMPARISON WITH WHITE OAK </th></tr> +<tr><th colspan="3"> (U. S. Forest Service) </th></tr> +<tr><th rowspan="2"> COMMON NAME OF SPECIES </th> + <th> Fibre stress at elastic limit perpendicular to grain </th> + <th> Fiber stress in per cent of white oak, or 853 pounds per sq. in. </th></tr> +<tr> <th><i>Lbs. per sq. inch</i></th> + <th><i>Per cent</i></th></tr> +<tr><td style="text-align: left;"> Osage orange </td> <td> 2,260 </td><td> 265.0 </td></tr> +<tr><td style="text-align: left;"> Honey locust </td> <td> 1,684 </td><td> 197.5 </td></tr> +<tr><td style="text-align: left;"> Black locust </td> <td> 1,426 </td><td> 167.2 </td></tr> +<tr><td style="text-align: left;"> Post oak </td> <td> 1,148 </td><td> 134.6 </td></tr> +<tr><td style="text-align: left;"> Pignut hickory </td> <td> 1,142 </td><td> 133.9 </td></tr> +<tr><td style="text-align: left;"> Water hickory </td> <td> 1,088 </td><td> 127.5 </td></tr> +<tr><td style="text-align: left;"> Shagbark hickory </td> <td> 1,070 </td><td> 125.5 </td></tr> +<tr><td style="text-align: left;"> Mockernut hickory </td> <td> 1,012 </td><td> 118.6 </td></tr> +<tr><td style="text-align: left;"> Big shellbark hickory </td><td> 997 </td> <td> 116.9 </td></tr> +<tr><td style="text-align: left;"> Bitternut hickory </td> <td> 986 </td> <td> 115.7 </td></tr> +<tr><td style="text-align: left;"> Nutmeg hickory </td> <td> 938 </td> <td> 110.0 </td></tr> +<tr><td style="text-align: left;"> Yellow oak </td> <td> 857 </td> <td> 100.5 </td></tr> +<tr><td style="text-align: left;"> White oak </td> <td> 853 </td> <td> 100.0 </td></tr> +<tr><td style="text-align: left;"> Bur oak </td> <td> 836 </td> <td> 98.0 </td></tr> +<tr><td style="text-align: left;"> White ash </td> <td> 828 </td> <td> 97.1 </td></tr> +<tr><td style="text-align: left;"> Red oak </td> <td> 778 </td> <td> 91.2 </td></tr> +<tr><td style="text-align: left;"> Sugar maple </td> <td> 742 </td> <td> 87.0 </td></tr> +<tr><td style="text-align: left;"> Rock elm </td> <td> 696 </td> <td> 81.6 </td></tr> +<tr><td style="text-align: left;"> Beech </td> <td> 607 </td> <td> 71.2 </td></tr> +<tr><td style="text-align: left;"> Slippery elm </td> <td> 599 </td> <td> 70.2 </td></tr> +<tr><td style="text-align: left;"> Redwood </td> <td> 578 </td> <td> 67.8 </td></tr> +<tr><td style="text-align: left;"> Bald cypress </td> <td> 548 </td> <td> 64.3 </td></tr> +<tr><td style="text-align: left;"> Red maple </td> <td> 531 </td> <td> 62.3 </td></tr> +<tr><td style="text-align: left;"> Hackberry </td> <td> 525 </td> <td> 61.6 </td></tr> +<tr><td style="text-align: left;"> Incense cedar </td> <td> 518 </td> <td> 60.8 </td></tr> +<tr><td style="text-align: left;"> Hemlock </td> <td> 497 </td> <td> 58.3 </td></tr> +<tr><td style="text-align: left;"> Longleaf pine </td> <td> 491 </td> <td> 57.6 </td></tr> +<tr><td style="text-align: left;"> Tamarack </td> <td> 480 </td> <td> 56.3 </td></tr> +<tr><td style="text-align: left;"> Silver maple </td> <td> 456 </td> <td> 53.5 </td></tr> +<tr><td style="text-align: left;"> Yellow birch </td> <td> 454 </td> <td> 53.2 </td></tr> +<tr><td style="text-align: left;"> Tupelo </td> <td> 451 </td> <td> 52.9 </td></tr> +<tr><td style="text-align: left;"> Black cherry </td> <td> 444 </td> <td> 52.1 </td></tr> +<tr><td style="text-align: left;"> Sycamore </td> <td> 433 </td> <td> 50.8 </td></tr> +<tr><td style="text-align: left;"> Douglas fir </td> <td> 427 </td> <td> 50.1 </td></tr> +<tr><td style="text-align: left;"> Cucumber tree </td> <td> 408 </td> <td> 47.8 </td></tr> +<tr><td style="text-align: left;"> Shortleaf pine </td> <td> 400 </td> <td> 46.9 </td></tr> +<tr><td style="text-align: left;"> Red pine </td> <td> 358 </td> <td> 42.0 </td></tr> +<tr><td style="text-align: left;"> Sugar pine </td> <td> 353 </td> <td> 41.1 </td></tr> +<tr><td style="text-align: left;"> White elm</td> <td> 351 </td> <td> 41.2 </td></tr> +<tr><td style="text-align: left;"> Western yellow pine </td> <td> 348 </td> <td> 40.8 </td></tr> +<tr><td style="text-align: left;"> Lodgepole pine </td> <td> 348 </td> <td> 40.8 </td></tr> +<tr><td style="text-align: left;"> Red spruce </td> <td> 345 </td> <td> 40.5 </td></tr> +<tr><td style="text-align: left;"> White pine </td> <td> 314 </td> <td> 36.8 </td></tr> +<tr><td style="text-align: left;"> Engelman spruce </td> <td> 290 </td> <td> 34.0 </td></tr> +<tr><td style="text-align: left;"> Arborvitæ </td> <td> 288 </td> <td> 33.8 </td></tr> +<tr><td style="text-align: left;"> Largetooth aspen </td> <td> 269 </td> <td> 31.5 </td></tr> +<tr><td style="text-align: left;"> White spruce </td> <td> 262 </td> <td> 30.7 </td></tr> +<tr><td style="text-align: left;"> Butternut </td> <td> 258 </td> <td> 30.3 </td></tr> +<tr><td style="text-align: left;"> Buckeye (yellow) </td> <td> 210 </td> <td> 24.6 </td></tr> +<tr><td style="text-align: left;"> Basswood </td> <td> 209 </td> <td> 24.5 </td></tr> +<tr><td style="text-align: left;"> Black willow </td> <td> 193 </td> <td> 22.6 </td></tr> +</tbody> +</table> +</center> + +<p>When wood is used for columns, props, posts, and spokes, the +weight of the load tends to shorten the material endwise. This +is <b>endwise compression</b>, or compression parallel to the grain. +In the case of long columns, that is, pieces in which the length +is very great compared with their diameter, the failure is by +sidewise bending or flexure, instead of by crushing or +splitting. (<a href="#fig05">See Fig. 5</a>.) A familiar instance of this action is +afforded by a flexible walking-stick. If downward pressure is +exerted with the hand on the upper end of the stick placed +vertically on the floor, it will be noted that a definite amount +of force must be applied in each instance before decided flexure +takes place. After this point is reached a very slight increase +of pressure very largely increases the deflection, thus +obtaining so great a leverage about the middle section as to +cause rupture.</p> + +<a name="pg011"></a> + +<p class="ctr"><img src="images/fig05.jpg" alt="Figure 5" id="fig05" /></p> +<p class="imgtitle">Figure 5</p> +<p class="imgtext"> Testing a buggy spoke in endwise +compression, illustrating the failure by sidewise bending of a +long column fixed only at the lower end. <i>Photo by U. S. Forest +Service</i></p> + +<p>The lateral bending of a column produces a combination of +bending with compressive stress over the section, the +compressive stress being maximum at the section of greatest +deflection on the concave side. The convex surface is under +tension, as in an ordinary beam test. (<a href="#fig06">See Fig. 6</a>.) If the same +stick is braced in such a way that flexure is prevented, its +supporting strength is increased enormously, since the +compressive stress acts uniformly over the section, and failure +is by crushing or splitting, as in small blocks. In all columns +free to bend in any direction the deflection will be seen in the +direction in which the column is least stiff. This sidewise +bending can be overcome by making pillars and columns thicker in +the middle than at the ends, and by bracing studding, props, and +compression <a name="pg014"></a> members of trusses. The strength of a column also +depends to a considerable extent upon whether the ends are free +to turn or are fixed.</p> + +<p class="ctr"><img src="images/fig06.jpg" alt="Figure 6" id="fig06" /></p> +<p class="imgtitle">Figure 6</p> +<p class="imgtext"> Unequal distribution of stress in a long +column due to lateral bending.</p> + +<p>The complexity of the computations depends upon the way in which +the stress is applied and the manner in which the stick bends. +Ordinarily where the length of the test specimen is not greater +than four diameters and the ends are squarely faced (<a href="#fig07">See Fig. 7</a>.), +the force acts uniformly over each square inch of area and +the crushing strength is equal to the maximum load (<i>P</i>) divided +by the area of the cross-section (<i>A</i>).</p> + +<center> +<table summary="text"> +<tbody> +<tr><td rowspan="3"><big><big><big><big>(</big></big></big></big></td><td><br></td> <td><br></td><td><i>P</i></td><td rowspan="3"><big><big><big><big>)</big></big></big></big></td></tr> +<tr> <td><i>C</i></td><td>=</td> <td>---</td></tr> +<tr> <td><br></td> <td><br></td><td><i>A</i></td></tr> +</tbody> +</table> +</center> + +<p class="ctr"><img src="images/fig07.jpg" alt="Figure 7" id="fig07" /></p> +<p class="imgtitle">Figure 7</p> +<p class="imgtext"> Endwise compression of a short column.</p> + +<p>It has been demonstrated<a name="fn04r"></a><a href="#fn04"><sup><small>4</small></sup></a> that the ultimate strength in +compression parallel to the grain is very nearly the same as the +extreme <a name="pg015"></a> fibre stress at the elastic limit in bending. (<a href="#TABLE_05">See Table 5</a>.) +In other words, the transverse strength of beams at elastic +limit is practically equal to the compressive strength of the +same material in short columns. It is accordingly possible to +calculate the approximate breaking strength of beams from the +compressive strength of short columns except when the wood is +brittle. Since tests on endwise compression are simpler, easier +to make, and less expensive than transverse bending tests, the +importance of this relation is obvious, though it does not do +away with the necessity of making beam tests.</p> + +<center> +<table id="TABLE_05" summary="TABLE_V" border="3" cellspacing="0" cellpadding="1" width="60%"> +<tbody> +<tr><th colspan="7"> TABLE V </th></tr> +<tr><th colspan="7"> RELATION OF FIBRE STRESS AT ELASTIC LIMIT (<i>r</i>) IN BENDING TO THE CRUSHING STRENGTH (<i>C</i>) OF BLOCKS CUT THEREFROM, IN POUNDS PER SQUARE INCH </th></tr> +<tr><td colspan="7"> (Forest Service Bul. 70, p. 90) </td></tr> +<tr><th colspan="7"> LONGLEAF PINE </th></tr> +<tr><th> MOISTURE CONDITION </th> <th> Soaked 50 per cent </th><th> Green 23 per cent </th> <th> 14 per cent </th> <th> 11.5 per cent </th><th> 9.5 per cent </th><th> Kiln-dry 6.2 per cent </th></tr> +<tr><td> Number of tests averaged </td> <td> 5 </td> <td> 5 </td> <td> 5 </td> <td> 5 </td> <td> 4 </td> <td> 5 </td></tr> +<tr><td> <i>r</i> in bending </td> <td> 4,920 </td> <td> 5,944 </td> <td> 6,924 </td> <td> 7,852 </td> <td> 9,280 </td> <td> 11,550 </td></tr> +<tr><td> <i>C</i> in compression </td> <td> 4,668 </td> <td> 5,100 </td> <td> 6,466 </td> <td> 7,466 </td> <td> 8,985 </td> <td> 10,910 </td></tr> +<tr><td> Per cent <i>r</i> is in excess of <i>C</i> </td> <td> 5.5 </td> <td> 16.5 </td> <td> 7.1 </td> <td> 5.2 </td> <td> 3.3</td> <td> 5.9 </td></tr> +<tr><th colspan="7"> SPRUCE </th></tr> +<tr><th colspan="2"> MOISTURE CONDITION </th> <th> Soaked 30 per cent </th><th> Green 30 per cent </th><th> 10 per cent </th> <th> 8.1 per cent </th><th> Kiln-dry 3.9 per cent </th></tr> +<tr><td colspan="2"> Number of tests averaged </td> <td> 5 </td> <td> 4 </td> <td> 5 </td> <td> 3 </td> <td> 4 </td></tr> +<tr><td colspan="2"><i>r</i> in bending </td> <td> 3,002 </td> <td> 3,362 </td> <td> 6,458 </td> <td> 8,400 </td> <td> 10,170 </td></tr> +<tr><td colspan="2"><i>C</i> in compression </td> <td> 2,680 </td> <td> 3,025 </td> <td> 6,120 </td> <td> 7,610 </td> <td> 9,335 </td></tr> +<tr><td colspan="2"> Per cent <i>r</i> is in excess of <i>C</i> </td> <td> 12.0 </td> <td> 11.1</td> <td> 5.5 </td> <td> 10.4 </td> <td> 9.0 </td></tr> +</tbody> +</table> +</center> + +<p>When a short column is compressed until it breaks, the manner of +failure depends partly upon the anatomical structure and partly +upon the degree of humidity of the wood. The fibres (tracheids +in conifers) act as hollow tubes bound closely together, and in +giving way they either (1) buckle, or (2) bend.<a name="fn05r"></a><a href="#fn05"><sup><small>5</small></sup></a></p> + +<p>The first is typical of any dry thin-walled cells, as is usually +the case in seasoned white pine and spruce, and in the early +wood of hard pines, hemlock, and other species with decided +contrast between the two portions of the growth ring. As a rule +buckling of a tracheid begins at the bordered pits which form +places of least resistance in the walls. In hardwoods such as +oak, chestnut, ash, etc., buckling occurs only in the +thinnest-walled elements, such as the vessels, and not in the +true fibres.</p> + +<p>According to Jaccard<a name="fn06r"></a><a href="#fn06"><sup><small>6</small></sup></a> the folding of the cells is accompanied +by characteristic alterations of their walls which seem to split +them into extremely thin layers. When greatly magnified, these +layers appear in longitudinal sections as delicate threads +without <a name="pg017"></a> any definite arrangements, while on cross section they +appear as numerous concentric strata. This may be explained on +the ground that the growth of a fibre is by successive layers +which, under the influence of compression, are sheared apart. +This is particularly the case with thick-walled cells such as +are found in late wood.</p> + +<a name="pg016"></a> + +<center> +<table id="TABLE_06" summary="TABLE_VI" border="3" cellspacing="0" cellpadding="1" width="40%"> +<tbody> +<tr><th colspan="4"> TABLE VI </th></tr> +<tr><th colspan="4"> RESULTS OF ENDWISE COMPRESSION TESTS ON SMALL CLEAR PIECES OF 40 WOODS IN GREEN CONDITION </th></tr> +<tr><td colspan="4"> (Forest Service Cir. 213) </td></tr> +<tr><th rowspan="2"> COMMON NAME OF SPECIES </th> <th> Fibre stress at elastic limit </th> + <th> Crushing strength</th> + <th> Modulus of elasticity </th></tr> +<tr> <th><i>Lbs. per sq. inch</i></th> + <th><i>Lbs. per sq. inch</i></th> + <th><i>Lbs. per sq. inch</i></th></tr> +<tr><th> <i>Hardwoods</i> </th> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Ash, white </td> <td> 3,510 </td><td> 4,220 </td><td> 1,531,000 </td></tr> +<tr><td style="text-align: left;"> Basswood </td> <td> 780 </td> <td> 1,820 </td><td> 1,016,000 </td></tr> +<tr><td style="text-align: left;"> Beech </td> <td> 2,770 </td><td> 3,480 </td><td> 1,412,000 </td></tr> +<tr><td style="text-align: left;"> Birch, yellow </td> <td> 2,570 </td><td> 3,400 </td><td> 1,915,000 </td></tr> +<tr><td style="text-align: left;"> Elm, slippery </td> <td> 3,410 </td><td> 3,990 </td><td> 1,453,000 </td></tr> +<tr><td style="text-align: left;"> Hackberry </td> <td> 2,730 </td><td> 3,310 </td><td> 1,068,000 </td></tr> +<tr><td style="text-align: left;"> Hickory, big shellbark </td> <td> 3,570 </td><td> 4,520 </td><td> 1,658,000 </td></tr> +<tr><td style="text-align: left;"> bitternut </td> <td> 4,330 </td><td> 4,570 </td><td> 1,616,000 </td></tr> +<tr><td style="text-align: left;"> mockernut </td> <td> 3,990 </td><td> 4,320 </td><td> 1,359,000 </td></tr> +<tr><td style="text-align: left;"> nutmeg </td> <td> 3,620 </td><td> 3,980 </td><td> 1,411,000 </td></tr> +<tr><td style="text-align: left;"> pignut </td> <td> 3,520 </td><td> 4,820 </td><td> 1,980,000 </td></tr> +<tr><td style="text-align: left;"> shagbark </td> <td> 3,730 </td><td> 4,600 </td><td> 1,943,000 </td></tr> +<tr><td style="text-align: left;"> water </td> <td> 3,240 </td><td> 4,660 </td><td> 1,926,000 </td></tr> +<tr><td style="text-align: left;"> Locust, honey </td> <td> 4,300 </td><td> 4,970 </td><td> 1,536,000 </td></tr> +<tr><td style="text-align: left;"> Maple, sugar </td> <td> 3,040 </td><td> 3,670 </td><td> 1,463,000 </td></tr> +<tr><td style="text-align: left;"> Oak, post </td> <td> 2,780 </td><td> 3,330 </td><td> 1,062,000 </td></tr> +<tr><td style="text-align: left;"> red </td> <td> 2,290 </td><td> 3,210 </td><td> 1,295,000 </td></tr> +<tr><td style="text-align: left;"> swamp white </td> <td> 3,470 </td><td> 4,360 </td><td> 1,489,000 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 2,400 </td><td> 3,520 </td><td> 946,000 </td></tr> +<tr><td style="text-align: left;"> yellow </td> <td> 2,870 </td><td> 3,700 </td><td> 1,465,000 </td></tr> +<tr><td style="text-align: left;"> Osage orange </td> <td> 3,980 </td><td> 5,810 </td><td> 1,331,000 </td></tr> +<tr><td style="text-align: left;"> Sycamore </td> <td> 2,320 </td><td> 2,790 </td><td> 1,073,000 </td></tr> +<tr><td style="text-align: left;"> Tupelo </td> <td> 2,280 </td><td> 3,550 </td><td> 1,280,000 </td></tr> +<tr><th> <i>Conifers</i> </th> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Arborvitæ </td> <td> 1,420 </td><td> 1,990 </td><td> 754,000 </td></tr> +<tr><td style="text-align: left;"> Cedar, incense </td> <td> 2,710 </td><td> 3,030 </td><td> 868,000 </td></tr> +<tr><td style="text-align: left;"> Cypress, bald </td> <td> 3,560 </td><td> 3,960 </td><td> 1,738,000 </td></tr> +<tr><td style="text-align: left;"> Fir, alpine </td> <td> 1,660 </td><td> 2,060 </td><td> 882,000 </td></tr> +<tr><td style="text-align: left;"> amabilis </td> <td> 2,763 </td><td> 3,040 </td><td> 1,579,000 </td></tr> +<tr><td style="text-align: left;"> Douglas </td> <td> 2,390 </td><td> 2,920 </td><td> 1,440,000 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 2,610 </td><td> 2,800 </td><td> 1,332,000 </td></tr> +<tr><td style="text-align: left;"> Hemlock</td> <td> 2,110 </td><td> 2,750 </td><td> 1,054,000 </td></tr> +<tr><td style="text-align: left;"> Pine, lodgepole</td> <td> 2,290 </td><td> 2,530 </td><td> 1,219,000 </td></tr> +<tr><td style="text-align: left;"> longleaf </td> <td> 3,420 </td><td> 4,280 </td><td> 1,890,000 </td></tr> +<tr><td style="text-align: left;"> red </td> <td> 2,470 </td><td> 3,080 </td><td> 1,646,000 </td></tr> +<tr><td style="text-align: left;"> sugar </td> <td> 2,340 </td><td> 2,600 </td><td> 1,029,000 </td></tr> +<tr><td style="text-align: left;"> western yellow </td><td> 2,100 </td><td> 2,420 </td><td> 1,271,000 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 2,370 </td><td> 2,720 </td><td> 1,318,000 </td></tr> +<tr><td style="text-align: left;"> Redwood </td> <td> 3,420 </td><td> 3,820 </td><td> 1,175,000 </td></tr> +<tr><td style="text-align: left;"> Spruce, Engelmann </td> <td> 1,880 </td><td> 2,170 </td><td> 1,021,000 </td></tr> +<tr><td style="text-align: left;"> Tamarack </td> <td> 3,010 </td><td> 3,480 </td><td> 1,596,000 </td></tr> +</tbody> +</table> +</center> + +<p>The second case, where the fibres bend with more or less regular +curves instead of buckling, is characteristic of any green or +wet wood, and in dry woods where the fibres are thick-walled. In +woods in which the fibre walls show all gradations of +thickness—in other words, where the transition from the +thin-walled cells of the early wood to the thick-walled cells of +the late wood is gradual—the two kinds of failure, namely, +buckling and bending, grade into each other. In woods with very +decided contrast between early and late wood the two forms are +usually distinct. Except in the case of complete failure the +cavity of the deformed cells remains open, and in hardwoods this +is true not only of the wood fibres but also of the tube-like +vessels. In many cases longitudinal splits occur which isolate +bundles of elements by greater or less intervals. The splitting +occurs by a tearing of the fibres or rays and not by the +separation of the rays from the adjacent elements.</p> + +<p class="ctr"><img src="images/fig08.jpg" alt="Figure 8" id="fig08" /></p> +<p class="imgtitle">Figure 8</p> +<p class="imgtext"> Failures of short columns of green spruce.</p> + +<p class="ctr"><img src="images/fig09.jpg" alt="Figure 9" id="fig09" /></p> +<p class="imgtitle">Figure 9</p> +<p class="imgtext"> Failures of short columns of dry chestnut.</p> + +<p>Moisture in wood decreases the stiffness of the fibre walls and +enlarges the region of failure. The curve which the fibre walls +<a name="pg018"></a> +make in the region of failure is more gradual and also more +irregular than in dry wood, and the fibres are more likely to be +separated.</p> + +<p>In examining the lines of rupture in compression parallel to the +grain it appears that there does not exist any specific type, +that is, one that is characteristic of all woods. Test blocks +taken from different parts of the same log may show very decided +differences in the manner of failure, while blocks that are much +alike in the size, number, and distribution of the elements of +unequal resistance may behave very similarly. The direction of +rupture is, according to Jaccard, not influenced by the +distribution of the medullary rays.<a name="fn07r"></a><a href="#fn07"><sup><small>7</small></sup></a> These are curved with the +bundles of fibres to which they are attached. In any case the +failure starts at <a name="pg019"></a> the weakest points and follows the lines of +least resistance. The plane of failure, as visible on radial +surfaces, is horizontal, and on the tangential surface it is +diagonal.</p> + +<a name="I_05"></a> +<h3>SHEARING STRENGTH</h3> + +<p>Whenever forces act upon a body in such a way that one portion +tends to slide upon another adjacent to it the action is called +a <b>shear</b>.<a name="fn08r"></a><a href="#fn08"><sup><small>8</small></sup></a> In wood this shearing action may be (1) <b>along the +grain</b>, or (2) <b>across the grain</b>. A tenon breaking out its +mortise is a familiar example of shear along the grain, while +the shoving off of the tenon itself would be shear across the +grain. The use of wood for pins or tree-nails involves +resistance to shear across the grain. Another common instance of +the latter is where the steel edge of the eye of an axe or +hammer tends to cut off the handle. In <a href="#fig10">Fig. 10</a> the action of the +wooden strut tends to shear off along the grain the portion <i>AB</i> +of the wooden tie rod, and it is essential that the length of +this portion be great enough to guard against it. <a href="#fig11">Fig. 11</a> shows +characteristic failures in shear along the grain.</p> + +<p class="ctr"><img src="images/fig10.jpg" alt="Figure 10" id="fig10" /></p> +<p class="imgtitle">Figure 10</p> +<p class="imgtext"> Example of shear along the grain.</p> + +<p class="ctr"><img src="images/fig11.jpg" alt="Figure 11" id="fig11" /></p> +<p class="imgtitle">Figure 11</p> +<p class="imgtext"> Failures of test specimens in shear +along the grain. In the block at the left the surface of failure +is radial; in the one at the right, tangential.</p> + +<a name="pg020"></a> + +<center> +<table id="TABLE_07" summary="TABLE_VII" border="3" cellspacing="0" cellpadding="1" width="40%"> +<tbody> +<tr><th colspan="3"> TABLE VII </th></tr> +<tr><th colspan="3"> SHEARING STRENGTH ALONG THE GRAIN OF SMALL CLEAR PIECES OF 41 WOODS IN GREEN CONDITION </th></tr> +<tr><td colspan="3"> (Forest Service Cir. 213) </td></tr> +<tr><th rowspan="2"> COMMON NAME OF SPECIES </th> <th> When surface of failure is radial </th> + <th> When surface of failure is tangential </th></tr> +<tr> <th><i>Lbs. per sq. inch</i></th> + <th><i>Lbs. per sq. inch</i></th></tr> +<tr><th> <i>Hardwoods </i></th> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Ash, black </td> <td> 876 </td> <td> 832 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 1,360 </td><td> 1,312 </td></tr> +<tr><td style="text-align: left;"> Basswood </td> <td> 560 </td> <td> 617 </td></tr> +<tr><td style="text-align: left;"> Beech </td> <td> 1,154 </td><td> 1,375 </td></tr> +<tr><td style="text-align: left;"> Birch, yellow </td> <td> 1,103 </td><td> 1,188 </td></tr> +<tr><td style="text-align: left;"> Elm, slippery </td> <td> 1,197 </td><td> 1,174 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 778 </td> <td> 872 </td></tr> +<tr><td style="text-align: left;"> Hackberry </td> <td> 1,095 </td><td> 1,161 </td></tr> +<tr><td style="text-align: left;"> Hickory, big shellbark </td> <td> 1,134 </td><td> 1,191 </td></tr> +<tr><td style="text-align: left;"> bitternut </td> <td> 1,134 </td><td> 1,348 </td></tr> +<tr><td style="text-align: left;"> mockernut </td> <td> 1,251 </td><td> 1,313 </td></tr> +<tr><td style="text-align: left;"> nutmeg </td> <td> 1,010 </td><td> 1,053 </td></tr> +<tr><td style="text-align: left;"> pignut </td> <td> 1,334 </td><td> 1,457 </td></tr> +<tr><td style="text-align: left;"> shagbark </td> <td> 1,230 </td><td> 1,297 </td></tr> +<tr><td style="text-align: left;"> water </td> <td> 1,390 </td><td> 1,490 </td></tr> +<tr><td style="text-align: left;"> Locust, honey </td> <td> 1,885 </td><td> 2,096 </td></tr> +<tr><td style="text-align: left;"> Maple, red </td> <td> 1,130 </td><td> 1,330 </td></tr> +<tr><td style="text-align: left;"> sugar </td> <td> 1,193 </td><td> 1,455 </td></tr> +<tr><td style="text-align: left;"> Oak, post </td> <td> 1,196 </td><td> 1,402 </td></tr> +<tr><td style="text-align: left;"> red </td> <td> 1,132 </td><td> 1,195 </td></tr> +<tr><td style="text-align: left;"> swamp white </td> <td> 1,198 </td><td> 1,394 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 1,096 </td><td> 1,292 </td></tr> +<tr><td style="text-align: left;"> yellow </td> <td> 1,162 </td><td> 1,196 </td></tr> +<tr><td style="text-align: left;"> Sycamore </td> <td> 900 </td> <td> 1,102 </td></tr> +<tr><td style="text-align: left;"> Tupelo </td> <td> 978 </td> <td> 1,084 </td></tr> +<tr><th> <i>Conifers</i> </th> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Arborvitæ </td> <td> 617 </td> <td> 614 </td></tr> +<tr><td style="text-align: left;"> Cedar, incense </td> <td> 613 </td> <td> 662 </td></tr> +<tr><td style="text-align: left;"> Cypress, bald </td> <td> 836 </td> <td> 800 </td></tr> +<tr><td style="text-align: left;"> Fir, alpine </td> <td> 573 </td> <td> 654 </td></tr> +<tr><td style="text-align: left;"> amabilis </td> <td> 517 </td> <td> 639 </td></tr> +<tr><td style="text-align: left;"> Douglas </td> <td> 853 </td> <td> 858 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 742 </td> <td> 723 </td></tr> +<tr><td style="text-align: left;"> Hemlock </td> <td> 790 </td> <td> 813 </td></tr> +<tr><td style="text-align: left;"> Pine, lodgepole </td> <td> 672 </td> <td> 747 </td></tr> +<tr><td style="text-align: left;"> longleaf </td> <td> 1,060 </td><td> 953 </td></tr> +<tr><td style="text-align: left;"> red </td> <td> 812 </td> <td> 741 </td></tr> +<tr><td style="text-align: left;"> sugar </td> <td> 702 </td> <td> 714 </td></tr> +<tr><td style="text-align: left;"> western yellow </td><td> 686 </td> <td> 706 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 649 </td> <td> 639 </td></tr> +<tr><td style="text-align: left;"> Spruce, Engelmann </td> <td> 607 </td> <td> 624 </td></tr> +<tr><td style="text-align: left;"> Tamarack </td> <td> 883 </td> <td> 843 </td></tr> +</tbody> +</table> +</center> + +<a name="pg021"></a> + +<p>Both shearing stresses may act at the same time. Thus the weight +carried by a beam tends to shear it off at right angles to the +axis; this stress is equal to the resultant force acting +perpendicularly at any point, and in a beam uniformly loaded and +supported at either end is maximum at the points of support and +zero at the centre. In addition there is a shearing force +tending to move the fibres of the beam past each other in a +longitudinal direction. (<a href="#fig12">See Fig. 12</a>.) This longitudinal shear +is maximum at the neutral plane and decreases toward the upper +and lower surfaces.</p> + +<p class="ctr"><img src="images/fig12.jpg" alt="Figure 12" id="fig12" /></p> +<p class="imgtitle">Figure 12</p> +<p class="imgtext"> Horizontal shear in a beam.</p> + +<p>Shearing across the grain is so closely related to compression +at right angles to the grain and to hardness that there is +little to be gained by making separate tests upon it. Knowledge +of shear parallel to the grain is important, since wood +frequently fails in that way. The value of shearing stress +parallel to the grain is found by dividing the maximum load in +pounds (<i>P</i>) by the area of the cross section in inches (<i>A</i>).</p> + +<center> +<table summary="text"> +<tbody> +<tr><td rowspan="3"><big><big><big><big>(</big></big></big></big></td><td><br></td> <td><br></td><td><i>P</i></td><td rowspan="3"><big><big><big><big>)</big></big></big></big></td></tr> +<tr> <td>Shear</td><td>=</td> <td>---</td></tr> +<tr> <td><br></td> <td><br></td><td><i>A</i></td></tr> +</tbody> +</table> +</center> + +<p>Oblique shearing stresses are developed in a bar when it is + +subjected to direct tension or compression. The maximum <a name="pg022"></a> shearing +stress occurs along a plane when it makes an angle of 45 degrees +with the axis of the specimen. In this case,</p> + +<center> +<table summary="text"> +<tbody> +<tr><td><br></td> <td><br></td> <td><i>P</i></td></tr> +<tr><td>shear</td><td>=</td> <td>-----.</td></tr> +<tr><td><br></td> <td><br></td> <td>2 <i>A</i></td></tr> +</tbody> +</table> +</center> + +<p>When the value of the angle <i>θ</i> is less than 45 degrees,</p> + +<center> +<table summary="text"> +<tbody> +<tr><td><br></td> <td><br></td> <td><i>P</i></td><td><br></td></tr> +<tr><td>the shear along the plane</td><td>=</td> <td>---</td> <td>sin <i>θ</i> cos <i>θ</i>.</td></tr> +<tr><td><br></td> <td><br></td> <td><i>A</i></td><td><br></td></tr> +</tbody> +</table> +</center> + +<p>(<a href="#fig13">See Fig. 13</a>.) The effect of oblique shear is often +visible in the failures of short columns. (<a href="#fig14">See Fig. 14</a>.)</p> + +<p class="ctr"><img src="images/fig13.jpg" alt="Figure 13" id="fig13" /></p> +<p class="imgtitle">Figure 13</p> +<p class="imgtext"> Oblique shear in a short column.</p> + +<p class="ctr"><img src="images/fig14.jpg" alt="Figure 14" id="fig14" /></p> +<p class="imgtitle">Figure 14</p> +<p class="imgtext"> Failure of short column by oblique shear.</p> + +<center> +<table id="TABLE_08" summary="TABLE_VIII" border="3" cellspacing="0" cellpadding="1" width="60%"> +<tbody> +<tr><th colspan="4"> TABLE VIII </th></tr> +<tr><th colspan="4"> SHEARING STRENGTH ACROSS THE GRAIN OF VARIOUS AMERICAN WOODS </th></tr> +<tr><td colspan="4">(J.C. Trautwine. Jour. Franklin Institute. Vol. 109, 1880, pp. 105-106)</td></tr> +<tr><th> KIND OF WOOD </th> <th><i>Lbs. per sq. inch</i></th> + <th> KIND OF WOOD </th> <th><i>Lbs. per sq. inch</i></th></tr> +<tr><td style="text-align: left;"> Ash </td> <td> 6,280 </td><td style="text-align: left;"> Hickory </td> <td> 7,285 </td></tr> +<tr><td style="text-align: left;"> Beech </td> <td> 5,223 </td><td style="text-align: left;"> Locust </td> <td> 7,176 </td></tr> +<tr><td style="text-align: left;"> Birch </td> <td> 5,595 </td><td style="text-align: left;"> Maple </td> <td> 6,355 </td></tr> +<tr><td style="text-align: left;"> Cedar (white) </td> <td> 1,372 </td><td style="text-align: left;"> Oak </td> <td> 4,425 </td></tr> +<tr><td style="text-align: left;"> Cedar (white) </td> <td> 1,519 </td><td style="text-align: left;"> Oak (live) </td> <td> 8,480 </td></tr> +<tr><td style="text-align: left;"> Cedar (Central Amer.) </td><td> 3,410 </td><td style="text-align: left;"> Pine (white )</td> <td> 2,480 </td></tr> +<tr><td style="text-align: left;"> Cherry </td> <td> 2,945 </td><td style="text-align: left;"> Pine (northern yellow) </td> <td> 4,340 </td></tr> +<tr><td style="text-align: left;"> Chestnut </td> <td> 1,536 </td><td style="text-align: left;"> Pine (southernyellow) </td> <td> 5,735 </td></tr> +<tr><td style="text-align: left;"> Dogwood </td> <td> 6,510 </td><td style="text-align: left;"> Pine (very resinous yellow) </td><td> 5,053 </td></tr> +<tr><td style="text-align: left;"> Ebony </td> <td> 7,750 </td><td style="text-align: left;"> Poplar </td> <td> 4,418 </td></tr> +<tr><td style="text-align: left;"> Gum </td> <td> 5,890 </td><td style="text-align: left;"> Spruce </td> <td> 3,255 </td></tr> +<tr><td style="text-align: left;"> Hemlock </td> <td> 2,750 </td><td style="text-align: left;"> Walnut (black)</td> <td> 4,728 </td></tr> +<tr><td style="text-align: left;"> Hickory </td> <td> 6,045 </td><td style="text-align: left;"> Walnut (common)</td> <td> 2,830 </td></tr> +<tr><td style="text-align: left;" colspan="4"> NOTE.—Two specimens of each were tested. All were fairly seasoned and without defects. The piece sheared off was 5/8 in. The single circular area of each pin was 0.322 sq. in. </td></tr> +</tbody> +</table> +</center> + +<a name="I_06"></a> +<h3>TRANSVERSE OR BENDING STRENGTH: BEAMS</h3> + +<p>When external forces acting in the same plane are applied at +right angles to the axis of a bar so as to cause it to bend, +they occasion a shortening of the longitudinal fibres on the +concave side and an elongation of those on the convex side. +Within the elastic limit the relative stretching and contraction +of the fibres is directly<a name="fn09r"></a><a href="#fn09"><sup><small>9</small></sup></a>] proportional to their distances +from a plane <a name="pg023"></a> intermediate between them—the <b>neutral plane</b>. +(<i>N</i><sub><small>1</small></sub><i>P</i> in <a href="#fig15">Fig. 15</a>.) Thus the fibres half-way between the +neutral plane and the outer surface experience only half as much +shortening or elongation as the outermost or extreme fibres. +Similarly for other distances. The elements along the neutral +plane experience no tension or compression in an axial +direction. The line of intersection of this plane and the plane +of section is known as the <b>neutral axis</b> (<i>N A</i> in <a href="#fig15">Fig. 15</a>.) of +the section.</p> + +<p class="ctr"><img src="images/fig15.jpg" alt="Figure 15" id="fig15" /></p> +<p class="imgtitle">Figure 15</p> +<p class="imgtext"> Diagram of a simple beam. <i>N</i><sub><small>1</small></sub><i>P</i> = +neutral plane, <i>N A</i> = neutral axis of section <i>R S</i>.</p> + +<p>If the bar is symmetrical and homogeneous the neutral plane is +located half-way between the upper and lower surfaces, so long +as the deflection does not exceed the elastic limit of the +material. Owing to the fact that the tensile strength of wood is +from two to nearly four times the compressive strength, it +follows that at rupture the neutral plane is much nearer the +convex than the concave side of the bar or beam, since the sum +of all the compressive stresses on the concave portion must +always equal the sum of the tensile stresses on the convex +portion. The neutral plane begins to change from its central +position as soon as the elastic limit has been passed. Its +location at any time is very uncertain.</p> + +<p>The external forces acting to bend the bar also tend to rupture +it at right angles to the neutral plane by causing one +transverse section to slip past another. This stress at any +point is equal to the resultant perpendicular to the axis of the +forces acting at this point, and is termed the <b>transverse +shear</b> (or in the case of beams, <b>vertical shear</b>).</p> + +<a name="pg024"></a> + +<p>In addition to this there is a shearing stress, tending to move +the fibres past one another in an axial direction, which is +called <b>longitudinal shear</b> (or in the case of beams, +<b>horizontal shear</b>). This stress must be taken into +consideration in the design of timber structures. It is maximum +at the neutral plane and decreases to zero at the outer elements +of the section. The shorter the span of a beam in proportion to +its height, the greater is the liability of failure in +horizontal shear before the ultimate strength of the beam is +reached.</p> + +<h4><i>Beams</i></h4> + +<p>There are three common forms of beams, as follows:</p> + +<p>(1) <b>Simple beam</b>—a bar resting upon two supports, one near +each end. (<a href="#fig16">See Fig. 16</a>, No. 1.)</p> + +<p>(2) <b>Cantilever beam</b>—a bar resting upon one support or +fulcrum, or that portion of any beam projecting out of a wall or +beyond a support. (<a href="#fig16">See Fig. 16</a>, No. 2.)</p> + +<p>(3) <b>Continuous beam</b>—a bar resting upon more than two +supports. (<a href="#fig16">See Fig. 16</a>, No. 3.)</p> + +<p class="ctr"><img src="images/fig16.jpg" alt="Figure 16" id="fig16" /></p> +<p class="imgtitle">Figure 16</p> +<p class="imgtext"> Three common forms of beams. 1. Simple. 2. Cantilever. 3. Continuous.</p> + +<a name="pg025"></a> + +<h4><i>Stiffness of Beams</i></h4> + +<p>The two main requirements of a beam are stiffness and strength. +The formulæ for the <i>modulus of elasticity (E)</i> or measure of +stiffness of a rectangular prismatic simple beam loaded at the +centre and resting freely on supports at either end is:<a name="fn10r"></a><a href="#fn10"><sup><small>10</small></sup></a></p> + +<center> +<table summary="text"> +<tbody> +<tr><td><br></td> <td><br></td><td><i>P' l</i><sup><small>3</small></sup></td></tr> +<tr><td><i>E</i></td> <td>=</td> <td>-----------</td></tr> +<tr><td><br></td> <td><br></td><td><i>4 D b h</i><sup><small>3</small></sup></td></tr> +<tr><td><br></td> <td><br></td><td><br></td></tr> +<tr><td><i>b</i></td> <td>=</td> <td style="text-align: left;"> breadth or width of beam, inches. </td></tr> +<tr><td><i>h</i></td> <td>=</td> <td style="text-align: left;"> height or depth of beam, inches. </td></tr> +<tr><td><i>l</i></td> <td>=</td> <td style="text-align: left;"> span (length between points of supports) of beam, inches. </td></tr> +<tr><td><i>D</i></td> <td>=</td> <td style="text-align: left;"> deflection produced by load <i>P'</i>, inches. </td></tr> +<tr><td><i>P'</i></td><td>=</td> <td style="text-align: left;"> load at or below elastic limit, pounds. </td></tr> +</tbody> +</table> +</center> + +<p>From this formulæ it is evident that for rectangular beams of +the same material, mode of support, and loading, the deflection +is affected as follows:</p> + +<p>(1) It is inversely proportional to the width for beams of the +same length and depth. If the width is tripled the deflection is +one-third as great.</p> + +<p>(2) It is inversely proportional to the cube of the depth for +beams of the same length and breadth. If the depth is tripled +the deflection is one twenty-seventh as great.</p> + +<p>(3) It is directly proportional to the cube of the span for +beams of the same breadth and depth. Tripling the span gives +twenty-seven times the deflection.</p> + +<p>The number of pounds which concentrated at the centre will +deflect a rectangular prismatic simple beam one inch may be +found from the preceding formulæ by substituting <i>D</i> = 1" and +solving for <i>P'</i>. The formulæ then becomes:</p> + +<center> +<table summary="text"> +<tbody> +<tr><td><br></td> <td><br></td> <td>4 <i>E b h</i><sup><small>3</small></sup></td></tr> +<tr><td>Necessary weight (<i>P'</i>)</td><td>=</td> <td>----------</td></tr> +<tr><td><br></td> <td><br></td> <td><i>l</i><sup><small>3</small></sup></td></tr> +</tbody> +</table> +</center> + +<p>In this case the values for <i>E</i> are read from tables prepared from +data obtained by experimentation on the given material. + +<a name="pg026"></a> + +<h4><i>Strength of Beams</i></h4> + +<p>The measure of the breaking strength of a beam is expressed in +terms of unit stress by a <i>modulus of rupture</i>, which is a +purely hypothetical expression for points beyond the elastic +limit. The formulæ used in computing this modulus is as follows:</p> + +<center> +<table summary="text"> +<tbody> +<tr><td><br></td> <td><br></td> <td> 1.5 <i>P l</i></td></tr> +<tr><td> <i>R</i> </td> <td>=</td> <td>---------</td></tr> +<tr><td><br></td> <td><br></td> <td> <i>b h</i><sup><small>2</small></sup></td></tr> +<tr><td><br></td> <td><br></td><td><br></td></tr> +<tr><td><i>b, h, l</i></td> <td>=</td> <td style="text-align: left;"> breadth, height, and span, respectively, as in preceding formulæ. </td></tr> +<tr><td><i>R</i></td> <td>=</td> <td style="text-align: left;"> modulus of rupture, pounds per square inch. </td></tr> +<tr><td><i>P</i></td> <td>=</td> <td style="text-align: left;"> maximum load, pounds. </td></tr> +</tbody> +</table> +</center> + +<p>In calculating the fibre stress at the elastic limit the same +formulæ is used except that the load at elastic limit (<i>P</i><sub><small>1</small></sub>) is +substituted for the maximum load (<i>P</i>).</p> + +<p>From this formulæ it is evident that for rectangular prismatic +beams of the same material, mode of support, and loading, the +load which a given beam can support varies as follows:</p> + +<p>(1) It is directly proportional to the breadth for beams of the +same length and depth, as is the case with stiffness.</p> + +<p>(2) It is directly proportional to the square of the height for +beams of the same length and breadth, instead of as the cube of +this dimension as in stiffness.</p> + +<p>(3) It is inversely proportional to the span for beams of the +same breadth and depth and not to the cube of this dimension as +in stiffness.</p> + +<p>The fact that the strength varies as the <i>square</i> of the height +and the stiffness as the <i>cube</i> explains the relationship of +bending to thickness. Were the law the same for strength and +stiffness a thin piece of material such as a sheet of paper +could not be bent any further without breaking than a thick +piece, say an inch board.</p> + +<a name="pg027"></a> + +<center> +<table id="TABLE_09" summary="TABLE_IX" border="3" cellspacing="0" cellpadding="1" width="60%"> +<tbody> +<tr><th colspan="7"> TABLE IX </th></tr> +<tr><th colspan="7"> RESULTS OF STATIC BENDING TESTS ON SMALL CLEAR BEAMS OF 49 WOODS IN GREEN CONDITION </th></tr> +<tr><td colspan="7"> (Forest Service Cir. 213) </td></tr> +<tr><th rowspan="3"> COMMON NAME OF SPECIES </th> <th rowspan="2"> Fibre stress at elastic limit </th> + <th rowspan="2"> Modulus of rupture </th> + <th rowspan="2"> Modulus of elasticity </th> + <th colspan="3"> Work in Bending </th></tr> +<tr> <th> To elastic limit </th> + <th> To maximum load </th> + <th> Total </th></tr> +<tr> <th><i>Lbs. per sq. in.</i></th> + <th><i>Lbs. per sq. in.</i></th> + <th><i>Lbs. per sq. in.</i></th> + <th><i>In.-lbs. per cu. inch</i></th> + <th><i>In.-lbs. per cu. inch</i></th> + <th><i>In.-lbs. per cu. inch</i></th></tr> +<tr><th> <i>Hardwoods</i> </th> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Ash, black </td> <td> 2,580 </td><td> 6,000 </td> <td> 960,000 </td> <td> 0.41 </td><td> 13.1 </td><td> 38.9 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 5,180 </td><td> 9,920 </td> <td> 1,416,000 </td><td> 1.10 </td><td> 20.0 </td><td> 43.7 </td></tr> +<tr><td style="text-align: left;"> Basswood </td> <td> 2,480 </td><td> 4,450 </td> <td> 842,000 </td> <td> .45 </td> <td> 5.8 </td> <td> 8.9 </td></tr> +<tr><td style="text-align: left;"> Beech </td> <td> 4,490 </td><td> 8,610 </td> <td> 1,353,000 </td><td> .96 </td> <td> 14.1 </td><td> 31.4 </td></tr> +<tr><td style="text-align: left;"> Birch, yellow </td> <td> 4,190 </td><td> 8,390 </td> <td> 1,597,000 </td><td> .62 </td> <td> 14.2 </td><td> 31.5 </td></tr> +<tr><td style="text-align: left;"> Elm, rock </td> <td> 4,290 </td><td> 9,430 </td> <td> 1,222,000 </td><td> .90 </td> <td> 19.4 </td><td> 47.4 </td></tr> +<tr><td style="text-align: left;"> slippery </td> <td> 5,560 </td><td> 9,510 </td> <td> 1,314,000 </td><td> 1.32 </td><td> 11.7 </td><td> 44.2 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 2,850 </td><td> 6,940 </td> <td> 1,052,000 </td><td> .44 </td> <td> 11.8 </td><td> 27.4 </td></tr> +<tr><td style="text-align: left;"> Gum, red </td> <td> 3,460 </td><td> 6,450 </td> <td> 1,138,000 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Hackberry </td> <td> 3,320 </td><td> 7,800 </td> <td> 1,170,000 </td><td> .56 </td> <td> 19.6 </td><td> 52.9 </td></tr> +<tr><td style="text-align: left;"> Hickory, big shellbark </td> <td> 6,370 </td><td> 11,110 </td><td> 1,562,000 </td><td> 1.47 </td><td> 24.3 </td><td> 78.0 </td></tr> +<tr><td style="text-align: left;"> bitternut </td> <td> 5,470 </td><td> 10,280 </td><td> 1,399,000 </td><td> 1.22 </td><td> 20.0 </td><td> 75.5 </td></tr> +<tr><td style="text-align: left;"> mockernut </td> <td> 6,550 </td><td> 11,110 </td><td> 1,508,000 </td><td> 1.50 </td><td> 31.7 </td><td> 84.4 </td></tr> +<tr><td style="text-align: left;"> nutmeg </td> <td> 4,860 </td><td> 9,060 </td> <td> 1,289,000 </td><td> 1.06 </td><td> 22.8 </td><td> 58.2 </td></tr> +<tr><td style="text-align: left;"> pignut </td> <td> 5,860 </td><td> 11,810 </td><td> 1,769,000 </td><td> 1.12 </td><td> 30.6 </td><td> 86.7 </td></tr> +<tr><td style="text-align: left;"> shagbark </td> <td> 6,120 </td><td> 11,000 </td><td> 1,752,000 </td><td> 1.22 </td><td> 18.3 </td><td> 72.3 </td></tr> +<tr><td style="text-align: left;"> water </td> <td> 5,980 </td><td> 10,740 </td><td> 1,563,000 </td><td> 1.29 </td><td> 18.8 </td><td> 52.9 </td></tr> +<tr><td style="text-align: left;"> Locust, honey </td> <td> 6,020 </td><td> 12,360 </td><td> 1,732,000 </td><td> 1.28 </td><td> 17.3 </td><td> 64.4 </td></tr> +<tr><td style="text-align: left;"> Maple, red </td> <td> 4,450 </td><td> 8,310 </td> <td> 1,445,000 </td><td> .78 </td> <td> 9.8 </td> <td> 17.1 </td></tr> +<tr><td style="text-align: left;"> sugar </td> <td> 4,630 </td><td> 8,860 </td> <td> 1,462,000 </td><td> .88 </td> <td> 12.7 </td><td> 32.0 </td></tr> +<tr><td style="text-align: left;"> Oak, post </td> <td> 4,720 </td><td> 7,380 </td> <td> 913,000 </td> <td> 1.39 </td><td> 9.1 </td> <td> 17.4 </td></tr> +<tr><td style="text-align: left;"> red </td> <td> 3,490 </td><td> 7,780 </td> <td> 1,268,000 </td><td> .60 </td> <td> 11.4 </td><td> 26.0 </td></tr> +<tr><td style="text-align: left;"> swamp white </td> <td> 5,380 </td><td> 9,860 </td> <td> 1,593,000 </td><td> 1.05 </td><td> 14.5 </td><td> 37.6 </td></tr> +<tr><td style="text-align: left;"> tanbark </td> <td> 6,580 </td><td> 10,710 </td><td> 1,678,000 </td><td> 1.49 </td><td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> white </td> <td> 4,320 </td><td> 8,090 </td> <td> 1,137,000 </td><td> .95 </td> <td> 12.1 </td><td> 36.7 </td></tr> +<tr><td style="text-align: left;"> yellow </td> <td> 5,060 </td><td> 8,570 </td> <td> 1,219,000 </td><td> 1.20 </td><td> 11.7 </td><td> 30.7 </td></tr> +<tr><td style="text-align: left;"> Osage orange </td> <td> 7,760 </td><td> 13,660 </td><td> 1,329,000 </td><td> 2.53 </td><td> 37.9 </td><td> 101.7 </td></tr> +<tr><td style="text-align: left;"> Sycamore </td> <td> 2,820 </td><td> 6,300 </td> <td> 961,000 </td> <td> .51 </td> <td> 7.1 </td> <td> 13.6 </td></tr> +<tr><td style="text-align: left;"> Tupelo </td> <td> 4,300 </td><td> 7,380 </td> <td> 1,045,000 </td><td> 1.00 </td><td> 7.8 </td> <td> 20.9 </td></tr> +<tr><th> <i>Conifers</i></th> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Arborvitæ </td> <td> 2,600 </td><td> 4,250 </td> <td> 643,000 </td> <td> .60 </td> <td> 5.7 </td> <td> 9.5 </td></tr> +<tr><td style="text-align: left;"> Cedar, incense </td> <td> 3,950 </td><td> 6,040 </td> <td> 754,000 </td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Cypress, bald </td> <td> 4,430 </td><td> 7,110 </td> <td> 1,378,000 </td><td> .96 </td> <td> 5.1 </td> <td> 15.4 </td></tr> +<tr><td style="text-align: left;"> Fir, alpine </td> <td> 2,366 </td><td> 4,450 </td> <td> 861,000 </td> <td> .66 </td> <td> 4.4 </td> <td> 7.4 </td></tr> +<tr><td style="text-align: left;"> amabilis </td> <td> 4,060 </td><td> 6,570 </td> <td> 1,323,000 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Douglas </td> <td> 3,570 </td><td> 6,340 </td> <td> 1,242,000 </td><td> .59 </td> <td> 6.6 </td> <td> 13.6 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 3,880 </td><td> 5,970 </td> <td> 1,131,000 </td><td> .77 </td> <td> 5.2 </td> <td> 14.9 </td></tr> +<tr><td style="text-align: left;"> Hemlock </td> <td> 3,410 </td><td> 5,770 </td> <td> 917,000 </td> <td> .73 </td> <td> 6.6 </td> <td> 12.9 </td></tr> +<tr><td style="text-align: left;"> Pine, lodgepole </td> <td> 3,080 </td><td> 5,130 </td> <td> 1,015,000 </td><td> .54 </td> <td> 5.1 </td> <td> 7.4 </td></tr> +<tr><td style="text-align: left;"> longleaf </td> <td> 5,090 </td><td> 8,630 </td> <td> 1,662,000 </td><td> .88 </td> <td> 8.1 </td> <td> 34.8 </td></tr> +<tr><td style="text-align: left;"> red </td> <td> 3,740 </td><td> 6,430 </td> <td> 1,384,000 </td><td> .59 </td> <td> 5.8 </td> <td> 28.0 </td></tr> +<tr><td style="text-align: left;"> shortleaf </td> <td> 4,360 </td><td> 7,710 </td> <td> 1,395,000 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> sugar </td> <td> 3,330 </td><td> 5,270 </td> <td> 966,000 </td> <td> .66 </td> <td> 5.0 </td> <td> 11.6 </td></tr> +<tr><td style="text-align: left;"> west, yellow </td><td> 3,180 </td><td> 5,180 </td> <td> 1,111,000 </td><td> .52 </td> <td> 4.3 </td> <td> 15.6 </td></tr> +<tr><td style="text-align: left;"> White </td> <td> 3,410 </td><td> 5,310 </td> <td> 1,073,000 </td><td> .62 </td> <td> 5.9 </td> <td> 13.3 </td></tr> +<tr><td style="text-align: left;"> Redwood </td> <td> 4,530 </td><td> 6,560 </td> <td> 1,024,000 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Spruce, Engelmann </td> <td> 2,740 </td><td> 4,550 </td> <td> 866,000 </td> <td> .50 </td> <td> 4.8 </td> <td> 6.1 </td></tr> +<tr><td style="text-align: left;"> red </td> <td> 3,440 </td><td> 5,820 </td> <td> 1,143,000 </td><td> .62 </td> <td> 6.0 </td> <td><br></td></tr> +<tr><td style="text-align: left;"> white </td> <td> 3,160 </td><td> 5,200 </td> <td> 968,000 </td> <td> .58 </td> <td> 6.6 </td> <td><br></td></tr> +<tr><td style="text-align: left;"> Tamarack </td> <td> 4,200 </td><td> 7,170 </td> <td> 1,236,000 </td><td> .84 </td> <td> 7.2 </td> <td> 30.0 </td></tr> +</tbody> +</table> +</center> + +<h4><i>Kinds of Loads</i></h4> + +<p>There are various ways in which beams are loaded, of which the +following are the most important:</p> + +<p>(1) <b>Uniform load</b> occurs where the load is spread evenly over +the beam.</p> + +<a name="pg028"></a> + +<p>(2) <b>Concentrated load</b> occurs where the load is applied at +single point or points.</p> + +<p>(3) <b>Live</b> or <b>immediate load</b> is one of momentary or short +duration at any one point, such as occurs in crossing a bridge.</p> + +<p>(4) <b>Dead</b> or <b>permanent load</b> is one of constant and +indeterminate duration, as books on a shelf. In the case of a +bridge the weight of the structure itself is the dead load. All +large beams support a uniform dead load consisting of their own +weight.</p> + +<p>The effect of dead load on a wooden beam may be two or more +times that produced by an immediate load of the same weight. +Loads greater than the elastic limit are unsafe and will +generally result in rupture if continued long enough. A beam may +be considered safe under permanent load when the deflections +diminish during equal successive periods of time. A continual +increase in deflection indicates an unsafe load which is almost +certain to rupture the beam eventually.</p> + +<p>Variations in the humidity of the surrounding air influence the +deflection of dry wood under dead load, and increased +deflections during damp weather are cumulative and not recovered +by subsequent drying. In the case of longleaf pine, dry beams +may with safety be loaded permanently to within three-fourths of +their elastic limit as determined from ordinary static tests. +Increased moisture content, due to greater humidity of the air, +lowers the elastic limit of wood so that what was a safe load +for the dry material may become unsafe.</p> + +<p>When a dead load not great enough to rupture a beam has been +removed, the beam tends gradually to recover its former shape, +but the recovery is not always complete. If specimens from such +a beam are tested in the ordinary testing machine it will be +found that the application of the dead load did not affect the +stiffness, ultimate strength, or elastic limit of the material. +In other words, the deflections and recoveries produced by live +loads are the same as would have been produced had not the beam +previously been subjected to a dead load.<a name="fn11r"></a><a href="#fn11"><sup><small>11</small></sup></a></p> + +<a name="pg029"></a> + +<p><b>Maximum load</b> is the greatest load a material will support and +is usually greater than the load at rupture.</p> + +<p><b>Safe load</b> is the load considered safe for a material to +support in actual practice. It is always less than the load at +elastic limit and is usually taken as a certain proportion of +the ultimate or breaking load.</p> + +<p>The ratio of the breaking to the safe load is called the factor +of safety.</p> + +<center> +<table summary="text"> +<tbody> +<tr><td rowspan="3"><big><big><big><big>(</big></big></big></big></td><td><br></td> <td><br></td><td>ultimate strength</td><td rowspan="3"><big><big><big><big>)</big></big></big></big></td></tr> +<tr> <td>Factor of safety<br></td><td>=</td> <td>-------------------<br></td></tr> +<tr> <td><br></td> <td><br></td> <td>safe load<br></td></tr> +</tbody> +</table> +</center> + +<p>In +order to make due allowance for the natural variations and +imperfections in wood and in the aggregate structure, as well as +for variations in the load, the factor of safety is usually as +high as 6 or 10, especially if the safety of human life depends +upon the structure. This means that only from one-sixth to +one-tenth of the computed strength values is considered safe to +use. If the depth of timbers exceeds four times their thickness +there is a great tendency for the material to twist when loaded. +It is to overcome this tendency that floor joists are braced at +frequent intervals. Short deep pieces shear out or split before +their strength in bending can fully come into play. + +<h4><i>Application of Loads</i></h4> + +<p>There are three<a name="fn12r"></a><a href="#fn12"><sup><small>12</small></sup></a> general methods in which loads may be +applied to beams, namely:</p> + +<p>(1) <b>Static loading</b> or the gradual imposition of load so that +the moving parts acquire no appreciable momentum. Loads are so +applied in the ordinary testing machine.</p> + +<p>(2) <b>Sudden imposition of load without initial velocity.</b> "Thus +in the case of placing a load on a beam, if the load be brought +into contact with the beam, but its weight sustained by external +means, as by a cord, and then this external support be +<i>suddenly</i> (instantaneously) removed, as by quickly cutting the +cord, then, although the load is already touching the beam (and +hence there is no real impact), yet the beam is at first +offering no resistance, as it has yet suffered no deformation. +Furthermore, as the beam deflects the <a name="pg030"></a> resistance increases, but +does not come to be equal to the load until it has attained its +normal deflection. In the meantime there has been an unbalanced +force of gravity acting, of a constantly diminishing amount, +equal at first to the entire load, at the normal deflection. But +at this instant the load and the beam are in motion, the +hitherto unbalanced force having produced an accelerated +velocity, and this velocity of the weight and beam gives to them +an energy, or <i>vis viva</i>, which must now spend itself in +overcoming an <i>excess</i> of resistance over and above the imposed +load, and the whole mass will not stop until the deflection (as +well as the resistance) has come to be equal to <i>twice</i> that +corresponding to the static load imposed. Hence we say the +effect of a suddenly imposed load is to produce twice the +deflection and stress of the same load statically applied. It +must be evident, however, that this case has nothing in common +with either the ordinary 'static' tests of structural materials +in testing-machines, or with impact tests."<a name="fn13r"></a><a href="#fn13"><sup><small>13</small></sup></a></p> + +<p>(3) <b>Impact, shock,</b> or <b>blow.</b><a name="fn14r"></a><a href="#fn14"><sup><small>14</small></sup></a> There are various common +uses of wood where the material is subjected to sudden shocks +and jars or impact. Such is the action on the felloes and spokes +of a wagon wheel passing over a rough road; on a hammer handle +when a blow is struck; on a maul when it strikes a wedge.</p> + +<p>Resistance to impact is resistance to energy which is measured +by the product of the force into the space through which it +moves, or by the product of one-half the moving mass which +causes the shock into the square of its velocity. The work done +upon the piece at the instant the velocity is entirely removed +from the striking body is equal to the total energy of that +body. It is impossible, however, to get all of the energy of the +striking body stored in the specimen, though the greater the +mass and the shorter the space through which it moves, or, in +other words, the greater the proportion of weight and the +smaller the proportion of velocity making up the energy of the +striking body, the more energy the specimen will absorb. The +rest is lost in friction, vibrations, heat, and motion of the +anvil.</p> + +<a name="pg031"></a> + +<p>In impact the stresses produced become very complex and +difficult to measure, especially if the velocity is high, or the +mass of the beam itself is large compared to that of the weight.</p> + +<p>The difficulties attending the measurement of the stresses +beyond the elastic limit are so great that commonly they are not +reckoned. Within the elastic limit the formulæ for calculating +the stresses are based on the assumption that the deflection is +proportional to the stress in this case as in static tests.</p> + +<p>A common method of making tests upon the resistance of wood to +shock is to support a small beam at the ends and drop a heavy +weight upon it in the middle. (<a href="#fig40">See Fig. 40</a>.) The height of the +weight is increased after each drop and records of the +deflection taken until failure. The total work done upon the +specimen is equal to the area of the stress-strain diagram plus +the effect of local inertia of the molecules at point of +contact.</p> + +<p>The stresses involved in impact are complicated by the fact that +there are various ways in which the energy of the striking body +may be spent:</p> + +<p>(<i>a</i>) It produces a local deformation of both bodies at the +surface of contact, within or beyond the elastic limit. In +testing wood the compression of the substance of the steel +striking-weight may be neglected, since the steel is very hard +in comparison with the wood. In addition to the compression of +the fibres at the surface of contact resistance is also offered +by the inertia of the particles there, the combined effect of +which is a stress at the surface of contact often entirely out +of proportion to the compression which would result from the +action of a static force of the same magnitude. It frequently +exceeds the crushing strength at the extreme surface of contact, +as in the case of the swaging action of a hammer on the head of +an iron spike, or of a locomotive wheel on the steel rail. This +is also the case when a bullet is shot through a board or a pane +of glass without breaking it as a whole.</p> + +<p>(<i>b</i>) It may move the struck body as a whole with an accelerated +velocity, the resistance consisting of the inertia of the body. +This effect is seen when a croquet ball is struck with a mallet.</p> + +<p>(<i>c</i>) It may deform a fixed body against its external supports +and resistances. In making impact tests in the laboratory the +test specimen is in reality in the nature of a cushion between +two <a name="pg032"></a> impacting bodies, namely, the striking weight and the base +of the machine. It is important that the mass of this base be +sufficiently great that its relative velocity to that of the +common centre of gravity of itself and the striking weight may +be disregarded.</p> + +<p>(<i>d</i>) It may deform the struck body as a whole against the +resisting stresses developed by its own inertia, as, for +example, when a baseball bat is broken by striking the ball.</p> + +<center> +<table id="TABLE_10" summary="TABLE_X" border="3" cellspacing="0" cellpadding="1" width="40%"> +<tbody> +<tr><th colspan="4"> TABLE X </th></tr> +<tr><th colspan="4"> RESULTS OF IMPACT BENDING TESTS ON SMALL CLEAR BEAMS OF 34 WOODS IN GREEN CONDITION </th></tr> +<tr><td colspan="4"> (Forest Service Cir. 213) </td></tr> +<tr><th rowspan="2"> COMMON NAME OF SPECIES </th> <th> Fibre stress at elastic limit </th> + <th> Modulus of elasticity </th> + <th> Work in bending to elastic limit </th></tr> +<tr> <th> <i>Lbs. per sq. in.</i></th> + <th><i>Lbs. per sq. in.</i></th> + <th><i>In.-lbs. per cu. inch</i></th></tr> +<tr><th> <i>Hardwoods</i> </th> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Ash, black</td> <td> 7,840 </td> <td> 955,000 </td> <td> 3.69 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 11,710 </td><td> 1,564,000 </td><td> 4.93 </td></tr> +<tr><td style="text-align: left;"> Basswood </td> <td> 5,480 </td> <td> 917,000 </td> <td> 1.84 </td></tr> +<tr><td style="text-align: left;"> Beech </td> <td> 11,760 </td><td> 1,501,000 </td><td> 5.10 </td></tr> +<tr><td style="text-align: left;"> Birch, yellow </td> <td> 11,080 </td><td> 1,812,000 </td><td> 3.79 </td></tr> +<tr><td style="text-align: left;"> Elm, rock </td> <td> 12,090 </td><td> 1,367,000 </td><td> 6.52 </td></tr> +<tr><td style="text-align: left;"> slippery </td> <td> 11,700 </td><td> 1,569,000 </td><td> 4.86 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 9,910 </td> <td> 1,138,000 </td><td> 4.82 </td></tr> +<tr><td style="text-align: left;"> Hackberry </td> <td> 10,420 </td><td> 1,398,000 </td><td> 4.48 </td></tr> +<tr><td style="text-align: left;"> Locust, honey </td> <td> 13,460 </td><td> 2,114,000 </td><td> 4.76 </td></tr> +<tr><td style="text-align: left;"> Maple, red </td> <td> 11,670 </td><td> 1,411,000 </td><td> 5.45 </td></tr> +<tr><td style="text-align: left;"> sugar </td> <td> 11,680 </td><td> 1,680,000 </td><td> 4.55 </td></tr> +<tr><td style="text-align: left;"> Oak, post </td> <td> 11,260 </td><td> 1,596,000 </td><td> 4.41 </td></tr> +<tr><td style="text-align: left;"> red </td> <td> 10,580 </td><td> 1,506,000 </td><td> 4.16 </td></tr> +<tr><td style="text-align: left;"> swamp white </td> <td> 13,280 </td><td> 2,048,000 </td><td> 4.79 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 9,860 </td> <td> 1,414,000 </td><td> 3.84 </td></tr> +<tr><td style="text-align: left;"> yellow </td> <td> 10,840 </td><td> 1,479,000 </td><td> 4.44 </td></tr> +<tr><td style="text-align: left;"> Osage orange </td> <td> 15,520 </td><td> 1,498,000 </td><td> 8.92 </td></tr> +<tr><td style="text-align: left;"> Sycamore </td> <td> 8,180 </td> <td> 1,165,000 </td><td> 3.22 </td></tr> +<tr><td style="text-align: left;"> Tupelo </td> <td> 7,650 </td> <td> 1,310,000 </td><td> 2.49 </td></tr> +<tr><th> <i>Conifers</i> </th> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Arborvitæ </td> <td> 5,290 </td> <td> 778,000 </td> <td> 2.04 </td></tr> +<tr><td style="text-align: left;"> Cypress, bald </td> <td> 8,290 </td> <td> 1,431,000 </td><td> 2.71 </td></tr> +<tr><td style="text-align: left;"> Fir, alpine </td> <td> 5,280 </td> <td> 980,000 </td> <td> 1.59 </td></tr> +<tr><td style="text-align: left;"> Douglas </td> <td> 8,870 </td> <td> 1,579,000 </td><td> 2.79 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 7,230 </td> <td> 1,326,000 </td><td> 2.21 </td></tr> +<tr><td style="text-align: left;"> Hemlock </td> <td> 6,330 </td> <td> 1,025,000 </td><td> 2.19 </td></tr> +<tr><td style="text-align: left;"> Pine, lodgepole </td> <td> 6,870 </td> <td> 1,142,000 </td><td> 2.31 </td></tr> +<tr><td style="text-align: left;"> longleaf </td> <td> 9,680 </td> <td> 1,739,000 </td><td> 3.02 </td></tr> +<tr><td style="text-align: left;"> red </td> <td> 7,480 </td> <td> 1,438,000 </td><td> 2.18 </td></tr> +<tr><td style="text-align: left;"> sugar </td> <td> 6,740 </td> <td> 1,083,000 </td><td> 2.34 </td></tr> +<tr><td style="text-align: left;"> western yellow </td><td> 7,070 </td> <td> 1,115,000 </td><td> 2.51 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 6,490 </td> <td> 1,156,000 </td><td> 2.06 </td></tr> +<tr><td style="text-align: left;"> Spruce, Engelmann </td> <td> 6,300 </td> <td> 1,076,000 </td><td> 2.09 </td></tr> +<tr><td style="text-align: left;"> Tamarack </td> <td> 7,750 </td> <td> 1,263,000 </td><td> 2.67 </td></tr> +</tbody> +</table> +</center> + +<a name="pg033"></a> + +<p>Impact testing is difficult to conduct satisfactorily and the +data obtained are of chief value in a relative sense, that is, +for comparing the shock-resisting ability of woods of which like +specimens have been subjected to exactly identical treatment. +Yet this test is one of the most important made on wood, as it +brings out properties not evident from other tests. Defects and +brittleness are revealed by impact better than by any other kind +of test. In common practice nearly all external stresses are of +the nature of impact. In fact, no two moving bodies can come +together without impact stress. Impact is therefore the +commonest form of applied stress, although the most difficult to +measure. + +<h4><i>Failures in Timber Beams</i></h4> + +<p>If a beam is loaded too heavily it will break or fail in some +characteristic manner. These failures may be classified +according to the way in which they develop, as tension, +compression, and horizontal shear; and according to the +appearance of the broken surface, as brash, and fibrous. A +number of forms may develop if the beam is completely ruptured.</p> + +<p>Since the tensile strength of wood is on the average about three +times as great as the compressive strength, a beam should, +therefore, be expected to fail by the formation in the first +place of a fold on the compression side due to the crushing +action, followed by failure on the tension side. This is usually +the case in green or moist wood. In dry material the first +visible failure is not infrequently on the lower or tension +side, and various attempts have been made to explain why such is +the case.<a name="fn15r"></a><a href="#fn15"><sup><small>15</small></sup></a></p> + +<p>Within the elastic limit the elongations and shortenings are +equal, and the neutral plane lies in the middle of the beam. +(<a href="#pg023">See page 23</a>.) Later the +top layer of fibres on the upper or compression side fail, and +on the load increasing, the next layer of fibres fail, and so +on, even though this failure may not be visible. As a result the +shortenings on the upper side of the beam become considerably +greater than the elongations on the lower side. The neutral +plane must be presumed to sink gradually toward the tension +side, and when the stresses on the outer fibres at the bottom +<a name="pg034"></a> +have become sufficiently great, the fibres are pulled in two, +the tension area being much smaller than the compression area. +The rupture is often irregular, as in direct tension tests. +Failure may occur partially in single bundles of fibres some +time before the final failure takes place. One reason why the +failure of a dry beam is different from one that is moist, is +that drying increases the stiffness of the fibres so that they +offer more resistance to crushing, while it has much less effect +upon the tensile strength.</p> + +<p>There is considerable variation in tension failures depending +upon the toughness or the brittleness of the wood, the +arrangement of the grain, defects, etc., making further +classification desirable. The four most common forms are:</p> + +<p>(1) <b>Simple tension,</b> in which there is a direct pulling in two +of the wood on the under side of the beam due to a tensile +stress parallel to the grain, (<a href="#fig17">See Fig. 17</a>, No. 1.) This is +common in straight-grained beams, particularly when the wood is +seasoned.</p> + +<p>(2) <b>Cross-grained tension,</b> in which the fracture is caused by a +tensile force acting oblique to the grain. (<a href="#fig17">See Fig. 17</a>, No. 2.) +This is a common form of failure where the beam has diagonal, +spiral or other form of cross grain on its lower side. Since the +tensile strength of wood across the grain is only a small +fraction of that with the grain it is easy to see why a +cross-grained timber would fail in this manner.</p> + +<p>(3) <b>Splintering tension,</b> in which the failure consists of a +considerable number of slight tension failures, producing a +ragged or splintery break on the under surface of the beam. (<a href="#fig17">See +Fig. 17</a>, No. 3.) This is common in tough woods. In this case the +surface of fracture is fibrous.</p> + +<p>(4) <b>Brittle tension,</b> in which the beam fails by a clean break +extending entirely through it. (<a href="#fig17">See Fig. 17</a>, No. 4.) It is +characteristic of a brittle wood which gives way suddenly +without warning, like a piece of chalk. In this case the surface +of fracture is described as brash.</p> + +<p><b>Compression failure</b> (<a href="#fig17">see Fig. 17</a>, No. 5) has few variations +except that it appears at various distances from the neutral +plane of the beam. It is very common in green timbers. The +compressive stress parallel to the fibres causes them to buckle +or bend as in an endwise compressive test. This action usually +<a name="pg035"></a> +begins on the top side shortly after the elastic limit is +reached and extends downward, sometimes almost reaching the +neutral plane before complete failure occurs. Frequently two or +more failures develop at about the same time.</p> + +<p class="ctr"><img src="images/fig17.jpg" alt="Figure 17" id="fig17" /></p> +<p class="imgtitle">Figure 17</p> +<p class="imgtext"> Characteristic failures of simple beams.</p> + +<p><b>Horizontal shear failure,</b> in which the upper and lower +portions of the beam slide along each other for a portion of +their length either at one or at both ends (<a href="#fig17">see Fig. 17</a>, No. 6), +is fairly common in air-dry material and in green material when +the ratio of the height of the beam to the span is relatively +large. It is not common in small clear specimens. It is often +due to shake or season checks, common in large timbers, which +<a name="pg036"></a> +reduce the actual area resisting the shearing action +considerably below the calculated area used in the formulæ for +horizontal shear. (<a href="#pg098">See page 98</a> for this formulæ.) For this +reason it is unsafe, in designing large timber beams, to use +shearing stresses higher than those calculated for beams that +failed in horizontal shear. The effect of a failure in +horizontal shear is to divide the beam into two or more beams +the combined strength of which is much less than that of the +original beam. <a href="#fig18">Fig. 18</a> shows a large beam in which two failures +<a name="pg037"></a> +in horizontal shear occurred at the same end. That the parts +behave independently is shown by the compression failure below +the original location of the neutral plane.</p> + +<p class="ctr"><img src="images/fig18.jpg" alt="Figure 18" id="fig18" /></p> +<p class="imgtitle">Figure 18</p> +<p class="imgtext"> Failure of a large beam by horizontal shear. <i>Photo by U. S, Forest Service</i>.</p> + +<p>Table XI gives an analysis of the causes of first failure in 840 +large timber beams of nine different species of conifers. Of the +total number tested 165 were air-seasoned, the remainder green. +The failure occurring first signifies the point of greatest +weakness in the specimen under the particular conditions of +loading employed (in this case, third-point static loading).</p> + +<center> +<table id="TABLE_11" summary="TABLE_XI" border="3" cellspacing="0" cellpadding="1" width="40%"> +<tbody> +<tr><th colspan="5"> TABLE XI </th></tr> +<tr><th colspan="5"> MANNER OF FIRST FAILURE OF LARGE BEAMS </th></tr> +<tr><td colspan="5"> (Forest Service Bul. 108, p. 56) </td></tr> +<tr><th rowspan="2"> COMMON NAME OF SPECIES </th> <th rowspan="2"> Total number of tests </th> + <th colspan="3"> Per cent of total failing by </th></tr> + <tr><th> Tension </th> + <th> Compression </th> + <th> Shear </th></tr> +<tr><th style="text-align: left;"> Longleaf pine: </th> <td><br></td> <td><br></td><td><br></td><td><br></td></tr> +<tr><td style="text-align: left;"> green</td><td> 17 </td> <td> 18 </td><td> 24 </td><td> 58 </td></tr> +<tr><td style="text-align: left;"> dry</td> <td> 9 </td> <td> 22 </td><td> 22 </td><td> 56 </td></tr> +<tr><th style="text-align: left;"> Douglas fir: </th> <td><br></td> <td><br></td><td><br></td><td><br></td></tr> +<tr><td style="text-align: left;"> green</td><td> 191 </td><td> 27 </td><td> 72 </td><td> 1 </td></tr> +<tr><td style="text-align: left;"> dry</td> <td> 91 </td> <td> 19 </td><td> 76 </td><td> 5 </td></tr> +<tr><th style="text-align: left;"> Shortleaf pine: </th> <td><br></td> <td><br></td><td><br></td><td><br></td></tr> +<tr><td style="text-align: left;"> green</td><td> 48 </td> <td> 27 </td><td> 56 </td><td> 17 </td></tr> +<tr><td style="text-align: left;"> dry</td> <td> 13 </td> <td> 54 </td><td><br></td><td> 46 </td></tr> +<tr><th style="text-align: left;"> Western larch: </th> <td><br></td> <td><br></td><td><br></td><td><br></td></tr> +<tr><td style="text-align: left;"> green</td><td> 62 </td> <td> 23 </td><td> 71 </td><td> 6 </td></tr> +<tr><td style="text-align: left;"> dry</td> <td> 52 </td> <td> 54 </td><td> 19 </td><td> 27 </td></tr> +<tr><th style="text-align: left;"> Loblolly pine: </th> <td><br></td> <td><br></td><td><br></td><td><br></td></tr> +<tr><td style="text-align: left;"> green</td><td> 111 </td><td> 40 </td><td> 53 </td><td> 7 </td></tr> +<tr><td style="text-align: left;"> dry</td> <td> 25 </td> <td> 60 </td><td> 12 </td><td> 28 </td></tr> +<tr><th style="text-align: left;"> Tamarack: </th> <td><br></td> <td><br></td><td><br></td><td><br></td></tr> +<tr><td style="text-align: left;"> green</td><td> 30 </td> <td> 37 </td><td> 53 </td><td> 10 </td></tr> +<tr><td style="text-align: left;"> dry</td> <td> 9 </td> <td> 45 </td><td> 22 </td><td> 33 </td></tr> +<tr><th style="text-align: left;"> Western hemlock: </th><td><br></td> <td><br></td><td><br></td><td><br></td></tr> +<tr><td style="text-align: left;"> green</td><td> 39 </td> <td> 21 </td><td> 74 </td><td> 5 </td></tr> +<tr><td style="text-align: left;"> dry</td> <td> 44 </td> <td> 11 </td><td> 66 </td><td> 23 </td></tr> +<tr><th style="text-align: left;"> Redwood: </th> <td><br></td> <td><br></td><td><br></td><td><br></td></tr> +<tr><td style="text-align: left;"> green</td><td> 28 </td> <td> 43 </td><td> 50 </td><td> 7 </td></tr> +<tr><td style="text-align: left;"> dry</td> <td> 12 </td> <td> 83 </td><td> 17 </td><td><br></td></tr> +<tr><th style="text-align: left;"> Norway pine: </th> <td><br></td> <td><br></td><td><br></td><td><br></td></tr> +<tr><td style="text-align: left;"> green</td><td> 49 </td> <td> 18 </td><td> 76 </td><td> 6 </td></tr> +<tr><td style="text-align: left;"> dry</td> <td> 10 </td> <td> 30 </td><td> 60 </td><td> 10 </td></tr> +<tr><td style="text-align: left;" colspan="5"> NOTE.—These tests were made on timbers ranging in cross section from 4" × 10" to 8" × 16", and with a span of 15 feet. </td></tr> +</tbody> +</table> +</center> + +<a name="I_07"></a> +<h3>TOUGHNESS: TORSION</h3> + +<p>Toughness is a term applied to more than one property of wood. +Thus wood that is difficult to split is said to be tough. Again, +a tough wood is one that will not rupture until it has deformed +considerably under loads at or near its maximum strength, or one +which still hangs together after it has been ruptured and may be +bent back and forth without breaking apart. Toughness includes +flexibility and is the reverse of brittleness, in that tough +woods <a name="pg038"></a> break gradually and give warning of failure. Tough woods +offer great resistance to impact and will permit rougher +treatment in manipulations attending manufacture and use. +Toughness is dependent upon the strength, cohesion, quality, +length, and arrangement of fibre, and the pliability of the +wood. Coniferous woods as a rule are not as tough as hardwoods, +of which hickory and elm are the best examples.</p> + +<p class="ctr"><img src="images/fig19.jpg" alt="Figure 19" id="fig19" /></p> +<p class="imgtitle">Figure 19</p> +<p class="imgtext"> Torsion of a shaft.</p> + +<p>The torsion or twisting test is useful in determining the +toughness of wood. If the ends of a shaft are turned in opposite +directions, or one end is turned and the other is fixed, all of +the fibres except those at the axis tend to assume the form of +helices. (<a href="#fig19">See Fig. 19</a>.) The strain produced by torsion or +twisting is essentially shear transverse and parallel to the +fibres, combined with longitudinal tension and transverse +compression. Within the elastic limit the strains increase +directly as the distance from the axis of the specimen. The +outer elements are subjected to tensile stresses, and as they +become twisted tend to compress those near the axis. The +elongated elements also contract laterally. Cross sections which +were originally plane become warped. With increasing strain the +lateral adhesion of the outer fibres is destroyed, allowing them +to slide past each other, and reducing greatly their power of +resistance. In this way the strains on the fibres nearer the +axis are progressively increased until finally all of the +elements are sheared apart. It is only in the toughest materials +that the full effect of this action can be observed. (<a href="#fig20">See Fig. +20</a>.) Brittle woods snap off suddenly with only a small amount of +torsion, and their fracture is irregular and oblique <a name="pg039"></a> to the axis +of the piece instead of frayed out and more nearly perpendicular +to the axis as is the case with tough woods.</p> + +<p class="ctr"><img src="images/fig20.jpg" alt="Figure 20" id="fig20" /></p> +<p class="imgtitle">Figure 20</p> +<p class="imgtext"> Effect of torsion on different grades of hickory. <i>Photo by U. S. Forest Service.</i></p> + +<a name="I_08"></a> +<h3>HARDNESS</h3> + +<p>The term <i>hardness</i> is used in two senses, namely: (1) +resistance to indentation, and (2) resistance to abrasion or +scratching. In the latter sense hardness combined with toughness +is a measure of the wearing ability of wood and is an important +consideration in the use of wood for floors, paving blocks, +bearings, and rollers. While resistance to indentation is +dependent mostly upon the density of the wood, the wearing +qualities may be governed by other factors such as toughness, +and the size, cohesion, and arrangement of the fibres. In use +for floors, some woods tend to compact and wear smooth, while +others become splintery and rough. This feature is affected to +some extent by the manner in which the wood is sawed; thus +edge-grain pine flooring is much better than flat-sawn for +uniformity of wear.</p> + +<a name="pg040"></a> + +<center> +<table id="TABLE_12" summary="TABLE_XII" border="3" cellspacing="0" cellpadding="1" width="60%"> +<tbody> +<tr><th colspan="5"> TABLE XII </th></tr> +<tr><th colspan="5"> HARDNESS OF 32 WOODS IN GREEN CONDITION, AS INDICATED BY THE LOAD REQUIRED TO IMBED A 0.444-INCH STEEL BALL TO ONE-HALF ITS DIAMETER </th></tr> +<tr><td colspan="5"> (Forest Service Cir. 213) </td></tr> +<tr><th rowspan="2"> COMMON NAME OF SPECIES </th> <th> Average </th> + <th> End surface </th> + <th> Radial surface </th> + <th> Tangential surface </th></tr> + <tr><th><i>Pounds</i></th> + <th><i>Pounds</i></th> + <th><i>Pounds</i></th> + <th><i>Pounds</i></th></tr> +<tr><th> <i>Hardwoods</i> </th> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> 1 Osage orange</td> <td> 1,971 </td><td> 1,838 </td><td> 2,312 </td><td> 1,762 </td></tr> +<tr><td style="text-align: left;"> 2 Honey locust</td> <td> 1,851 </td><td> 1,862 </td><td> 1,860 </td><td> 1,832 </td></tr> +<tr><td style="text-align: left;"> 3 Swamp white oak</td> <td> 1,174 </td><td> 1,205 </td><td> 1,217 </td><td> 1,099 </td></tr> +<tr><td style="text-align: left;"> 4 White oak</td> <td> 1,164 </td><td> 1,183 </td><td> 1,163 </td><td> 1,147 </td></tr> +<tr><td style="text-align: left;"> 5 Post oak</td> <td> 1,099 </td><td> 1,139 </td><td> 1,068 </td><td> 1,081 </td></tr> +<tr><td style="text-align: left;"> 6 Black oak</td> <td> 1,069 </td><td> 1,093 </td><td> 1,083 </td><td> 1,031 </td></tr> +<tr><td style="text-align: left;"> 7 Red oak</td> <td> 1,043 </td><td> 1,107 </td><td> 1,020 </td><td> 1,002 </td></tr> +<tr><td style="text-align: left;"> 8 White ash</td> <td> 1,046 </td><td> 1,121 </td><td> 1,000 </td><td> 1,017 </td></tr> +<tr><td style="text-align: left;"> 9 Beech</td> <td> 942 </td> <td> 1,012 </td><td> 897 </td> <td> 918 </td></tr> +<tr><td style="text-align: left;"> 10 Sugar maple</td> <td> 937 </td> <td> 992 </td> <td> 918 </td> <td> 901 </td></tr> +<tr><td style="text-align: left;"> 11 Rock elm</td> <td> 910 </td> <td> 954 </td> <td> 883 </td> <td> 893 </td></tr> +<tr><td style="text-align: left;"> 12 Hackberry</td> <td> 799 </td> <td> 829 </td> <td> 795 </td> <td> 773 </td></tr> +<tr><td style="text-align: left;"> 13 Slippery elm</td> <td> 788 </td> <td> 919 </td> <td> 757 </td> <td> 687 </td></tr> +<tr><td style="text-align: left;"> 14 Yellow birch</td> <td> 778 </td> <td> 827 </td> <td> 768 </td> <td> 739 </td></tr> +<tr><td style="text-align: left;"> 15 Tupelo</td> <td> 738 </td> <td> 814 </td> <td> 666 </td> <td> 733 </td></tr> +<tr><td style="text-align: left;"> 16 Red maple</td> <td> 671 </td> <td> 766 </td> <td> 621 </td> <td> 626 </td></tr> +<tr><td style="text-align: left;"> 17 Sycamore</td> <td> 608 </td> <td> 664 </td> <td> 560 </td> <td> 599 </td></tr> +<tr><td style="text-align: left;"> 18 Black ash</td> <td> 551 </td> <td> 565 </td> <td> 542 </td> <td> 546 </td></tr> +<tr><td style="text-align: left;"> 19 White elm</td> <td> 496 </td> <td> 536 </td> <td> 456 </td> <td> 497 </td></tr> +<tr><td style="text-align: left;"> 20 Basswood</td> <td> 239 </td> <td> 273 </td> <td> 226 </td> <td> 217 </td></tr> +<tr><th> <i>Conifers</i> </th> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> 1 Longleaf pine</td> <td> 532 </td> <td> 574 </td> <td> 502 </td> <td> 521 </td></tr> +<tr><td style="text-align: left;"> 2 Douglas fir</td> <td> 410 </td> <td> 415 </td> <td> 399 </td> <td> 416 </td></tr> +<tr><td style="text-align: left;"> 3 Bald cypress</td> <td> 390 </td> <td> 460 </td> <td> 355 </td> <td> 354 </td></tr> +<tr><td style="text-align: left;"> 4 Hemlock</td> <td> 384 </td> <td> 463 </td> <td> 354 </td> <td> 334 </td></tr> +<tr><td style="text-align: left;"> 5 Tamarack</td> <td> 384 </td> <td> 401 </td> <td> 380 </td> <td> 370 </td></tr> +<tr><td style="text-align: left;"> 6 Red pine</td> <td> 347 </td> <td> 355 </td> <td> 345 </td> <td> 340 </td></tr> +<tr><td style="text-align: left;"> 7 White fir</td> <td> 346 </td> <td> 381 </td> <td> 322 </td> <td> 334 </td></tr> +<tr><td style="text-align: left;"> 8 Western yellow pine</td><td> 328 </td> <td> 334 </td> <td> 307 </td> <td> 342 </td></tr> +<tr><td style="text-align: left;"> 9 Lodgepole pine</td> <td> 318 </td> <td> 316 </td> <td> 318 </td> <td> 319 </td></tr> +<tr><td style="text-align: left;"> 10 White pine</td> <td> 299 </td> <td> 304 </td> <td> 294 </td> <td> 299 </td></tr> +<tr><td style="text-align: left;"> 11 Engelmann pine</td> <td> 266 </td> <td> 272 </td> <td> 253 </td> <td> 274 </td></tr> +<tr><td style="text-align: left;"> 12 Alpine fir</td> <td> 241 </td> <td> 284 </td> <td> 203 </td> <td> 235 </td></tr> +<tr><td style="text-align: left;" colspan="5"> NOTE.—Black locust and hickory are not included in this table, but their position would be near the head of the list. </td></tr> +</tbody> +</table> +</center> + +<a name="pg041"></a> + +<p>Tests for either form of hardness are of comparative value only. +Tests for indentation are commonly made by penetrations of the +material with a steel punch or ball.<a name="fn16r"></a><a href="#fn16"><sup><small>16</small></sup></a> Tests for abrasion are +made by wearing down wood with sandpaper or by means of a sand +blast.</p> + +<a name="I_09"></a> +<h3>CLEAVABILITY</h3> + +<p><i>Cleavability</i> is the term used to denote the facility with +which wood is split. A splitting stress is one in which the +forces act normally like a wedge. (<a href="#fig21">See Fig. 21</a>.) The plane of +cleavage is parallel to the grain, either radially or +tangentially.</p> + +<p class="ctr"><img src="images/fig21.jpg" alt="Figure 21" id="fig21" /></p> +<p class="imgtitle">Figure 21</p> +<p class="imgtext"> Cleavage of highly elastic wood. The cleft runs far ahead of the wedge.</p> + +<p>This property of wood is very important in certain uses such as +firewood, fence rails, billets, and squares. Resistance to +splitting or low cleavability is desirable where wood must hold +nails or screws, as in box-making. Wood usually splits more +readily along the radius than parallel to the growth rings +though exceptions occur, as in the case of cross grain.</p> + +<p>Splitting involves transverse tension, but only a portion of the +fibres are under stress at a time. A wood of little stiffness +and strong cohesion across the grain is difficult to split, +while one with great stiffness, such as longleaf pine, is easily +split. The form of the grain and the presence of knots greatly +affect this quality.</p> + +<a name="pg042"></a> + +<center> +<table id="TABLE_13" summary="TABLE_XIII" border="3" cellspacing="0" cellpadding="1" width="60%"> +<tbody> +<tr><th colspan="3"> TABLE XIII </th></tr> +<tr><th colspan="3"> CLEAVAGE STRENGTH OF SMALL CLEAR PIECES OF 32 WOODS IN GREEN CONDITION </th></tr> +<tr><td colspan="3"> (Forest Service Cir. 213) </td></tr> +<tr><th rowspan="2"> COMMON NAME OF SPECIES </th> <th> When surface of failure is radial </th> + <th> When surface of failure is tangential </th></tr> +<tr> <th><i>Lbs. per sq. inch</i></th> + <th><i>Lbs. per sq. inch</i></th></tr> +<tr><th> <i>Hardwoods</i> </th> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Ash, black</td> <td> 275 </td><td> 260 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 333 </td><td> 346 </td></tr> +<tr><td style="text-align: left;"> Bashwood </td> <td> 130 </td><td> 168 </td></tr> +<tr><td style="text-align: left;"> Beech </td> <td> 339 </td><td> 527 </td></tr> +<tr><td style="text-align: left;"> Birch, yellow </td> <td> 294 </td><td> 287 </td></tr> +<tr><td style="text-align: left;"> Elm, slippery </td> <td> 401 </td><td> 424 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 210 </td><td> 270 </td></tr> +<tr><td style="text-align: left;"> Hackberr </td> <td> 422 </td><td> 436 </td></tr> +<tr><td style="text-align: left;"> Locust, honey </td> <td> 552 </td><td> 610 </td></tr> +<tr><td style="text-align: left;"> Maple, red </td> <td> 297 </td><td> 330 </td></tr> +<tr><td style="text-align: left;"> sugar </td> <td> 376 </td><td> 513 </td></tr> +<tr><td style="text-align: left;"> Oak, post </td> <td> 354 </td><td> 487 </td></tr> +<tr><td style="text-align: left;"> red </td> <td> 380 </td><td> 470 </td></tr> +<tr><td style="text-align: left;"> swamp white </td> <td> 428 </td><td> 536 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 382 </td><td> 457 </td></tr> +<tr><td style="text-align: left;"> yellow </td> <td> 379 </td><td> 470 </td></tr> +<tr><td style="text-align: left;"> Sycamore </td> <td> 265 </td><td> 425 </td></tr> +<tr><td style="text-align: left;"> Tupelo </td> <td> 277 </td><td> 380 </td></tr> +<tr><th> <i>Conifers</i> </th> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Arborvitæ </td> <td> 148 </td><td> 139 </td></tr> +<tr><td style="text-align: left;"> Cypress, bald </td> <td> 167 </td><td> 154 </td></tr> +<tr><td style="text-align: left;"> Fir, alpine </td> <td> 130 </td><td> 133 </td></tr> +<tr><td style="text-align: left;"> Douglas </td> <td> 139 </td><td> 127 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 145 </td><td> 187 </td></tr> +<tr><td style="text-align: left;"> Hemlock </td> <td> 168 </td><td> 151 </td></tr> +<tr><td style="text-align: left;"> Pine, lodgepole </td> <td> 142 </td><td> 140 </td></tr> +<tr><td style="text-align: left;"> longleaf </td> <td> 187 </td><td> 180 </td></tr> +<tr><td style="text-align: left;"> red </td> <td> 161 </td><td> 154 </td></tr> +<tr><td style="text-align: left;"> sugar </td> <td> 168 </td><td> 189 </td></tr> +<tr><td style="text-align: left;"> western yellow </td><td> 162 </td><td> 187 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 144 </td><td> 160 </td></tr> +<tr><td style="text-align: left;"> Spruce, Engelmann </td> <td> 110 </td><td> 135 </td></tr> +<tr><td style="text-align: left;"> Tamarack </td> <td> 167 </td><td> 159 </td></tr> + </tbody> +</table> +</center> + +<a name="pg043"></a> +<a name="PART_II"></a> +<h2>PART II<br>FACTORS AFFECTING THE MECHANICAL PROPERTIES OF WOOD</h2> + +<a name="II_01"></a> +<h3>INTRODUCTION</h3> + +<p>Wood is an organic product—a structure of infinite variation of +detail and design.<a name="fn17r"></a><a href="#fn17"><sup><small>17</small></sup></a> It is on this account that no two woods +are alike—in reality no two specimens from the same log are +identical. There are certain properties that characterize each +species, but they are subject to considerable variation. Oak, +for example, is considered hard, heavy, and strong, but some +pieces, even of the same species of oak, are much harder, +heavier, and stronger than others. With hickory are associated +the properties of great strength, toughness, and resilience, but +some pieces are comparatively weak and brash and ill-suited for +the exacting demands for which good hickory is peculiarly +adapted.</p> + +<p>It follows that no definite value can be assigned to the +properties of any wood and that tables giving average results of +tests may not be directly applicable to any individual stick. +With sufficient knowledge of the intrinsic factors affecting the +results it becomes possible to infer from the appearance of +material its probable variation from the average. As yet too +little is known of the relation of structure and chemical +composition to the mechanical and physical properties to permit +more than general conclusions. + +<a name="II_02"></a> +<h3>RATE OF GROWTH</h3> + +<p>To understand the effect of variations in the rate of growth it +is first necessary to know how wood is formed. A tree increases +in diameter by the formation, between the old wood and the inner +bark, of new woody layers which envelop the entire stem, living +<a name="pg044"></a> +branches, and roots. Under ordinary conditions one layer is +formed each year and in cross section as on the end of a log +they appear as rings—often spoken of as <i>annual rings</i>. These +growth layers are made up of wood cells of various kinds, but +for the most part fibrous. In timbers like pine, spruce, +hemlock, and other coniferous or softwood species the wood cells +are mostly of one kind, and as a result the material is much +more uniform in structure than that of most hardwoods. (<a href="#fig00">See +Frontispiece</a>.) There are no vessels or pores in coniferous wood +such as one sees so prominently in oak and ash, for example. +(<a href="#fig22">See Fig. 22</a>.)</p> + +<p class="ctr"><img src="images/fig22.jpg" alt="Figure 22" id="fig22" /></p> +<p class="imgtitle">Figure 22</p> +<p class="imgtext"> Cross sections of a ring-porous +hardwood (white ash), a diffuse-porous hardwood (red gum), and a +non-porous or coniferous wood (eastern hemlock). × 30. +<i>Photomicrographs by the author.</i></p> + +<p>The structure of the hardwoods is more complex. They are more or +less filled with vessels, in some cases (oak, chestnut, ash) +quite large and distinct, in others (buckeye, poplar, gum) too +small to be seen plainly without a small hand lens. In +discussing such woods it is customary to divide them into two +large classes—<i>ring-porous</i> and <i>diffuse-porous</i>. (<a href="#fig22">See Fig. +22</a>.) In ring-porous species, such as oak, chestnut, ash, black +locust, catalpa, mulberry, hickory, and elm, the larger vessels +or pores (as cross sections of vessels are called) become +localized in one part of the growth ring, thus forming a region +of more or less open and porous tissue. The rest of the ring is +made up of smaller vessels and a much greater proportion of wood +fibres. These fibres are the elements which give strength and +toughness to wood, while the vessels are a source of weakness.</p> + +<p>In diffuse-porous woods the pores are scattered throughout the +growth ring instead of being collected in a band or row. +Examples of this kind of wood are gum, yellow poplar, birch, +maple, cottonwood, basswood, buckeye, and willow. Some species, +such as walnut and cherry, are on the border between the two +classes, forming a sort of intermediate group.</p> + +<p>If one examines the smoothly cut end of a stick of almost any +kind of wood, he will note that each growth ring is made up of +two more or less well-defined parts. That originally nearest the +centre of the tree is more open textured and almost invariably +lighter in color than that near the outer portion of the ring. +The inner portion was formed early in the season, when growth +was comparatively rapid and is known as <i>early wood</i> (also +spring wood); the outer portion is the <i>late wood</i>, being +produced in the <a name="pg045"></a> summer or early fall. In soft pines there is not +much contrast in the different parts of the ring, and as a +result the wood is very uniform in texture and is easy to work. +In hard pine, on the other hand, the late wood is very dense and +is deep-colored, presenting a very decided contrast to the soft, +straw-colored early wood. (<a href="#fig23">See Fig. 23</a>.) In ring-porous woods +each season's growth is always well defined, because the large +pores of the spring abut on the denser tissue of the fall +before. In the diffuse-porous, the demarcation between rings is +not always so clear and in not a few <a name="pg046"></a> cases is almost, if not +entirely, invisible to the unaided eye. (<a href="#fig22">See Fig. 22</a>.)</p> + +<p class="ctr"><img src="images/fig23.jpg" alt="Figure 23" id="fig23" /></p> +<p class="imgtitle">Figure 23</p> +<p class="imgtext"> Cross section of longleaf pine showing +several growth rings with variations in the width of the +dark-colored late wood. Seven resin ducts are visible. × 33. +<i>Photomicrograph by U.S. Forest Service</i>.</p> + +<p>If one compares a heavy piece of pine with a light specimen it +will be seen at once that the heavier one contains a larger +proportion of late wood than the other, and is therefore +considerably darker. The late wood of all species is denser than +that formed early in the season, hence the greater the +<a name="pg047"></a> +proportion of late wood the greater the density and strength. +When examined under a microscope the cells of the late wood are +seen to be very thick-walled and with very small cavities, while +those formed first in the season have thin walls and large +cavities. The strength is in the walls, not the cavities. In +choosing a piece of pine where strength or stiffness is the +important consideration, the principal thing to observe is the +comparative amounts of early and late wood. The width of ring, +that is, the number per inch, is not nearly so important as the +proportion of the late wood in the ring.</p> + +<p>It is not only the proportion of late wood, but also its +quality, that counts. In specimens that show a very large +proportion of late wood it may be noticeably more porous and +weigh considerably less than the late wood in pieces that +contain but little. One can judge comparative density, and +therefore to some extent weight and strength, by visual +inspection.</p> + +<p>The conclusions of the U.S. Forest Service regarding the effect +of rate of growth on the properties of Douglas fir are +summarized as follows:</p> + +<p>"1. In general, rapidly grown wood (less than eight rings per +inch) is relatively weak. A study of the individual tests upon +which the average points are based shows, however, that when it +is not associated with light weight and a small proportion of +summer wood, rapid growth is not indicative of weak wood.</p> + +<p>"2. An average rate of growth, indicated by from 12 to 16 rings +per inch, seems to produce the best material.</p> + +<p>"3. In rates of growths lower than 16 rings per inch, the +average strength of the material decreases, apparently +approaching a uniform condition above 24 rings per inch. In such +slow rates of growth the texture of the wood is very uniform, +and naturally there is little variation in weight or strength.</p> + +<p>"An analysis of tests on large beams was made to ascertain if +average rate of growth has any relation to the mechanical +properties of the beams. The analysis indicated conclusively +that there was no such relation. Average rate of growth [without +consideration also of density], therefore, has little +significance in <a name="pg048"></a> grading structural timber."<a name="fn18r"></a><a href="#fn18"><sup><small>18</small></sup></a> This is because +of the wide variation in the percentage of late wood in +different parts of the cross section.</p> + +<p>Experiments seem to indicate that for most species there is a +rate of growth which, in general, is associated with the +greatest strength, especially in small specimens. For eight +conifers it is as follows:<a name="fn19r"></a><a href="#fn19"><sup><small>19</small></sup></a></p> + +<center> +<table summary="text"> +<tbody> +<tr><td><br></td> <td>Rings per inch</td></tr> +<tr><td style="text-align: left;"> Douglas fir </td> <td>24</td></tr> +<tr><td style="text-align: left;"> Shortleaf pine </td> <td>12</td></tr> +<tr><td style="text-align: left;"> Loblolly pine </td> <td>6</td></tr> +<tr><td style="text-align: left;"> Western larch </td> <td>18</td></tr> +<tr><td style="text-align: left;"> Western hemlock </td><td>14</td></tr> +<tr><td style="text-align: left;"> Tamarack </td> <td>20</td></tr> +<tr><td style="text-align: left;"> Norway pine </td> <td>18</td></tr> +<tr><td style="text-align: left;"> Redwood </td> <td>30</td></tr> +</tbody> +</table> +</center> + +<p>No satisfactory explanation can as yet be given for the real +causes underlying the formation of early and late wood. Several +factors may be involved. In conifers, at least, rate of growth +alone does not determine the proportion of the two portions of +the ring, for in some cases the wood of slow growth is very hard +and heavy, while in others the opposite is true. The quality of +the site where the tree grows undoubtedly affects the character +of the wood formed, though it is not possible to formulate a +rule governing it. In general, however, it may be said that +where strength or ease of working is essential, woods of +moderate to slow growth should be chosen. But in choosing a +particular specimen it is not the width of ring, but the +proportion and character of the late wood which should govern.</p> + +<p>In the case of the ring-porous hardwoods there seems to exist a +pretty definite relation between the rate of growth of timber +and its properties. This may be briefly summed up in the general +statement that the more rapid the growth or the wider the rings +of growth, the heavier, harder, stronger, and stiffer the wood. +This, it must be remembered, applies only to ring-porous woods +such as oak, ash, hickory, and others of the same group, and is, +of course, subject to some exceptions and limitations.</p> + +<p>In ring-porous woods of good growth it is usually the middle +<a name="pg049"></a> +portion of the ring in which the thick-walled, strength-giving +fibres are most abundant. As the breadth of ring diminishes, +this middle portion is reduced so that very slow growth produces +comparatively light, porous wood composed of thin-walled vessels +and wood parenchyma. In good oak these large vessels of the +early wood occupy from 6 to 10 per cent of the volume of the +log, while in inferior material they may make up 25 per cent or +more. The late wood of good oak, except for radial grayish +patches of small pores, is dark colored and firm, and consists +of thick-walled fibres which form one-half or more of the wood. +In inferior oak, such fibre areas are much reduced both in +quantity and quality. Such variation is very largely the result +of rate of growth.</p> + +<p>Wide-ringed wood is often called "second-growth," because the +growth of the young timber in open stands after the old trees +have been removed is more rapid than in trees in the forest, and +in the manufacture of articles where strength is an important +consideration such "second-growth" hardwood material is +preferred. This is particularly the case in the choice of +hickory for handles and spokes. Here not only strength, but +toughness and resilience are important. The results of a series +of tests on hickory by the U.S. Forest Service show that "the +work or shock-resisting ability is greatest in wide-ringed wood +that has from 5 to 14 rings per inch, is fairly constant from 14 +to 38 rings, and decreases rapidly from 38 to 47 rings. The +strength at maximum load is not so great with the most +rapid-growing wood; it is maximum with from 14 to 20 rings per +inch, and again becomes less as the wood becomes more closely +ringed. The natural deduction is that wood of first-class +mechanical value shows from 5 to 20 rings per inch and that +slower growth yields poorer stock. Thus the inspector or buyer +of hickory should discriminate against timber that has more than +20 rings per inch. Exceptions exist, however, in the case of +normal growth upon dry situations, in which the slow-growing +material may be strong and tough."<a name="fn20r"></a><a href="#fn20"><sup><small>20</small></sup></a></p> + +<p>The effect of rate of growth on the qualities of chestnut wood +is summarized by the same authority as follows: "When the rings +are wide, the transition from spring wood to summer wood <a name="pg050"></a> is +gradual, while in the narrow rings the spring wood passes into +summer wood abruptly. The width of the spring wood changes but +little with the width of the annual ring, so that the narrowing +or broadening of the annual ring is always at the expense of the +summer wood. The narrow vessels of the summer wood make it +richer in wood substance than the spring wood composed of wide +vessels. Therefore, rapid-growing specimens with wide rings have +more wood substance than slow-growing trees with narrow rings. +Since the more the wood substance the greater the weight, and +the greater the weight the stronger the wood, chestnuts with +wide rings must have stronger wood than chestnuts with narrow +rings. This agrees with the accepted view that sprouts (which +always have wide rings) yield better and stronger wood than +seedling chestnuts, which grow more slowly in diameter."<a name="fn21r"></a><a href="#fn21"><sup><small>21</small></sup></a></p> + +<p>In diffuse-porous woods, as has been stated, the vessels or +pores are scattered throughout the ring instead of collected in +the early wood. The effect of rate of growth is, therefore, not +the same as in the ring-porous woods, approaching more nearly +the conditions in the conifers. In general it may be stated that +such woods of medium growth afford stronger material than when +very rapidly or very slowly grown. In many uses of wood, +strength is not the main consideration. If ease of working is +prized, wood should be chosen with regard to its uniformity of +texture and straightness of grain, which will in most cases +occur when there is little contrast between the late wood of one +season's growth and the early wood of the next.</p> + +<a name="II_03"></a> +<h3>HEARTWOOD AND SAPWOOD</h3> + +<p>Examination of the end of a log of many species reveals a +darker-colored inner portion—the <i>heartwood</i>, surrounded by a +lighter-colored zone—the <i>sapwood</i>. In some instances this +distinction in color is very marked; in others, the contrast is +slight, so that it is not always easy to tell where one leaves +off and the other begins. The color of fresh sapwood is always +light, sometimes pure white, but more often with a decided tinge +of green or brown.</p> + +<a name="pg051"></a> + +<p>Sapwood is comparatively new wood. There is a time in the early +history of every tree when its wood is all sapwood. Its +principal functions are to conduct water from the roots to the +leaves and to store up and give back according to the season the +food prepared in the leaves. The more leaves a tree bears and +the more thrifty its growth, the larger the volume of sapwood +required, hence trees making rapid growth in the open have +thicker sapwood for their size than trees of the same species +growing in dense forests. Sometimes trees grown in the open may +become of considerable size, a foot or more in diameter, before +any heartwood begins to form, for example, in second-growth +hickory, or field-grown white and loblolly pines.</p> + +<p>As a tree increases in age and diameter an inner portion of the +sapwood becomes inactive and finally ceases to function. This +inert or dead portion is called heartwood, deriving its name +solely from its position and not from any vital importance to +the tree, as is shown by the fact that a tree can thrive with +its heart completely decayed. Some, species begin to form +heartwood very early in life, while in others the change comes +slowly. Thin sapwood is characteristic of such trees as +chestnut, black locust, mulberry, Osage orange, and sassafras, +while in maple, ash, gum, hickory, hackberry, beech, and +loblolly pine, thick sapwood is the rule.</p> + +<p>There is no definite relation between the annual rings of growth +and the amount of sapwood. Within the same species the +cross-sectional area of the sapwood is roughly proportional to +the size of the crown of the tree. If the rings are narrow, more +of them are required than where they are wide. As the tree gets +larger, the sapwood must necessarily become thinner or increase +materially in volume. Sapwood is thicker in the upper portion of +the trunk of a tree than near the base, because the age and the +diameter of the upper sections are less.</p> + +<p>When a tree is very young it is covered with limbs almost, if +not entirely, to the ground, but as it grows older some or all +of them will eventually die and be broken off. Subsequent growth +of wood may completely conceal the stubs which, however, will +remain as knots. No matter how smooth and clear a log is on the +outside, it is more or less knotty near the middle. Consequently +the sapwood of an old tree, and particularly of a <a name="pg052"></a> forest-grown +tree, will be freer from knots than the heartwood. Since in most +uses of wood, knots are defects that weaken the timber and +interfere with its ease of working and other properties, it +follows that sapwood, because of its position in the tree, may +have certain advantages over heartwood.</p> + +<p>It is really remarkable that the inner heartwood of old trees +remains as sound as it usually does, since in many cases it is +hundreds of years, and in a few instances thousands of years, +old. Every broken limb or root, or deep wound from fire, +insects, or falling timber, may afford an entrance for decay, +which, once started, may penetrate to all parts of the trunk. +The larvæ of many insects bore into the trees and their tunnels +remain indefinitely as sources of weakness. Whatever advantages, +however, that sapwood may have in this connection are due solely +to its relative age and position.</p> + +<p>If a tree grows all its life in the open and the conditions of +soil and site remain unchanged, it will make its most rapid +growth in youth, and gradually decline. The annual rings of +growth are for many years quite wide, but later they become +narrower and narrower. Since each succeeding ring is laid down +on the outside of the wood previously formed, it follows that +unless a tree materially increases its production of wood from +year to year, the rings must necessarily become thinner. As a +tree reaches maturity its crown becomes more open and the annual +wood production is lessened, thereby reducing still more the +width of the growth rings. In the case of forest-grown trees so +much depends upon the competition of the trees in their struggle +for light and nourishment that periods of rapid and slow growth +may alternate. Some trees, such as southern oaks, maintain the +same width of ring for hundreds of years. Upon the whole, +however, as a tree gets larger in diameter the width of the +growth rings decreases.</p> + +<p>It is evident that there may be decided differences in the grain +of heartwood and sapwood cut from a large tree, particularly one +that is overmature. The relationship between width of growth +rings and the mechanical properties of wood is discussed under +<a href="#II_02">Rate of Growth</a>. In this connection, however, it may be stated +that as a general rule the wood laid on late in the life of a +tree is softer, lighter, weaker, and more even-textured than +that <a name="pg053"></a> produced earlier. It follows that in a large log the +sapwood, because of the time in the life of the tree when it was +grown, may be inferior in hardness, strength, and toughness to +equally sound heartwood from the same log.</p> + +<p>After exhaustive tests on a number of different woods the U.S. +Forest Service concludes as follows: "Sapwood, except that from +old, overmature trees, is as strong as heartwood, other things +being equal, and so far as the mechanical properties go should +not be regarded as a defect."<a name="fn22r"></a><a href="#fn22"><sup><small>22</small></sup></a> Careful inspection of the +individual tests made in the investigation fails to reveal any +relation between the proportion of sapwood and the breaking +strength of timber.</p> + +<p>In the study of the hickories the conclusion was: "There is an +unfounded prejudice against the heartwood. Specifications place +white hickory, or sapwood, in a higher grade than red hickory, +or heartwood, though there is no inherent difference in +strength. In fact, in the case of large and old hickory trees, +the sapwood nearest the bark is comparatively weak, and the best +wood is in the heart, though in young trees of thrifty growth +the best wood is in the sap."<a name="fn23r"></a><a href="#fn23"><sup><small>23</small></sup></a> The results of tests from +selected pieces lying side by side in the same tree, and also +the average values for heartwood and sapwood in shipments of the +commercial hickories without selection, show conclusively that +"the transformation of sapwood into heartwood does not affect +either the strength or toughness of the wood.... It is true, +however, that sapwood is usually more free from latent defects +than heartwood."<a name="fn24r"></a><a href="#fn24"><sup><small>24</small></sup></a></p> + +<p>Specifications for paving blocks often require that longleaf +pine be 90 per cent heart. This is on the belief that sapwood is +not only more subject to decay, but is also weaker than +heartwood. In reality there is no sound basis for discrimination +against sapwood on account of strength, provided other +conditions are equal. It is true that sapwood will not resist +decay as long as heartwood, if both are untreated with +preservatives. It is especially so of woods with deep-colored +heartwood, and is due to infiltrations of tannins, oils, and +resins, which make the wood more or <a name="pg054"></a> less obnoxious to +decay-producing fungi. If, however, the timbers are to be +treated, sapwood is not a defect; in fact, because of the +relative ease with which it can be impregnated with +preservatives it may be made more desirable than heartwood.<a name="fn25r"></a><a href="#fn25"><sup><small>25</small></sup></a></p> + +<p>In specifications for structural timbers reference is sometimes +made to "boxheart," meaning the inclusion of the pith or centre +of the tree within a cross section of the timber. From numerous +experiments it appears that the position of the pith does not +bear any relation to the strength of the material. Since most +season checks, however, are radial, the position of the pith may +influence the resistance of a seasoned beam to horizontal shear, +being greatest when the pith is located in the middle half of +the section.<a name="fn26r"></a><a href="#fn26"><sup><small>26</small></sup></a></p> + +<a name="II_04"></a> +<h3>WEIGHT, DENSITY, AND SPECIFIC GRAVITY</h3> + +<p>From data obtained from a large number of tests on the strength +of different woods it appears that, other things being equal, +the crushing strength parallel to the grain, fibre stress at +elastic limit in bending, and shearing strength along the grain +of wood vary in direct proportion to the weight of dry wood per +unit of volume when green. Other strength values follow +different laws. The hardness varies in a slightly greater ratio +than the square of the density. The work to the breaking point +increases even more rapidly than the cube of density. The +modulus of rupture in bending lies between the first power and +the square of the density. This, of course, is true only in case +the greater weight is due to increase in the amount of wood +substance. A <a name="pg055"></a> wood heavy with resin or other infiltrated +substance is not necessarily stronger than a similar specimen +free from such materials. If differences in weight are due to +degree of seasoning, in other words, to the relative amounts of +water contained, the rules given above will of course not hold, +since strength increases with dryness. But of given specimens of +pine or of oak, for example, in the green condition, the +comparative strength may be inferred from the weight. It is not +permissible, however, to compare such widely different woods as +oak and pine on a basis of their weights.<a name="fn27r"></a><a href="#fn27"><sup><small>27</small></sup></a></p> + +<p>The weight of wood substance, that is, the material which +composes the walls of the fibres and other cells, is practically +the same in all species, whether pine, hickory, or cottonwood, +being a little greater than half again as heavy as water. It +varies slightly from beech sapwood, 1.50, to Douglas fir +heartwood, 1.57, averaging about 1.55 at 30° to 35° C., in terms +of water at its greatest density 4° C. The reason any wood +floats is that the air imprisoned in its cavities buoys it up. +When this is displaced by water the wood becomes water-logged +and sinks. Leaving out of consideration infiltrated substances, +the reason a cubic foot of one kind of dry wood is heavier than +that of another is because it contains a greater amount of wood +substance. <b>Density</b> is merely the weight of a unit of volume, +as 35 pounds per cubic foot, or 0.56 grams per cubic centimetre. +<b>Specific gravity</b> or relative density is the ratio of the +density of any material to the density of distilled water at 4° +C. (39.2° F.). A cubic foot of distilled water at 4° C. weighs +62.43 pounds. Hence the specific gravity of a piece of wood with +a density of 35 pounds is</p> + +<center> +<table summary="text"> +<tbody> +<tr> <td>35<br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td>-------<br></td><td>=<br></td><td>0.561<br></td><td>.<br></td></tr> +<tr> <td>62.43<br></td> <td><br></td> <td><br></td> <td><br></td></tr> +</tbody> +</table> +</center> + +<p>To find the weight +per cubic foot when the specific gravity is given, simply +multiply by 62.43. Thus, 0.561 × 62.43 = 35. In the metric +system, since the weight of a cubic centimetre of pure water is +one gram, the density in grams per cubic centimetre has the same +numerical value as the specific gravity.</p> + +<p>Since the amount of water in wood is extremely variable it +usually is not satisfactory to refer to the density of green +wood. <a name="pg057"></a> For scientific purposes the density of "oven-dry" wood is +used; that is, the wood is dried in an oven at a temperature of +100°C. (212°F.) until a constant weight is attained. For +commercial purposes the weight or density of air-dry or +"shipping-dry" wood is used. This is usually expressed in pounds +per thousand board feet, a board foot being considered as +one-twelfth of a cubic foot.</p> + +<p>Wood shrinks greatly in drying from the green to the oven-dry +condition. (<a href="#TABLE_14">See Table XIV</a>.) Consequently a block of wood +measuring a cubic foot when green will measure considerably less +when oven-dry. It follows that the density of oven-dry wood does +not represent the weight of the dry wood substance in a cubic +foot of green wood. In other words, it is not the weight of a +cubic foot <a name="pg058"></a> of green wood minus the weight of the water which it +contains. Since the latter is often a more convenient figure to +use and much easier to obtain than the weight of oven-dry wood, +it is commonly expressed in tables of "specific gravity or +density of dry wood."</p> + +<a name="pg056"></a> + +<center> +<table id="TABLE_14" summary="TABLE_XIV" border="3" cellspacing="0" cellpadding="1" width="40%"> +<tbody> +<tr><th colspan="7"> TABLE XIV </th></tr> +<tr><th colspan="7"> SPECIFIC GRAVITY, AND SHRINKAGE OF 51 AMERICAN WOODS </th></tr> +<tr><td colspan="7"> (Forest Service Cir. 213) </td></tr> +<tr><th rowspan="3"> COMMON NAME OF SPECIES </th> + <th rowspan="2"> Moisture content </th> + <th colspan="2"> Specific gravity oven-dry, based on </th> + <th colspan="3"> Shrinkage from green to oven-dry condition </th></tr> +<tr> <th> Volume when green </th> + <th> Volume when oven-dry </th> + <th> In volume </th> + <th> Radial </th> + <th> Tangential </th></tr> +<tr> <th> <i>Per cent</i> </th> + <td><br></td> <td><br></td> <th> <i>Per cent</i> </th> + <th> <i>Per cent</i> </th> + <th> <i>Per cent</i> </th></tr> +<tr><th> <i>Hardwoods</i></th> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Ash, black </td> <td> 77 </td> <td> 0.466 </td><td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> white </td> <td> 38 </td> <td> .550 </td> <td> 0.640 </td><td> 12.6 </td><td> 4.3 </td><td> 6.4 </td></tr> +<tr><td> " </td> <td> 47 </td> <td> .516 </td> <td> .590 </td> <td> 11.7 </td><td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Basswood </td> <td> 110 </td><td> .315 </td> <td> .374 </td> <td> 14.5 </td><td> 6.2 </td><td> 8.4 </td></tr> +<tr><td style="text-align: left;"> Beech </td> <td> 61 </td> <td> .556 </td> <td> .669 </td> <td> 16.5 </td><td> 4.6 </td><td> 10.5 </td></tr> +<tr><td style="text-align: left;"> Birch, yellow </td> <td> 72 </td> <td> .545 </td> <td> .661 </td> <td> 17.0 </td><td> 7.9 </td><td> 9.0 </td></tr> +<tr><td style="text-align: left;"> Elm, rock </td> <td> 46 </td> <td> .578 </td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> slippery </td> <td> 57 </td> <td> .541 </td> <td> .639 </td> <td> 15.5 </td><td> 5.1 </td><td> 9.9 </td></tr> +<tr><td style="text-align: left;"> white </td> <td> 66 </td> <td> .430 </td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Gum, red </td> <td> 71 </td> <td> .434 </td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Hackberry </td> <td> 50 </td> <td> .504 </td> <td> .576 </td> <td> 14.0 </td><td> 4.2 </td><td> 8.9 </td></tr> +<tr><td style="text-align: left;"> Hickory, big shellbark </td> <td> 64 </td> <td> .601 </td> <td><br></td> <td> 17.6 </td><td> 7.4 </td><td> 11.2 </td></tr> +<tr><td> " </td> <td> 55 </td> <td> .666 </td> <td><br></td> <td> 20.9 </td><td> 7.9 </td><td> 14.2 </td></tr> +<tr><td style="text-align: left;"> bitternut </td> <td> 65 </td> <td> .624 </td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> mockernut </td> <td> 64 </td> <td> .606 </td> <td><br></td> <td> 16.5 </td><td> 6.9 </td><td> 10.4 </td></tr> +<tr><td> " </td> <td> 57 </td> <td> .662 </td> <td><br></td> <td> 18.9 </td><td> 8.4 </td><td> 11.4 </td></tr> +<tr><td> " </td> <td> 48 </td> <td> .666 </td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> nutmeg </td> <td> 76 </td> <td> .558 </td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> pignut </td> <td> 59 </td> <td> .627 </td> <td><br></td> <td> 15.0 </td><td> 5.6 </td><td> 9.8 </td></tr> +<tr><td> " </td> <td> 54 </td> <td> .667 </td> <td><br></td> <td> 15.3 </td><td> 6.3 </td><td> 9.5 </td></tr> +<tr><td> " </td> <td> 55 </td> <td> .667 </td> <td><br></td> <td> 16.9 </td><td> 6.8 </td><td> 10.9 </td></tr> +<tr><td> " </td> <td> 52 </td> <td> .667 </td> <td><br></td> <td> 21.2 </td><td> 8.5 </td><td> 13.8 </td></tr> +<tr><td style="text-align: left;"> shagbark </td> <td> 65 </td> <td> .608 </td> <td><br></td> <td> 16.0 </td><td> 6.5 </td><td> 10.2 </td></tr> +<tr><td> " </td> <td> 58 </td> <td> .646 </td> <td><br></td> <td> 18.4 </td><td> 7.9 </td><td> 11.4 </td></tr> +<tr><td> " </td> <td> 64 </td> <td> .617 </td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td> " </td> <td> 60 </td> <td> .653 </td> <td><br></td> <td> 15.5 </td><td> 6.5 </td><td> 9.7 </td></tr> +<tr><td style="text-align: left;"> water </td> <td> 74 </td> <td> .630 </td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Locust, honey </td> <td> 53 </td> <td> .695 </td> <td> .759 </td> <td> 8.6 </td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Maple, red </td> <td> 69 </td> <td> .512 </td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> sugar </td> <td> 57 </td> <td> .546 </td> <td> .643 </td> <td> 14.3 </td><td> 4.9 </td><td> 9.1 </td></tr> +<tr><td> " </td> <td> 56 </td> <td> .577 </td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Oak, post </td> <td> 64 </td> <td> .590 </td> <td> .732 </td> <td> 16.0 </td><td> 5.7 </td><td> 10.6 </td></tr> +<tr><td style="text-align: left;"> red </td> <td> 80 </td> <td> .568 </td> <td> .660 </td> <td> 13.1 </td><td> 3.7 </td><td> 8.3 </td></tr> +<tr><td style="text-align: left;"> swamp white </td><td> 74 </td> <td> .637 </td> <td> .792 </td> <td> 17.7 </td><td> 5.5 </td><td> 10.6 </td></tr> +<tr><td style="text-align: left;"> tanbark </td> <td> 88 </td> <td> .585 </td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> white </td> <td> 58 </td> <td> .594 </td> <td> .704 </td> <td> 15.8 </td><td> 6.2 </td><td> 8.3 </td></tr> +<tr><td> " </td> <td> 62 </td> <td> .603 </td> <td> .696 </td> <td> 14.3 </td><td> 4.9 </td><td> 9.0 </td></tr> +<tr><td> " </td> <td> 78 </td> <td> .600 </td> <td> .708 </td> <td> 16.0 </td><td> 4.8 </td><td> 9.2 </td></tr> +<tr><td style="text-align: left;"> yellow </td> <td> 77 </td> <td> .573 </td> <td> .669 </td> <td> 14.2 </td><td> 4.5 </td><td> 9.7 </td></tr> +<tr><td> " </td> <td> 80 </td> <td> .550 </td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Osage orange </td> <td> 31 </td> <td> .761 </td> <td> .838 </td> <td> 8.9 </td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Sycamore </td> <td> 81 </td> <td> .454 </td> <td> .526 </td> <td> 13.5 </td><td> 5.0 </td><td> 7.3 </td></tr> +<tr><td style="text-align: left;"> Tupelo </td> <td> 121 </td><td> .475 </td> <td> .545 </td> <td> 12.4 </td><td> 4.4 </td><td> 7.9 </td></tr> +</tbody> +</table> +</center> + +<center> +<table id="TABLE_14_cont" summary="TABLE_XIV_CONT" border="3" cellspacing="0" cellpadding="1" width="40%"> +<tbody> +<tr><th colspan="7"> TABLE XIV (CONT.) </th></tr> +<tr><th colspan="7"> SPECIFIC GRAVITY, AND SHRINKAGE OF 51 AMERICAN WOODS </th></tr> +<tr><td colspan="7"> (Forest Service Cir. 213) </td></tr> +<tr><th rowspan="3"> COMMON NAME OF SPECIES </th> + <th rowspan="2"> Moisture content </th> + <th colspan="2"> Specific gravity oven-dry, based on </th> + <th colspan="3"> Shrinkage from green to oven-dry condition </th></tr> +<tr> <th> Volume when green </th> + <th> Volume when oven-dry </th> + <th> In volume </th> + <th> Radial </th> + <th> Tangential </th></tr> +<tr> <th> <i>Per cent</i> </th> + <td><br></td> <td><br></td> <th> <i>Per cent</i> </th> + <th> <i>Per cent</i> </th> + <th> <i>Per cent</i> </th></tr> +<tr><th><i> Conifers </i></th> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Arborvitæ</td> <td> 55 </td> <td> .293 </td><td> .315 </td> <td> 7.0 </td> <td> 2.1 </td><td> 4.9 </td></tr> +<tr><td style="text-align: left;"> Cedar, incense</td> <td> 80 </td> <td> .363 </td><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td style="text-align: left;"> Cypress, bald</td> <td> 79 </td> <td> .452 </td><td> .513 </td> <td> 11.5 </td><td> 3.8 </td><td> 6.0 </td></tr> +<tr><td style="text-align: left;"> Fir, alpine</td> <td> 47 </td> <td> .306 </td><td> .321 </td> <td> 9.0 </td> <td> 2.5 </td><td> 7.1 </td></tr> +<tr><td style="text-align: left;"> amabilis</td> <td> 117 </td> <td> .383 </td><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td style="text-align: left;"> Douglas</td> <td> 32 </td> <td> .418 </td><td> .458 </td> <td> 10.9 </td><td> 3.7 </td><td> 6.6 </td></tr> +<tr><td style="text-align: left;"> white</td> <td> 156 </td> <td> .350 </td><td> .437 </td> <td> 10.2 </td><td> 3.4 </td><td> 7.0 </td></tr> +<tr><td style="text-align: left;"> Hemlock (east.)</td> <td> 129 </td> <td> .340 </td><td> .394 </td> <td> 9.2 </td> <td> 2.3 </td><td> 5.0 </td></tr> +<tr><td style="text-align: left;"> Pine, lodgepole</td> <td> 44 </td> <td> .370 </td><td> .415 </td> <td> 11.3 </td><td> 4.2 </td><td> 7.1 </td></tr> +<tr><td style="text-align: left;"> lodgepole</td> <td> 58 </td> <td> .371 </td><td> .407 </td> <td> 10.1 </td><td> 3.6 </td><td> 5.9 </td></tr> +<tr><td style="text-align: left;"> longleaf</td> <td> 63 </td> <td> .528 </td><td> .599 </td> <td> 12.8 </td><td> 6.0 </td><td> 7.6 </td></tr> +<tr><td style="text-align: left;"> red or Nor</td> <td> 54 </td> <td> .440 </td><td> .507 </td> <td> 11.5 </td><td> 4.5 </td><td> 7.2 </td></tr> +<tr><td style="text-align: left;"> shortleaf</td> <td> 52 </td> <td> .447 </td><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td style="text-align: left;"> sugar</td> <td> 123 </td> <td> .360 </td><td> .386 </td> <td> 8.4 </td> <td> 2.9 </td><td> 5.6 </td></tr> +<tr><td style="text-align: left;"> west yellow</td> <td> 98 </td> <td> .353 </td><td> .395 </td> <td> 9.2 </td> <td> 4.1 </td><td> 6.4 </td></tr> +<tr><td> " </td> <td> 125 </td> <td> .377 </td><td> .433 </td> <td> 11.5 </td><td> 4.3 </td><td> 7.3 </td></tr> +<tr><td> " </td> <td> 93 </td> <td> .391 </td><td> .435 </td> <td> 9.9 </td> <td> 3.8 </td><td> 5.8 </td></tr> +<tr><td style="text-align: left;"> white</td> <td> 74 </td> <td> .363 </td><td> .391 </td> <td> 7.8 </td> <td> 2.2 </td><td> 5.9 </td></tr> +<tr><td style="text-align: left;"> Redwood</td><td> 81 </td> <td> .334 </td><td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td> " </td> <td> 69 </td> <td> .366 </td><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td style="text-align: left;"> Spruce, Engelmann </td> <td> 45 </td> <td> .325 </td><td> .359 </td> <td> 10.5 </td><td> 3.7 </td><td> 6.9 </td></tr> +<tr><td> " </td> <td> 156 </td> <td> .299 </td><td> .335 </td> <td> 10.3 </td><td> 3.0 </td><td> 6.2 </td></tr> +<tr><td style="text-align: left;"> red</td> <td> 31 </td> <td> .396 </td><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td style="text-align: left;"> white</td> <td> 41 </td> <td> .318 </td><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td style="text-align: left;"> Tamarack</td><td> 52 </td> <td> .491 </td><td> .558 </td><td> 13.6 </td> <td> 3.7 </td> <td> 7.4 </td></tr> +</tbody> +</table> +</center> + +<p>This weight divided by 62.43 gives the specific gravity per +green volume. It is purely a fictitious quantity. To convert +this figure into actual density or specific gravity of the dry +wood, it is necessary to know the amount of shrinkage in volume. +If <i>S</i> is the percentage of shrinkage from the green to the +oven-dry condition, based on the green volume; <i>D</i>, the density of +the dry wood per cubic foot while green; and <i>d</i> the actual +density of oven-dry wood, then</p> + +<center> +<table summary="text"> +<tbody> +<tr> <td><i>D</i></td> <td><br></td> <td><br></td></tr> +<tr> <td>----------</td> <td>=</td> <td><i>d</i>.</td></tr> +<tr><td><i>1</i> - .0 <i>S</i></td> <td><br></td> <td><br></td></tr> +</tbody> +</table> +</center> + +<p>This relation becomes clearer from the following analysis: +Taking <i>V</i> and <i>W</i> as the volume and weight, respectively, when +green, and <i>v</i> and <i>w</i> as the corresponding volume and weight when +oven-dry, then,</p> + +<! Sorry, the following is just not very conducive to proofreading... /!> + +<center> +<table summary="text"> +<tbody style="text-align: center; vertical-align: middle; white-space: nowrap;"> +<tr><td><br></td><td><br></td><td><i>w</i></td><td style="width: 40px;"><br></td><td><br></td><td><br></td><td><i>W</i></td><td style="width: 40px;"><br></td><td><br></td><td><br></td><td><i>V</i> - <i>v</i></td><td><br></td><td><br></td><td style="width: 40px;"><br></td><td><br></td><td><br></td><td><i>V</i> - <i>v</i></td><td><br></td><td><br></td><td><br></td><td><br></td></tr> +<tr><td><i>d</i></td><td>=</td><td>---</td><td style="width: 40px;"> ; </td><td><i>D</i></td><td>=</td><td>---</td><td style="width: 40px;">;</td><td><i>S</i></td><td>=</td><td>-------</td><td>×</td><td>100</td><td style="width: 40px;">, and</td><td><i>s</i></td><td>= </td><td>-------</td><td>×</td><td>100</td><td>,</td><td><br></td></tr> +<tr><td><br></td><td><br></td><td><i>v</i></td><td style="width: 40px;"><br></td><td><br></td><td><br></td><td><i>V</i></td><td style="width: 40px;"><br></td><td><br></td><td><br></td><td><i>V</i></td><td><br></td><td><br></td><td style="width: 40px;"><br></td><td><br></td><td><br></td><td><i>v</i></td><td><br></td><td><br></td><td><br></td><td><br></td></tr> +</tbody> +</table> +</center> + +<p>in which <i>S</i> is the percentage of shrinkage +from the green to the oven-dry condition, based on the green +volume, and <i>s</i> the same based on the oven-dry volume.</p> + +<p>In tables of specific gravity or density of wood it should +always be stated whether the dry weight per unit of volume when +green or the dry weight per unit of volume when dry is intended, +since the shrinkage in volume may vary from 6 to 50 per cent, +though in conifers it is usually about 10 per cent, and in +hardwoods nearer 15 per cent. (<a href="#TABLE_14">See Table XIV</a>.)</p> + +<a name="II_05"></a> +<h3>COLOR</h3> + +<p>In species which show a distinct difference between heartwood +and sapwood the natural color of heartwood is invariably darker +than that of the sapwood, and very frequently the contrast is +conspicuous. This is produced by deposits in the heartwood of +various materials resulting from the process of growth, +increased possibly by oxidation and other chemical changes, +which usually have little or no appreciable effect on the +mechanical properties of <a name="pg059"></a> the wood. (See <a href="#II_03">Heartwood and Sapwood</a>.) +Some experiments<a name="fn28r"></a><a href="#fn28"><sup><small>28</small></sup></a> on very resinous longleaf pine +specimens, however, indicate an increase in strength. This is +due to the resin which increases the strength when dry. Spruce +impregnated with crude resin and dried is greatly increased in +strength thereby.</p> + +<p>Since the late wood of a growth ring is usually darker in color +than the early wood, this fact may be used in judging the +density, and therefore the hardness and strength of the +material. This is particularly the case with coniferous woods. +In ring-porous woods the vessels of the early wood not +infrequently appear on a finished surface as darker than the +denser late wood, though on cross sections of heartwood the +reverse is commonly true. Except in the manner just stated the +color of wood is no indication of strength.</p> + +<p>Abnormal discoloration of wood often denotes a diseased +condition, indicating unsoundness. The black check in western +hemlock is the result of insect attacks.<a name="fn29r"></a><a href="#fn29"><sup><small>29</small></sup></a> The reddish-brown +streaks so common in hickory and certain other woods are mostly +the result of injury by birds.<a name="fn30r"></a><a href="#fn30"><sup><small>30</small></sup></a> The discoloration is merely +an indication of an injury, and in all probability does not of +itself affect the properties of the wood. Certain rot-producing +fungi impart to wood characteristic colors which thus become +criterions of weakness. Ordinary sap-staining is due to fungous +growth, but does not necessarily produce a weakening effect.<a name="fn31r"></a><a href="#fn31"><sup><small>31</small></sup></a></p> + +<a name="II_06"></a> +<h3>CROSS GRAIN</h3> + +<p><i>Cross grain</i> is a very common defect in timber. One form of it +is produced in lumber by the method of sawing and has no +reference to the natural arrangement of the wood elements. Thus +<a name="pg060"></a> +if the plane of the saw is not approximately parallel to the +axis of the log the grain of the lumber cut is not parallel to +the edges and is termed diagonal. This is likely to occur where +the logs have considerable taper, and in this case may be +produced if sawed parallel to the axis of growth instead of +parallel to the growth rings.</p> + +<p>Lumber and timber with diagonal grain is always weaker than +straight-grained material, the extent of the defect varying with +the degree of the angle the fibres make with the axis of the +stick. In the vicinity of large knots the grain is likely to be +cross. The defect is most serious where wood is subjected to +flexure, as in beams.</p> + +<p><i>Spiral grain</i> is a very common defect in a tree, and when +excessive renders the timber valueless for use except in the +round. It is produced by the arrangement of the wood fibres in a +spiral direction about the axis instead of exactly vertical. +Timber with spiral grain is also known as "torse wood." Spiral +grain usually cannot be detected by casual inspection of a +stick, since it does not show in the so-called visible grain of +the wood, by which is commonly meant a sectional view of the +annual rings of growth cut longitudinally. It is accordingly +very easy to allow spiral-grained material to pass inspection, +thereby introducing an element of weakness in a structure.</p> + +<p>There are methods for readily detecting spiral grain. The +simplest is that of splitting a small piece radially. It is +necessary, of course, that the split be radial, that is, in a +plane passing through the axis of the log, and not tangentially. +In the latter case it is quite probable that the wood would +split straight, the line of cleavage being between the growth +rings.</p> + +<p>In inspection, the elements to examine are the rays. In the case +of oak and certain other hardwoods these rays are so large that +they are readily seen not only on a radial surface, but on the +tangential as well. On the former they appear as flakes, on the +latter as short lines. Since these rays are between the fibres +it naturally follows that they will be vertical or inclined +according as the tree is straight-grained or spiral-grained. +While they are not conspicuous in the softwoods, they can be +seen upon close scrutiny, and particularly so if a small hand +magnifier is used.</p> + +<p>When wood has begun to dry and check it is very easy to see +<a name="pg061"></a> +whether or not it is straight- or spiral-grained, since the +checks will for the most part follow along the rays. If one +examines a row of telephone poles, for example, he will probably +find that most of them have checks running spirally around them. +If boards were sawed from such a pole after it was badly checked +they would fall to pieces of their own weight. The only way to +get straight material would be to split it out.</p> + +<p>It is for this reason that split billets and squares are +stronger than most sawed material. The presence of the spiral +grain has little, if any, effect on the timber when it is used +in the round, but in sawed material the greater the pitch of the +spiral the greater is the defect. + +<a name="II_07"></a> +<h3>KNOTS</h3> + +<p><i>Knots</i> are portions of branches included in the wood of the +stem or larger branch. Branches originate as a rule from the +central axis of a stem, and while living increase in size by the +addition of annual woody layers which are a continuation of +those of the stem. The included portion is irregularly conical +in shape with the tip at the pith. The direction of the fibre is +at right angles or oblique to the grain of the stem, thus +producing local cross grain.</p> + +<p>During the development of a tree most of the limbs, especially +the lower ones, die, but persist for a time—often for years. +Subsequent layers of growth of the stem are no longer intimately +joined with the dead limb, but are laid around it. Hence dead +branches produce knots which are nothing more than pegs in a +hole, and likely to drop out after the tree has been sawed into +lumber. In grading lumber and structural timber, knots are +classified according to their form, size, soundness, and the +firmness with which they are held in place.<a name="fn32r"></a><a href="#fn32"><sup><small>32</small></sup></a></p> + +<p>Knots materially affect checking and warping, ease in working, +and cleavability of timber. They are defects which weaken timber +and depreciate its value for structural purposes where strength +is an important consideration. The weakening effect is much more +<a name="pg062"></a> +serious where timber is subjected to bending and tension than +where under compression. The extent to which knots affect the +strength of a beam depends upon their position, size, number, +direction of fibre, and condition. A knot on the upper side is +compressed, while one on the lower side is subjected to tension. +The knot, especially (as is often the case) if there is a season +check in it, offers little resistance to this tensile stress. +Small, knots, however, may be so located in a beam along the +neutral plane as actually to increase the strength by tending to +prevent longitudinal shearing. Knots in a board or plank are +least injurious when they extend through it at right angles to +its broadest surface. Knots which occur near the ends of a beam +do not weaken it. Sound knots which occur in the central portion +one-fourth the height of the beam from either edge are not +serious defects.</p> + +<p>Extensive experiments by the U.S. Forest Service<a name="fn33r"></a><a href="#fn33"><sup><small>33</small></sup></a> indicate +the following effects of knots on structural timbers:</p> + +<p>(1) Knots do not materially influence the stiffness of +structural timber.</p> + +<p>(2) Only defects of the most serious character affect the +elastic limit of beams. Stiffness and elastic strength are more +dependent upon the quality of the wood fibre than upon defects +in the beam.</p> + +<p>(3) The effect of knots is to reduce the difference between the +fibre stress at elastic limit and the modulus of rupture of +beams. The breaking strength is very susceptible to defects.</p> + +<p>(4) Sound knots do not weaken wood when subject to compression +parallel to the grain.<a name="fn34r"></a><a href="#fn34"><sup><small>34</small></sup></a></p> + +<a name="II_08"></a> +<h3>FROST SPLITS</h3> + +<p>A common defect in standing timber results from radial splits +which extend inward from the periphery of the tree, and almost, +if not always, near the base. It is most common in trees which +split readily, and those with large rays and thin bark. The +<a name="pg063"></a> +primary cause of the splitting is frost, and various theories +have been advanced to explain the action.</p> + +<p>R. Hartig<a name="fn35r"></a><a href="#fn35"><sup><small>35</small></sup></a> believes that freezing forces out a part of the +imbibition water of the cell walls, thereby causing the wood to +shrink, and if the interior layers have not yet been cooled, +tangential strains arise which finally produce radial clefts.</p> + +<p>Another theory holds that the water is not driven out of the +cell walls, but that difference in temperature conditions of +inner and outer layers is itself sufficient to set up the +strains, resulting in splitting. An air temperature of 14°F. or +less is considered necessary to produce frost splits.</p> + +<p>A still more recent theory is that of Busse<a name="fn36r"></a><a href="#fn36"><sup><small>36</small></sup></a> who considers +the mechanical action of the wind a very important factor. He +observed: (<i>a</i>) Frost splits sometimes occur at higher +temperatures than 14°F. (<i>b</i>) Most splits take place shortly +before sunrise, <i>i.e.</i>, at the time of lowest air and soil +temperature; they are never heard to take place at noon, +afternoon, or evening. (<i>c</i>) They always occur between two roots +or between the collars of two roots, (<i>d</i>) They are most +frequent in old, stout-rooted, broad-crowned trees; in younger +stands it is always the stoutest members that are found with +frost splits, while in quite young stands they are altogether +absent, (<i>e</i>) Trees on wet sites are most liable to splits, due +to difference in wood structure, just as difference in wood +structure makes different species vary in this regard. (<i>f</i>) +Frost splits are most numerous less than three feet above the +ground.</p> + +<p>When a tree is swayed by the wind the roots are counteracting +forces, and the wood fibres are tested in tension and +compression by the opposing forces; where the roots exercise +tension stresses most effectively the effect of compression +stresses is at a minimum; only where the pressure is in excess +of the tension, <i>i.e.</i>, between the roots, can a separation of +the fibre result. Hence, when by frost a tension on the entire +periphery is established, and the <a name="pg064"></a> wind localizes additional +strains, failure occurs. The stronger the compression and +tension, the severer the strains and the oftener failures occur. +The occurrence of reports of frost splits on wind-still days is +believed by Busse to be due to the opening of old frost splits +where the tension produced by the frost alone is sufficient.</p> + +<p>Frost splits may heal over temporarily, but usually open up +again during the following winter. The presence of old splits is +often indicated by a ridge of callous, the result of the +cambium's effort to occlude the wound. Frost splits not only +affect the value of lumber, but also afford an entrance into the +living tree for disease and decay.</p> + +<a name="II_09"></a> +<h3>SHAKES, GALLS, PITCH POCKETS</h3> + +<p><i>Heart shake</i> occurs in nearly all overmature timber, being more +frequent in hardwoods (especially oak) than in conifers. In +typical heart shake the centre of the hole shows indications of +becoming hollow and radial clefts of varying size extend outward +from the pith, being widest inward. It frequently affects only +the butt log, but may extend to the entire hole and even the +larger branches. It usually results from a shrinkage of the +heartwood due probably to chemical changes in the wood.</p> + +<p>When it consists of a single cleft extending across the pith it +is termed <i>simple heart shake</i>. Shake of this character in +straight-grained trees affects only one or two central boards +when cut into lumber, but in spiral-grained timber the damage is +much greater. When shake consists of several radial clefts it is +termed <i>star shake</i>. In some instances one or more of these +clefts may extend nearly to the bark. In felled or converted +timber clefts due to heart shake may be distinguished from +seasoning cracks by the darker color of the exposed surfaces. +Such clefts, however, tend to open up more and more as the +timber seasons.</p> + +<p><i>Cup</i> or <i>ring shake</i> results from the pulling apart of two or +more growth rings. It is one of the most serious defects to +which sound timber is subject, as it seriously reduces the +technical properties of wood. It is very common in sycamore and +in western larch, particularly in the butt portion. Its +occurrence is most frequent at the junction of two growth layers +of very unequal <a name="pg065"></a> thickness. Consequently it is likely to occur in +trees which have grown slowly for a time, then abruptly +increased, due to improved conditions of light and food, as in +thinning. Old timber is more subject to it than young trees. The +damage is largely confined to the butt log. Cup shake is often +associated with other forms of shake, and not infrequently shows +traces of decay.</p> + +<p>The causes of cup shake are uncertain. The swaying action of the +wind may result in shearing apart the growth layers, especially +in trees growing in exposed places. Frost may in some instances +be responsible for cup shake or at least a contributing factor, +although trees growing in regions free from frost often have +ring shake. Shrinkage of the heartwood may be concentric as well +as radial in its action, thus producing cup shake instead of, or +in connection with, heart shake.</p> + +<p>A local defect somewhat similar in effect to cup shake is known +as <i>rind gall</i>. If the cambium layer is exposed by the removal +of the entire bark or rind it will die. Subsequent growth over +the damaged portion does not cohere with the wood previously +formed by the old cambium. The defect resulting is termed rind +gall. The most common causes of it are fire, gnawing, blazing, +chipping, sun scald, lightning, and abrasions.</p> + +<p><i>Heart break</i> is a term applied to areas of compression failure +along the grain found in occasional logs. Sometimes these breaks +are invisible until the wood is manufactured into the finished +article. The occurrence of this defect is mostly limited to the +dense hardwoods, such as hickory and to heavy tropical species. +It is the source of considerable loss in the fancy veneer +industry, as the veneer from valuable logs so affected drops to +pieces.</p> + +<p>The cause of heart break is not positively known. It is highly +probable, however, that when the tree is felled the trunk +strikes across a rock or another log, and the impact causes +actual failure in the log as in a beam.</p> + +<p><i>Resin</i> or <i>pitch pockets</i> are of common occurrence in the wood +of larch, spruce, fir, and especially of longleaf and other hard +pines. They are due to accumulations of resin in openings +between adjacent layers of growth. They are more frequent in +trees growing alone than in those of dense stands. The pockets +are usually a few inches in greatest dimension and affect only +one or <a name="pg066"></a> two growth layers. They are hidden until exposed by the +saw, rendering it impossible to cut lumber with reference to +their position. Often several boards are damaged by a single +pocket. In grading lumber, pitch pockets are classified as +small, standard, and large, depending upon their width and +length.</p> + +<a name="II_10"></a> +<h3>INSECT INJURIES<a name="fn37r"></a><a href="#fn37"><sup><small>37</small></sup></a></h3> + +<p>The larvæ of many insects are destructive to wood. Some attack +the wood of living trees, others only that of felled or +converted material. Every hole breaks the continuity of the +fibres and impairs the strength, and if there are very many of +them the material may be ruined for all purposes where strength +is required.</p> + +<p>Some of the most common insects attacking the wood of living +trees are the oak timber worm, the chestnut timber worm, +carpenter worms, ambrosia beetles, the locust borer, turpentine +beetles and turpentine borers, and the white pine weevil.</p> + +<p>The insect injuries to forest products may be classed according +to the stage of manufacture of the material. Thus round timber +with the bark on, such as poles, posts, mine props, and sawlogs, +is subject to serious damage by the same class of insects as +those mentioned above, particularly by the round-headed borers, +timber worms, and ambrosia beetles. Manufactured unseasoned +products are subject to damage from ambrosia beetles and other +wood borers. Seasoned hardwood lumber of all kinds, rough +handles, wagon stock, etc., made partially or entirely of +sapwood, are often reduced in value from 10 to 90 per cent by a +class of insects known as powder-post beetles. Finished hardwood +products such as handles, wagon, carriage and machinery stock, +especially if ash or hickory, are often destroyed by the +powder-post beetles. Construction timbers in buildings, bridges +and trestles, cross-ties, poles, mine props, fence posts, etc., +are sometimes seriously injured by wood-boring larvæ, termites, +black ants, carpenter bees, and powder-post beetles, and +sometimes reduced <a name="pg067"></a> in value from 10 to 100 per cent. In tropical +countries termites are a very serious pest in this respect.</p> + +<a name="II_11"></a> +<h3>MARINE WOOD-BORER INJURIES</h3> + +<p>Vast amounts of timber used for piles in wharves and other +marine structures are constantly being destroyed or seriously +injured by marine borers. Almost invariably they are confined to +salt water, and all the woods commonly used for piling are +subject to their attacks. There are two genera of mollusks, +<i>Xylotrya</i> and <i>Teredo</i>, and three of crustaceans, <i>Limnoria, +Chelura</i>, and <i>Sphoeroma</i>, that do serious damage in many places +along both the Atlantic and Pacific coasts.</p> + +<p>These mollusks, which are popularly known as "shipworms," are +much alike in structure and mode of life. They attack the +exposed surface of the wood and immediately begin to bore. The +tunnels, often as large as a lead pencil, extend usually in a +longitudinal direction and follow a very irregular, tangled +course. Hard woods are apparently penetrated as readily as soft +woods, though in the same timber the softer parts are preferred. +The food consists of infusoria and is not obtained from the wood +substance. The sole object of boring into the wood is to obtain +shelter.</p> + +<p>Although shipworms can live in cold water they thrive best and +are most destructive in warm water. The length of time required +to destroy an average barked, unprotected pine pile on the +Atlantic coast south from Chesapeake Bay and along the entire +Pacific coast varies from but one to three years.</p> + +<p>Of the crustacean borers, <i>Limnoria</i>, or the "wood louse," is +the only one of great importance, although <i>Sphoeroma</i> is +reported destructive in places. <i>Limnoria</i> is about the size of +a grain of rice and tunnels into the wood for both food and +shelter. The galleries extend inward radially, side by side, in +countless numbers, to the depth of about one-half inch. The thin +wood partitions remaining are destroyed by wave action, so that +a fresh surface is exposed to attack. Both hard and soft woods +are damaged, but the rate is faster in the soft woods or softer +portions of a wood.</p> + +<p>Timbers seriously attacked by marine borers are badly <a name="pg068"></a> weakened +or completely destroyed. If the original strength of the +material is to be preserved it is necessary to protect the wood +from the borers. This is sometimes accomplished by proper +injection of creosote oil, and more or less successfully by the +use of various kinds of external coatings.<a name="fn38r"></a><a href="#fn38"><sup><small>38</small></sup></a> No treatment, +however, has proved entirely satisfactory.</p> + +<a name="II_12"></a> +<h3>FUNGOUS INJURIES<a name="fn39r"></a><a href="#fn39"><sup><small>39</small></sup></a></h3> + +<p>Fungi are responsible for almost all decay of wood. So far as +known, all decay is produced by living organisms, either fungi +or bacteria. Some species attack living trees, sometimes killing +them, or making them hollow, or in the case of pecky cypress and +incense cedar filling the wood with galleries like those of +boring insects. A much larger variety work only in felled or +dead wood, even after it is placed in buildings or manufactured +articles. In any case the process of destruction is the same. +The mycelial threads penetrate the walls of the cells in search +of food, which they find either in the cell contents (starches, +sugars, etc.), or in the cell wall itself. The breaking down of +the cell walls through the chemical action of so-called +"enzymes" secreted by the fungi follows, and the eventual +product is a rotten, moist substance crumbling readily under the +slightest pressure. Some species remove the ligneous matter and +leave almost pure cellulose, which is white, like cotton; others +dissolve the cellulose, leaving a brittle, dark brown mass of +ligno-cellulose. Fungi (such as the bluing fungus) which merely +stain wood usually do not affect its mechanical properties +unless the attacks are excessive.</p> + +<p>It is evident, then, that the action of rot-causing fungi is to +decrease the strength of wood, rendering it unsound, brittle, +and <a name="pg069"></a> dangerous to use. The most dangerous kinds are the so-called +"dry-rot" fungi which work in many kinds of lumber after it is +placed in the buildings. They are particularly to be dreaded +because unseen, working as they do within the walls or inside of +casings. Several serious wrecks of large buildings have been +attributed to this cause. It is stated<a name="fn40r"></a><a href="#fn40"><sup><small>40</small></sup></a> that in the three +years (1911-1913) more than $100,000 was required to repair +damage due to dry rot.</p> + +<p>Dry rot develops best at 75°F. and is said to be killed by a +temperature of 110°F.<a name="fn41r"></a><a href="#fn41"><sup><small>41</small></sup></a> Fully 70 per cent humidity is +necessary in the air in which a timber is surrounded for the +growth of this fungus, and probably the wood must be quite near +its fibre saturation condition. Nevertheless <i>Merulius +lacrymans</i> (one of the most important species) has been found to +live four years and eight months in a dry condition.<a name="fn42r"></a><a href="#fn42"><sup><small>42</small></sup></a> +Thorough kiln-drying will kill this fungus, but will not prevent +its redevelopment. Antiseptic treatment, such as creosoting, is +the best prevention.</p> + +<p>All fungi require moisture and air<a name="fn43r"></a><a href="#fn43"><sup><small>43</small></sup></a> for their growth. +Deprived of either of these the fungus dies or ceases to +develop. Just what degree of moisture in wood is necessary for +the "dry-rot" fungus has not been determined, but it is +evidently considerably above that of thoroughly air-dry timber, +probably more than 15 per cent moisture. Hence the importance of +free circulation of air about all timbers in a building.</p> + +<p>Warmth is also conducive to the growth of fungi, the most +favorable temperature being about 90°F. They cannot grow in +extreme cold, although no degree of cold such as occurs +naturally will kill them. On the other hand, high temperature +will kill them, but the spores may survive even the boiling +temperature. Mould fungus has been observed to develop rapidly +at 130°F. in a dry kiln in moist air, a condition under which an +animal cannot <a name="pg070"></a> live more than a few minutes. This fungus was +killed, however, at about 140° or 145°F.<a name="fn44r"></a><a href="#fn44"><sup><small>44</small></sup></a></p> + +<p>The fungus (<i>Endothia parasitica</i> And.) which causes the +chestnut blight kills the trees by girdling them and has no +direct effect upon the wood save possibly the four or five +growth rings of the sapwood.<a name="fn45r"></a><a href="#fn45"><sup><small>45</small></sup></a></p> + +<a name="II_13"></a> +<h3>PARASITIC PLANT INJURIES.<a name="fn46r"></a><a href="#fn46"><sup><small>46</small></sup></a></h3> + +<p>The most common of the higher parasitic plants damaging timber +trees are mistletoes. Many species of deciduous trees are +attacked by the common mistletoe (<i>Phoradendron flavescens</i>). It +is very prevalent in the South and Southwest and when present in +sufficient quantity does considerable damage. There is also a +considerable number of smaller mistletoes belonging to the genus +<i>Razoumofskya (Arceuthobium)</i> which are widely distributed +throughout the country, and several of them are common on +coniferous trees in the Rocky Mountains and along the Pacific +coast.</p> + +<p>One effect of the common mistletoe is the formation of large +swellings or tumors. Often the entire tree may become stunted or +distorted. The western mistletoe is most common on the branches, +where it produces "witches' broom." It frequently attacks the +trunk as well, and boards cut from such trees are filled with +long, radial holes which seriously damage or destroy the value +of the timber affected.</p> + +<a name="II_14"></a> +v<h3>LOCALITY OF GROWTH</h3> + +<p>The data available regarding the effect of the locality of +growth upon the properties of wood are not sufficient to warrant +<a name="pg071"></a> +definite conclusions. The subject has, however, been kept in +mind in many of the U.S. Forest Service timber tests and the +following quotations are assembled from various reports:</p> + +<p>"In both the Cuban and longleaf pine the locality where grown +appears to have but little influence on weight or strength, and +there is no reason to believe that the longleaf pine from one +State is better than that from any other, since such variations +as are claimed can be found on any 40-acre lot of timber in any +State. But with loblolly and still more with shortleaf this +seems not to be the case. Being widely distributed over many +localities different in soil and climate, the growth of the +shortleaf pine seems materially influenced by location. The wood +from the southern coast and gulf region and even Arkansas is +generally heavier than the wood from localities farther north. +Very light and fine-grained wood is seldom met near the southern +limit of the range, while it is almost the rule in Missouri, +where forms resembling the Norway pine are by no means rare. The +loblolly, occupying both wet and dry soils, varies accordingly." +Cir. No. 12, p. 6.</p> + +<p>" ... It is clear that as all localities have their heavy and +their light timber, so they all share in strong and weak, hard +and soft material, and the difference in quality of material is +evidently far more a matter of individual variation than of soil +or climate." <i>Ibid.</i>, p.22</p> + +<p>"A representative committee of the Carriage Builders' +Association had publicly declared that this important industry +could not depend upon the supplies of southern timber, as the +oak grown in the South lacked the necessary qualities demanded +in carriage construction. Without experiment this statement +could be little better than a guess, and was doubly unwarranted, +since it condemned an enormous amount of material, and one +produced under a great variety of conditions and by at least a +dozen species of trees, involving, therefore, a complexity of +problems difficult enough for the careful investigator, and +entirely beyond the few unsystematic observations of the members +of a committee on a flying trip through one of the greatest +timber regions of the world.</p> + +<p>"A number of samples were at once collected (part of them +supplied by the carriage builders' committee), and the fallacy +of the broad statement mentioned was fully demonstrated by a +short <a name="pg072"></a> series of tests and a more extensive study into structure +and weight of these materials. From these tests it appears that +pieces of white oak from Arkansas excelled well-selected pieces +from Connecticut, both in stiffness and endwise compression (the +two most important forms of resistance)." Report upon the +forestry investigations of the U.S.D.A. 1877-1898, p. 331. See +also Rep. of Div. of For., 1890, p. 209.</p> + +<p>"In some regions there are many small, stunted hickories, which +most users will not touch. They have narrow sap, are likely to +be birdpecked, and show very slow growth. Yet five of these +trees from a steep, dry south slope in West Virginia had an +average strength fully equal to that of the pignut from the +better situation, and were superior in toughness, the work to +maximum load being 36.8 as against 31.2 for pignut. The trees +had about twice as many rings per inch as others from better +situations.</p> + +<p>"This, however, is not very significant, as trees of the same +species, age, and size, growing side by side under the same +conditions of soil and situation, show great variation in their +technical value. It is hard to account for this difference, but +it seems that trees growing in wet or moist situations are +rather inferior to those growing on fresher soil; also, it is +claimed by many hickory users that the wood from limestone soils +is superior to that from sandy soils.</p> + +<p>"One of the moot questions among hickory men is the relative +value of northern and southern hickory. The impression prevails +that southern hickory is more porous and brash than hickory from +the north. The tests ... indicate that southern hickory is as +tough and strong as northern hickory of the same age. But the +southern hickories have a greater tendency to be shaky, and this +results in much waste. In trees from southern river bottoms the +loss through shakes and grub-holes in many cases amounts to as +much as 50 per cent.</p> + +<p>"It is clear, therefore, that the difference in northern and +southern hickory is not due to geographic location, but rather +to the character of timber that is being cut. Nearly all of that +from southern river bottoms and from the Cumberland Mountains is +from large, old-growth trees; that from the north is from +younger trees which are grown under more favorable conditions, +and it is <a name="pg073"></a> due simply to the greater age of the southern trees +that hickory from that region is lighter and more brash than +that from the north." Bul. 80, pp. 52-55.</p> + +<a name="II_15"></a> +<h3>SEASON OF CUTTING</h3> + +<p>It is generally believed that winter-felled timber has decided +advantages over that cut at other seasons of the year, and to +that cause alone are frequently ascribed much greater +durability, less liability to check and split, better color, and +even increased strength and toughness. The conclusion from the +various experiments made on the subject is that while the time +of felling may, and often does, affect the properties of wood, +such result is due to the weather conditions rather than to the +condition of the wood.</p> + +<p>There are two phases of this question. One is concerned with the +physiological changes which might take place during the year in +the wood of a living tree. The other deals with the purely +physical results due to the weather, as differences in +temperature, humidity, moisture, and other features to be +mentioned later.</p> + +<p>Those who adhere to the first view maintain that wood cut in +summer is quite different in composition from that cut in +winter. One opinion is that in summer the "sap is up," while in +winter it is "down," consequently winter-felled timber is drier. +A variation of this belief is that in summer the sap contains +certain chemicals which affect the properties of wood and does +not contain them in winter. Again it is sometimes asserted that +wood is actually denser in winter than in summer, as part of the +wood substance is dissolved out in the spring and used for plant +food, being restored in the fall.</p> + +<p>It is obvious that such views could apply only to sapwood, since +it alone is in living condition at the time of cutting. +Heartwood is dead wood and has almost no function in the +existence of the tree other than the purely mechanical one of +support. Heartwood does undergo changes, but they are gradual +and almost entirely independent of the seasons.</p> + +<p>Sapwood might reasonably be expected to respond to seasonal +changes, and to some extent it does. Just beneath the bark there +is a thin layer of cells which during the growing season have +not <a name="pg074"></a> attained their greatest density. With the exception of this +one annual ring, or portion of one, the density of the wood +substance of the sapwood is nearly the same the year round. +Slight variations may occur due to impregnation with sugar and +starch in the winter and its dissolution in the growing season. +The time of cutting can have no material effect on the inherent +strength and other mechanical properties of wood except in the +outermost annual ring of growth.</p> + +<p>The popular belief that sap is up in the spring and summer and +is down in the winter has not been substantiated by experiment. +There are seasonal differences in the composition of sap, but so +far as the amount of sap in a tree is concerned there is fully +as much, if not more, during the winter than in summer. +Winter-cut wood is not drier, to begin with, than +summer-felled—in reality, it is likely to be wetter.<a name="fn47r"></a><a href="#fn47"><sup><small>47</small></sup></a></p> + +<p>The important consideration in regard to this question is the +series of circumstances attending the handling of the timber +after it is felled. Wood dries more rapidly in summer than in +winter, not because there is less moisture at one time than +another, but because of the higher temperature in summer. This +greater heat is often accompanied by low humidity, and +conditions are favorable for the rapid removal of moisture from +the exposed portions of wood. Wood dries by evaporation, and +other things being equal, this will proceed much faster in hot +weather than in cold.</p> + +<p>It is a matter of common observation that when wood dries it +shrinks, and if shrinkage is not uniform in all directions the +material pulls apart, causing season checks. (<a href="#fig27">See Fig. 27</a>.) If +evaporation proceeds more rapidly on the outside than inside, +the greater shrinkage of the outer portions is bound to result +in many checks, the number and size increasing with the degree +of inequality of drying.</p> + +<p>In cold weather, drying proceeds slowly but uniformly, thus +allowing the wood elements to adjust themselves with the least +amount of rupturing. In summer, drying proceeds rapidly and +<a name="pg075"></a> +irregularly, so that material seasoned at that time is more +likely to split and check.</p> + +<p>There is less danger of sap rot when trees are felled in winter +because the fungus does not grow in the very cold weather, and +the lumber has a chance to season to below the danger point +before the fungus gets a chance to attack it. If the logs in +each case could be cut into lumber immediately after felling and +given exactly the same treatment, for example, kiln-dried, no +difference due to the season of cutting would be noted.</p> + +<a name="II_16"></a> +<h3>WATER CONTENT<a name="fn48r"></a><a href="#fn48"><sup><small>48</small></sup></a></h3> + +<p>Water occurs in living wood in three conditions, namely: (1) in +the cell walls, (2) in the protoplasmic contents of the cells, +and (3) as free water in the cell cavities and spaces. In +heartwood it occurs only in the first and last forms. Wood that +is thoroughly air-dried retains from 8 to 16 per cent of water +in the cell walls, and none, or practically none, in the other +forms. Even oven-dried wood retains a small percentage of +moisture, but for all except chemical purposes, may be +considered absolutely dry.</p> + +<p>The general effect of the water content upon the wood substance +is to render it softer and more pliable. A similar effect of +common observation is in the softening action of water on +rawhide, paper, or cloth. Within certain limits the greater the +water content the greater its softening effect.</p> + +<p>Drying produces a decided increase in the strength of wood, +particularly in small specimens. An extreme example is the case +of a completely dry spruce block two inches in section, which +will sustain a permanent load four times as great as that which +a green block of the same size will support.</p> + +<p>The greatest increase due to drying is in the ultimate crushing +strength, and strength at elastic limit in endwise compression; +these are followed by the modulus of rupture, and stress at +elastic limit in cross-bending, while the modulus of elasticity +is least affected. These ratios are shown in Table XV, but it is +to be noted <a name="pg076"></a> that they apply only to wood in a much drier +condition than is used in practice. For air-dry wood the ratios +are considerably lower, particularly in the case of the ultimate +strength and the elastic limit. Stiffness (within the elastic +limit), while following a similar law, is less affected. In the +case of shear parallel to the grain, the general effect of +drying is to increase the strength, but this is often offset by +small splits and checks caused by shrinkage.</p> + +<center> +<table id="TABLE_15" summary="TABLE_XV" border="3" cellspacing="0" cellpadding="1" width="80%"> +<tbody> +<tr><th colspan="7"> TABLE XV </th></tr> +<tr><th colspan="7"> EFFECT OF DRYING ON THE MECHANICAL PROPERTIES OF WOOD, +SHOWN IN RATIO OF INCREASE DUE TO REDUCING MOISTURE CONTENT FROM THE GREEN +CONDITION TO KILN-DRY (3.5 PER CENT) </th></tr> +<tr><td colspan="7"> (Forest Service Bul. 70, p. 89) </td></tr> +<tr><th rowspan="2"> KIND OF STRENGTH </th> <th colspan="2"> Longleaf pine </th> <th colspan="2"> Spruce </th> <th colspan="2"> Chestnut </th></tr> +<tr> <th> (1) </th> <th> (2) </th> <th> (1) </th> <th> (2) </th> <th> (1) </th> <th> (2) </th></tr> +<tr><td style="text-align: left;"> Crushing strength parallel to grain </td> <td> 2.89 </td><td> 2.60 </td> <td> 3.71 </td> <td> 3.41 </td> <td> 2.83 </td><td> 2.55 </td></tr> +<tr><td style="text-align: left;"> Elastic limit in compression parallel to grain </td> <td> 2.60 </td><td> 2.34 </td> <td> 3.80 </td> <td> 3.49 </td> <td> 2.40 </td><td> 2.26 </td></tr> +<tr><td style="text-align: left;"> Modulus of rupture in bending </td> <td> 2.50 </td><td> 2.20 </td> <td> 2.81 </td> <td> 2.50 </td> <td> 2.09 </td><td> 1.82 </td></tr> +<tr><td style="text-align: left;"> Stress at elastic limit in bending </td> <td> 2.90 </td><td> 2.55 </td> <td> 2.90 </td> <td> 2.58 </td> <td> 2.30 </td><td> 2.00 </td></tr> +<tr><td style="text-align: left;"> Crushing strength at right angles to grain </td> <td><br></td> <td><br></td> <td> 2.58 </td> <td> 2.48 </td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Shearing strength parallel to grain </td> <td>2.01 </td> <td> 1.91 </td> <td> 2.03 </td> <td> 1.95 </td> <td> 1.55 </td><td> 1.47 </td></tr> +<tr><td style="text-align: left;"> Modulus of elasticity in compression parallel to grain </td><td>1.63 </td> <td> 1.47 </td> <td> 2.26 </td> <td> 2.08 </td> <td> 1.43 </td><td> 1.29 </td></tr> +<tr><td style="text-align: left;"> Modulus of elasticity in bending </td> <td>1.59 </td> <td> 1.35 </td> <td> 1.43 </td> <td> 1.23 </td> <td> 1.44 </td><td> 1.21 </td></tr> +<tr><td style="text-align: left;" colspan="7"> NOTE.—The figures in the first +column show the relative increase in strength between a green specimen +and a kiln-dry specimen of equal size. The figures in the second column +show the relative increase of strength of the same block after being +dried from a green condition to 3.5 per cent moisture, correction +having been made for shrinkage. That is, in the first column the +strength values per actual unit of area are used; in the second +the values per unit of area of green wood which shrinks to smaller size +when dried. See also Cir. 108, Fig. 1, p. 8. </td></tr> +</tbody> +</table> +</center> + +<p>The moisture content has a decided bearing also upon the manner +in which wood fails. In compression tests on very dry <a name="pg077"></a> specimens +the entire piece splits suddenly into pieces before any buckling +takes place (<a href="#fig09">see Fig. 9</a>.), while with wet material the block +gives way gradually, due to the buckling or bending of the walls +of the fibres along one or more shearing planes. (<a href="#fig14">See Fig. 14</a>.) +In bending tests on wet beams, first failure occurs by +compression on top of the beam, gradually extending downward +toward the neutral axis. Finally the beam ruptures at <a name="pg078"></a> the +bottom. In the case of very dry beams the failure is usually by +splitting or tension on the under side (<a href="#fig17">see Fig. 17</a>.), without +compression on the upper, and is often sudden and without +warning, and even while the load is still increasing. The effect +varies somewhat with different species, chestnut, for example, +becoming more brittle upon drying than do ash, hemlock, and +longleaf pine. The tensile strength of wood is least affected by +drying, as a rule.</p> + +<p>In drying wood no increase in strength results until the free +water is evaporated and the cell walls begin to dry<a name="fn49r"></a><a href="#fn49"><sup><small>49</small></sup></a>. This +critical point has been called the <i>fibre-saturation point</i>. +(<a href="#fig24">See Fig. 24</a>.) Conversely, after the cell walls are saturated +with water, any increase in the amount of water absorbed merely +fills the cavities and intercellular spaces, and has no effect +on the mechanical properties. Hence, soaking green wood does not +lessen its strength unless the water is heated, whereupon a +decided weakening results.</p> + +<p class="ctr"><img src="images/fig24.jpg" alt="Figure 24" id="fig24" /></p> +<p class="imgtitle">Figure 24</p> +<p class="imgtext"> Relation of the moisture content to the +various strength values of spruce. FSP = fibre-saturation +point.</p> + +<p>The strengthening effects of drying, while very marked in the +case of small pieces, may be fully offset in structural timbers +by inherent weakening effects due to the splitting apart of the +wood elements as a result of irregular shrinkage, and in some +cases also to the slitting of the cell walls (<a href="#fig25">see Fig. 25</a>). +Consequently with large timbers in commercial use it is unsafe +to count upon any greater strength, even after seasoning, than +that of the green or fresh condition.</p> + +<p class="ctr"><img src="images/fig25.jpg" alt="Figure 25" id="fig25" /></p> +<p class="imgtitle">Figure 25</p> +<p class="imgtext"> Cross section of the wood of western +larch showing fissures in the thick-walled cells of the late +wood. Highly magnified. <i>Photo by U. S. Forest Service.</i></p> + +<p>In green wood the cells are all intimately joined together and +are at their natural or normal size when saturated with water. +The cell walls may be considered as made up of little particles +with water between them. When wood is dried the films of water +between the particles become thinner and thinner until almost +entirely gone. As a result the cell walls grow thinner with loss +of moisture,—in other words, the cell shrinks.</p> + +<p>It is at once evident that if drying does not take place +uniformly throughout an entire piece of timber, the shrinkage as +a <a name="pg080"></a> whole cannot be uniform. The process of drying is from the +outside inward, and if the loss of moisture at the surface is +met by a steady capillary current of water from the inside, the +shrinkage, so far as the degree of moisture affected it, would +be uniform. In the best type of dry kilns this condition is +approximated by first heating the wood thoroughly in a moist +atmosphere before allowing drying to begin.</p> + +<p>In air-seasoning and in ordinary dry kilns this condition too +often is not attained, and the result is that a dry shell is +formed which encloses a moist interior. (<a href="#fig26">See Fig. 26</a>.) +Subsequent drying out of the inner portion is rendered more +difficult by this "case-hardened" condition. As the outer part +dries it is prevented from shrinking by the wet interior, which +is still at its greatest volume. This outer portion must either +check open or the fibres become strained in tension. If this +outer shell dries while the fibres are thus strained they become +"set" in this condition, and are no longer in tension. Later +when the inner part dries, it tends to shrink away from the +hardened outer shell, so that the inner fibres are now strained +in tension and the outer fibres are in compression. If the +stress exceeds the cohesion, numerous cracks open up, producing +a "honey-combed" condition, or "hollow-horning," as it is +called. If such a case-hardened stick of wood be resawed, the +two halves will cup from the internal tension and external +compression, with the concave surface inward.</p> + +<p class="ctr"><img src="images/fig26.jpg" alt="Figure 26" id="fig26" /></p> +<p class="imgtitle">Figure 26</p> +<p class="imgtext"> Progress of drying throughout the +length of a chestnut beam, the black spots indicating the +presence of free water in the wood. The first section at the +left was cut one-fourth inch from the end, the next one-half +inch, the next one inch, and all the others one inch apart. The +illustration shows case-hardening very clearly. <i>Photo by U. S. +Forest Service.</i></p> + +<p>For a given surface area the loss of water from wood is always +greater from the ends than from the sides, due to the fact that +the vessels and other water-carriers are cut across, allowing +ready entrance of drying air and outlet for the water vapor. +Water does not flow out of boards and timbers of its own accord, +but must be evaporated, though it may be forced out of very +sappy specimens by heat. In drying a log or pole with the bark +on, most of the water must be evaporated through the ends, but +in the case of peeled timbers and sawn boards the loss is +greatest from the surface because the area exposed is so much +greater.</p> + +<p>The more rapid drying of the ends causes local shrinkage, and +were the material sufficiently plastic the ends would become +bluntly tapering. The rigidity of the wood substance prevents +this and the fibres are split apart. Later, as the remainder of +the <a name="pg081"></a> stick dries many of the checks will come together, though +some of the largest will remain and even increase in size as the +drying proceeds. (<a href="#fig27">See Fig. 27</a>.)</p> + +<p class="ctr"><img src="images/fig27.jpg" alt="Figure 27" id="fig27" /></p> +<p class="imgtitle">Figure 27</p> +<p class="imgtext"> Excessive season checking. <i>Photo by U.S. +Forest Service.</i></p> + +<p>A wood cell shrinks very little lengthwise. A dry wood cell is, +therefore, practically of the same length as it was in a green +or saturated condition, but is smaller in cross section, has +thinner walls, and a larger cavity. It is at once evident that +this fact makes shrinkage more irregular, for wherever cells +cross each other at a decided angle they will tend to pull apart +upon drying. This occurs wherever pith rays and wood fibres +meet. A considerable portion of every wood is made up of these +rays, which for the most part have their cells lying in a radial +direction instead of longitudinally. (<a href="#fig00">See Frontispiece</a>.) In +pine, over 15,000 of these occur on a square inch of a +tangential section, and even in oak the very large rays which +are readily visible to the eye as flakes <a name="pg082"></a> on quarter-sawed +material represent scarcely one per cent of the number which the +microscope reveals.</p> + +<p>A pith ray shrinks in height and width, that is, vertically and +tangentially as applied to the position in a standing tree, but +very little in length or radially. The other elements of the +wood shrink radially and tangentially, but almost none +lengthwise or vertically as applied to the tree. Here, then, we +find the shrinkage of the rays tending to shorten a stick of +wood, while the other cells resist it, and the tendency of a +stick to get smaller in circumference is resisted by the endwise +reaction or thrust of the rays. Only in a tangential direction, +or around the stick in direction of the annual rings of growth, +do the two forces coincide. Another factor to the same end is +that the denser bands of late wood are continuous in a +tangential direction, while radially they are separated by +alternate zones of less dense early wood. Consequently the +shrinkage along the rings (tangential) is fully twice as much as +toward the centre (radial). (<a href="#TABLE_14">See Table XIV</a>.) This explains why +some cracks open more and more as drying advances. (<a href="#fig27">See Fig. +27</a>.)</p> + +<p>Although actual shrinkage in length is small, nevertheless the +tendency of the rays to shorten a stick produces strains which +are responsible for some of the splitting open of ties, posts, +and sawed timbers with box heart. At the very centre of a tree +the wood is light and weak, while farther out it becomes denser +and stronger. Longitudinal shrinkage is accordingly least at the +centre and greater toward the outside, tending to become +greatest in the sapwood. When a round or a box-heart timber +dries fast it splits radially, and as drying continues the cleft +widens partly on account of the greater tangential shrinkage and +also because the greater contraction of the outer fibres warps +the sections apart. If a small hardwood stem is split while +green for a short distance at the end and placed where it can +dry out rapidly, the sections will become bow-shaped with the +concave sides out. These various facts, taken together, explain +why, for example, an oak tie, pole, or log may split open its +entire length if drying proceeds rapidly and far enough. Initial +stresses in the living trees produce a similar effect when the +log is sawn into boards. This is especially so in <i>Eucalyptus +globulus</i> and to a less extent with any rapidly grown wood.</p> + +<a name="pg083"></a> + +<p>The use of S-shaped thin steel clamps to prevent large checks +and splits is now a common practice in this country with +crossties and poles as it has been for a long time in European +countries. These devices are driven into the butts of the +timbers so as to cross incipient checks and prevent their +widening. In place of the regular S-hook another of crimped iron +has been devised. (<a href="#fig28">See Fig. 28</a>.) Thin straps of iron with one +tapered edge are run between intermeshing cogs and crimped, +after which they may be cut off any length desired. The time for +driving S-irons of either form is when the cracks first appear.</p> + +<p class="ctr"><img src="images/fig28.jpg" alt="Figure 28" id="fig28" /></p> +<p class="imgtitle">Figure 28</p> +<p class="imgtext"> Control of season checking by the use +of S-irons. <i>Photo by U. S. Forest Service.</i></p> + +<p>The tendency of logs to split emphasizes the importance of +converting them into planks or timbers while in a green +condition. Otherwise the presence of large checks may render +much lumber worthless which might have been cut out in good +condition. The loss would not be so great if logs were perfectly +straight-grained, but this is seldom the case, most trees +growing more or less spirally or irregularly. Large pieces crack +more than smaller ones, quartered lumber less than that sawed +through and through, thin pieces, especially veneers, less than +thicker boards.</p> + +<p>In order to prevent cracks at the ends of boards, small straps +of wood may be nailed on them or they may be painted. This +<a name="pg084"></a> +method is usually considered too expensive, except in the case +of valuable material. Squares used for shuttles, furniture, +gun-stocks, and tool handles should always be protected at the +ends. One of the best means is to dip them into melted +paraffine, which seals the ends and prevents loss of moisture +there. Another method is to glue paper on the ends. In some +cases abroad paper is glued on to all the surfaces of valuable +exotic balks. Other substances sometimes employed for the +purpose of sealing the wood are grease, carbolineum, wax, clay, +petroleum, linseed oil, tar, and soluble glass. In place of +solid beams, built-up material is often preferable, as the +disastrous results of season checks are thereby largely overcome +or minimized.</p> + +<a name="II_17"></a> +<h3>TEMPERATURE</h3> + +<p>The effect of temperature on wood depends very largely upon the +moisture content of the wood and the surrounding medium. If +absolutely dry wood is heated in absolutely dry air the wood +expands. The extent of this expansion is denoted by a +coefficient corresponding to the increase in length or other +dimensions for each degree rise in temperature divided by the +original length or other dimension of the specimen. The +coefficient of linear expansion of oak has been found to be +.00000492; radial expansion, .0000544, or about eleven times the +longitudinal. Spruce expands less than oak, the ratio of radial +to longitudinal expansion being about six to one. Metals and +glass expand equally in all directions, since they are +homogeneous substances, while wood is a complicated structure. +The coefficient of expansion of iron is .0000285, or nearly six +times the coefficient of linear expansion of oak and seven times +that of spruce<a name="fn50r"></a><a href="#fn50"><sup><small>50</small></sup></a>.</p> + +<p>Under ordinary conditions wood contains more or less moisture, +so that the application of heat has a drying effect which is +accompanied by shrinkage. This shrinkage completely obscures the +expansion due to the heating.</p> + +<p>Experiments made at the Yale Forest School revealed the effect +of temperature on the crushing strength of wet wood. In the case +<a name="pg085"></a> +of wet chestnut wood the strength decreases 0.42 per cent for +each degree the water is heated above 60° F.; in the case of +spruce the decrease is 0.32 per cent.</p> + +<p>The effects of high temperature on wet wood are very marked. +Boiling produces a condition of great pliability, especially in +the case of hardwoods. If wood in this condition is bent and +allowed to dry, it rigidly retains the shape of the bend, though +its strength may be somewhat reduced. Except in the case of very +dry wood <a name="pg086"></a> the effect of cold is to increase the strength and +stiffness of wood. The freezing of any free water in the pores +of the wood will augment these conditions.</p> + +<p>The effect of steaming upon the strength of cross-ties was +investigated by the U.S. Forest Service in 1904. The conclusions +were summarized as follows:</p> + +<p>"(1) The steam at pressure up to 40 pounds applied for 4 hours, +or at a pressure of 20 pounds up to 20 hours, increases the +weight of ties. At 40 pounds' pressure applied for 4 hours and +at 20 pounds for 5 hours the wood began to be scorched.</p> + +<p>"(2) The steamed and saturated wood, when tested immediately +after treatment, exhibited weaknesses in proportion to the +pressure and duration of steaming. (<a href="#TABLE_16">See Table XVI</a>.) If allowed +to air-dry subsequently the specimens regained the greater part +of their strength, provided the pressure and duration had not +exceeded those cited under (1). Subsequent immersion in water of +the steamed wood and dried specimens showed that they were +weaker than natural wood similarly dried and resoaked."<a name="fn51r"></a><a href="#fn51"><sup><small>51</small></sup></a></p> + +<center> +<table id="TABLE_16" summary="TABLE_XVI" border="3" cellspacing="0" cellpadding="1" width="100%"> +<tbody> +<tr><th colspan="8"> TABLE XVI </th></tr> +<tr><th colspan="8"> EFFECT OF STEAMING ON THE STRENGTH OF GREEN LOBLOLLY PINE </th></tr> +<tr><td colspan="8"> (Forest Service, Cir. 39) </td></tr> +<tr><th rowspan="5"> Treatment </th> <th colspan="3"> Cylinder conditions </th> <th colspan="4"> Strength</th></tr> +<tr> <th colspan="3"> Steaming </th><th colspan="2"> Static </th><th> Impact </th><th><br></th></tr><tr><th>Period </th><th> Pressure </th><th> Temperature </th><th> Bending modulus of rupture </th><th> Compression parallel to grain </th><th> Height of drop causing complete failure </th><th> Average of the three strengths </th></tr> +<tr> <th rowspan="2"><i>Hrs.</i></th> + <th rowspan="2"><i>Lbs. per sq. inch</i></th> + <th rowspan="2"> °<i>F.</i></th> + <th> <i>Per cent</i> </th> + <th> <i>Per cent</i> </th> + <th> <i>Per cent</i> </th> + <th> <i>Per cent</i> </th></tr> +<tr> <th colspan="4"> Untreated wood = 100% </th></tr> +<tr><th rowspan="7"> Steam, at pressures various </th> <td> 4 </td> <td><br></td> <td> 230[a] </td><td> 91.3 </td> <td> 79.1 </td><td> 96.4 </td> <td> 88.9 </td></tr> +<tr> <td> 4 </td> <td> 10 </td> <td> 238 </td> <td> 78.2 </td> <td> 93.7 </td><td> 93.3 </td> <td> 88.4 </td></tr> +<tr> <td> 4 </td> <td> 20 </td> <td> 253 </td> <td> 83.3 </td> <td> 84.2 </td><td> 91.4 </td> <td> 80.8 </td></tr> +<tr> <td> 4 </td> <td> 30 </td> <td> 269 </td> <td> 80.4 </td> <td> 78.4 </td><td> 89.8 </td> <td> 82.9 </td></tr> +<tr> <td> 4 </td> <td> 40 </td> <td> 283 </td> <td> 78.1 </td> <td> 74.4 </td><td> 74.0 </td> <td> 75.5 </td></tr> +<tr> <td> 4 </td> <td> 50 </td> <td> 292 </td> <td> 75.8 </td> <td> 71.5 </td><td> 63.9 </td> <td> 70.4 </td></tr> +<tr> <td> 4 </td> <td> 100 </td><td> 337 </td> <td> 41.4 </td> <td> 65.0 </td><td> 55.2 </td> <td> 53.9 </td></tr> +<tr><th rowspan="8" colspan="1"> Steam, for various periods </th><td> 1 </td> <td> 20 </td> <td> 257 </td> <td> 100.6 </td><td> 98.6 </td><td> 86.7 </td> <td> 95.3 </td></tr> +<tr> <td> 2 </td> <td> 20 </td> <td> 267 </td> <td> 88.4 </td> <td> 93.0 </td><td> 107.0 </td><td> 96.1 </td></tr> +<tr> <td> 3 </td> <td> 20 </td> <td> 260 </td> <td> 90.0 </td> <td> 93.6 </td><td> 84.1 </td> <td> 89.2 </td></tr> +<tr> <td> 4 </td> <td> 20 </td> <td> 253 </td> <td> 83.3 </td> <td> 84.2 </td><td> 91.4 </td> <td> 86.3 </td></tr> +<tr> <td> 5 </td> <td> 20 </td> <td> 253 </td> <td> 85.0 </td> <td> 78.1 </td><td> 84.2 </td> <td> 82.4 </td></tr> +<tr> <td> 6 </td> <td> 20 </td> <td> 242 </td> <td> 95.2 </td> <td> 89.8 </td><td> 76.0 </td> <td> 87.0 </td></tr> +<tr> <td> 10 </td><td> 20 </td> <td> 255 </td> <td> 73.7 </td> <td> 82.0 </td><td> 76.0 </td> <td> 77.2 </td></tr> +<tr> <td> 20 </td><td> 20 </td> <td> 258 </td> <td> 67.5 </td> <td> 65.0 </td><td> 99.0 </td> <td> 77.2 </td></tr> +<tr><td style="text-align: left" rowspan="1" colspan="8"> [Footnote a: It will be noted that +the temperature was 230°. This is the maximum temperature by the +maximum-temperature recording thermometer, and is due to the +handling of the exhaust valve. The average temperature was that +of exhaust +steam.] </td></tr> +</tbody> +</table> +</center> + +<p>"(3) A high degree of steaming is injurious to wood in strength +and spike-holding power. The degree of steaming at which +pronounced harm results will depend upon the quality of the wood +and its degree of seasoning, and upon the pressure (temperature) +of steam and the duration of its application. For loblolly pine +the limit of safety is certainly 30 pounds for 4 hours, or 20 +pounds for 6 hours."<a name="fn52r"></a><a href="#fn52"><sup><small>52</small></sup></a></p> + +<p>Experiments made at the Yale Forest School showed that steaming +above 30 pounds' gauge pressure reduces the strength of wood +permanently while wet from 25 to 75 per cent.</p> + +<a name="II_18"></a> +<h3>PRESERVATIVES</h3> + +<p>The exact effects of chemical impregnation upon the mechanical +properties of wood have not been fully determined, though they +have been the subject of considerable investigation.<a name="fn53r"></a><a href="#fn53"><sup><small>53</small></sup></a> More +<a name="pg087"></a> +depends upon the method of treatment than upon the preservatives +used. Thus preliminary steaming at too high pressure or for too +long a period will materially weaken the wood, (<a href="#II_17">See Tempurature, +<i>supra</i></a>.)</p> + +<p>The presence of zinc chloride does not weaken wood under static +loading, although the indications are that the wood becomes +brittle under impact. If the solution is too strong it will +decompose the wood.</p> + +<p>Soaking in creosote oil causes wood to swell, and accordingly +decreases the strength to some extent, but not nearly so much so +as soaking in water.<a name="fn54r"></a><a href="#fn54"><sup><small>54</small></sup></a></p> + +<p>Soaking in kerosene seems to have no significant weakening +effect.<a name="fn55r"></a><a href="#fn55"><sup><small>55</small></sup></a></p> + +<a name="pg088"></a> +<a name="PART_III"></a> +<h2>PART III<br>TIMBER TESTING<a name="fn56r"></a><a href="#fn56"><sup><small>56</small></sup></a></h2> + +<a name="III_01"></a> +<h3>WORKING PLAN</h3> + +<p>Preliminary to making a series of timber tests it is very +important that a working plan be prepared as a guide to the +investigation. This should embrace: (1) the purpose of the +tests; (2) kind, size, condition, and amount of material needed; +(3) full description of the system of marking the pieces; (4) +details of any special apparatus and methods employed; (5) +proposed method of analyzing the data obtained and the nature of +the final report. Great care should be taken in the preparation +of this plan in order that all problems arising may be +anticipated so far as possible and delays and unnecessary work +avoided. A comprehensive study of previous investigations along +the same or related lines should prove very helpful in outlining +the work and preparing the report. (For sample working plan <a href="#APPENDIX">see +Appendix</a>.)</p> + +<a name="III_02"></a> +<h3>FORMS OF MATERIAL TESTED</h3> + +<p>In general, four forms of material are tested, namely: (1) large +timbers, such as bridge stringers, car sills, large beams, and +other pieces five feet or more in length, of actual sizes and +grades in common use; (2) built-up structural forms and +fastenings, such as built-up beams, trusses, and various kind of +joints; (3) small clear pieces, such as are used in compression, +shear, cleavage, and small cross-breaking tests; (4) +manufactured articles, such as axles, spokes, shafts, +wagon-tongues, cross-arms, insulator pins, barrels, and packing +boxes.</p> + +<p>As the moisture content is of fundamental importance (<a href="#II_16">see Water Content</a>, +pages 75-84.), all standard tests are usually <a name="pg089"></a> made in the +green condition. Another series is also usually run in an +air-dry condition of about 12 per cent moisture. In all cases +the moisture is very carefully determined and stated with the +results in the tables.</p> + +<a name="III_03"></a> +<h3>SIZE OF TEST SPECIMENS</h3> + +<p>The size of the test specimen must be governed largely by the +purpose for which the test is made. If the effect of a single +factor, such as moisture, is the object of experiment, it is +necessary to use small pieces of wood in order to eliminate so +far as possible all disturbing factors. If the specimens are too +large, it is impossible to secure enough perfect pieces from one +tree to form a series for various tests. Moreover, the drying +process with large timbers is very difficult and irregular, and +requires a long period of time, besides causing checks and +internal stresses which may obscure the results obtained.</p> + +<p>On the other hand, the smaller the dimensions of the test +specimen the greater becomes the relative effect of the inherent +factors affecting the mechanical properties. For example, the +effect of a knot of given size is more serious in a small stick +than in a large one. Moreover, the smaller the specimen the +fewer growth rings it contains, hence there is greater +opportunity for variation due to irregularities of grain.</p> + +<p>Tests on large timbers are considered necessary to furnish +designers data on the probable strength of the different sizes +and grades of timber on the market; their coefficients of +elasticity under bending (since the stiffness rather than the +strength often determines the size of a beam); and the manner of +failure, whether in bending fibre stress or horizontal shear. It +is believed that this information can only be obtained by direct +tests on the different grades of car sills, stringers, and other +material in common use.</p> + +<p>When small pieces are selected for test they very often are +clear and straight-grained, and thus of so much better grade +than the large sticks that tests upon them may not yield unit +values applicable to the larger sizes. Extensive experiments +show, however, (1) that the modulus of elasticity is +approximately the <a name="pg090"></a> same for large timbers as for small clear +specimens cut from them, and (2) that the fibre stress at +elastic limit for large beams is, except in the weakest timbers, +practically equal to the crushing strength of small clear pieces +of the same material.<a name="fn57r"></a><a href="#fn57"><sup><small>57</small></sup></a></p> + +<a name="III_04"></a> +<h3>MOISTURE DETERMINATION</h3> + +<p>In order for tests to be comparable, it is necessary to know the +moisture content of the specimens at the zone of failure. This +is determined from disks an inch thick cut from the timber +immediately after testing.</p> + +<p>In cases, as in large beams, where it is desirable to know not +only the average moisture content but also its distribution +through the timber, the disks are cut up so as to obtain an +outside, a middle, and an inner portion, of approximately equal +areas. Thus in a section 10" × 12" the outer strip would be one +inch wide, and the second one a little more than an inch and a +quarter. Moisture determinations are made for each of the three +portions separately.</p> + +<p>The procedure is as follows:</p> + +<p>(1) Immediately after sawing, loose splinters are removed and +each section is weighed.</p> + +<p>(2) The material is put into a drying oven at 100° C. (212° F.) +and dried until the variation in weight for a period of +twenty-four hours is less than 0.5 per cent.</p> + +<p>(3) The disk is again carefully weighed.</p> + +<p>(4) The loss in weight expressed in per cent of the dry weight +indicates the moisture content of the specimen from which the +specimen was cut.</p> + +<a name="III_05"></a> +<h3>MACHINE FOR STATIC TESTS</h3> + +<p>The standard screw machines used for metal tests are also used +for wood, but in the case of wood tests the readings must be +taken "on the fly," and the machine operated at a uniform speed +without interruption from beginning to end of the test. This is +on account of the time factor in the strength of wood. (See +Speed of Testing Machine, <a href="#pg092">page 92</a>.)</p> + +<a name="pg091"></a> + +<p>The standard machines for static tests can be used for +transverse bending, compression, tension, shear, and cleavage. A +common form consists of three main parts, namely: (1) the +straining mechanism, (2) the weighing apparatus, and (3) the +machinery for communicating motion to the screws.</p> + +<p>The straining mechanism consists of two parts, one of which is a +movable crosshead operated by four (sometimes two or three) +upright steel straining screws which pass through openings in +the platform and bear upward on the bed of the machine upon +which the weighing platform rests as a fulcrum. At the lower +ends of these screws are geared nuts all rotated simultaneously +by a system of gears which cause the movable crosshead to rise +and fall as desired.</p> + +<p>The stationary part of the straining mechanism, which is used +only for tension and cleavage tests, consists of a steel cage +above the movable crosshead and rests directly upon the weighing +platform. The top of the cage contains a square hole into which +one end of the test specimen may be clamped, the crosshead +containing a similar clamp for the other end, in making tension +tests.</p> + +<p>For testing long beams a special form of machine with an +extended platform is used. (<a href="#fig29">See Fig. 29</a>.)</p> + +<p>The weighing platform rests upon knife edges carried by primary +levers of the weighing apparatus, the fulcrum being on the bed +of the machine, and any pressure upon it is directly transmitted +through a series of levers to the weighing beam. This beam is +adjusted by means of a poise running on a screw. In operation +the beam is kept floating by means of another poise moved back +and forth by a screw which is operated by a hand wheel or +automatically. The larger units of stress are read from the +graduations along the side of the beam, while the intermediate +smaller weights are observed on the dial on the rear end of the +beam.</p> + +<p>The machine is driven by power from a shaft or a motor and is so +geared that various speeds are obtainable. One man can operate +it.</p> + +<p>In making tests the operation of the straining screws is always +downward so as to bring pressure to bear upon the weighing +platform. For tests in tension and cleavage the specimen is +placed <a name="pg092"></a> between the top of the stationary cage and the movable +head and subjected to a pull. For tests in transverse bending, +compression, and cleavage the specimen is placed between the +movable head and the platform, and a direct compression force +applied.</p> + +<p>Testing machines are usually calibrated to a portion of their +capacity before leaving the factory. The delicacy of the +weighing levers is verified by determining the number of pounds +necessary to move the beam between the stops while a load of +1,000 pounds rests on the platform. The usual requirement is +that ten pounds should accomplish this movement.</p> + +<p>The size of machine suitable for compression tests on 2" × 2" +sticks or for 2" × 2" beams with 26 to 36-inch span has a +capacity of 30,000 pounds.</p> + +<a name="III_06"></a> +<h3>SPEED OF TESTING MACHINE</h3> + +<p>In instructions for making static tests the rate of application +of the stress, <i>i.e.</i>, the speed of the machine, is given +because the strength of wood varies with the speed at which the +fibres are strained. The speed of the crosshead of the testing +machine is practically never constant, due to mechanical defects +of the apparatus and variations in the speed of the motor, but +so long as it does not exceed 25 per cent the results will not +be appreciably affected. In fact, a change in speed of 50 per +cent will not cause the strength of the wood to vary more than 2 +per cent.<a name="fn58r"></a><a href="#fn58"><sup><small>58</small></sup></a></p> + +<p>Following are the formulæ used in determining the speed of the +movable head of the machine in inches per minute (n):</p> + +<center> +<table summary="text"> +<tbody> +<tr><td>(1)</td> <td style="text-align: left;"> For endwise compression </td> <td>n</td> <td>=</td> <td>Z l</td></tr> +<tr><td><br></td><td><br></td> <td><br></td><td><br></td><td>Z l<sup>2</sup></td></tr> +<tr><td>(2)</td> <td style="text-align: left;"> For beams (centre loading) </td> <td>n</td> <td>=</td> <td>------</td></tr> +<tr><td><br></td><td><br></td> <td><br></td><td><br></td><td>6h</td></tr> +<tr><td><br></td><td><br></td> <td><br></td><td><br></td><td> Z l<sup>2</sup></td></tr> +<tr><td>(3)</td> <td style="text-align: left;"> For beams (third-point loading) </td><td>n</td> <td>=</td> <td>------</td></tr> +<tr><td><br></td><td><br></td> <td><br></td><td><br></td><td>5.4 h</td></tr> +<tr><td><br></td><td><br></td> <td><br></td><td><br></td><td><br></td></tr> +<tr><td><br></td><td><br></td> <td>Z</td> <td>=</td> <td style="text-align: left;"> rate of fibre strain per inch of fibre length.</td></tr> +<tr><td><br></td><td><br></td> <td>l</td> <td>=</td> <td style="text-align: left;"> span of beam or length of compression specimen.</td></tr> +<tr><td><br></td><td><br></td> <td>h</td> <td>=</td> <td style="text-align: left;"> height of beam.</td></tr> +</tbody> +</table> +</center> + +<a name="pg094"></a> + +<center> +<table summary="text"> +<tbody> +<tr><td colspan="4"> The values commonly used for Z are as follows:</td></tr> +<tr><td style="text-align: left;"> Bending large beams </td> <td> Z </td><td> = </td><td> 0.0007 </td></tr> +<tr><td style="text-align: left;"> Bending small beams </td> <td> Z </td><td> = </td><td> 0.0015 </td></tr> +<tr><td style="text-align: left;"> Endwise compression-large specimens </td> <td> Z </td><td> = </td><td> 0.0015 </td></tr> +<tr><td style="text-align: left;"> Endwise compression-small specimens </td> <td> Z </td><td> = </td><td> 0.003 </td></tr> +<tr><td style="text-align: left;"> Right-angled compression-large specimens </td><td> Z </td><td> =</td> <td> 0.007 </td></tr> +<tr><td style="text-align: left;"> Right-angled compression-small specimens </td><td> Z </td><td> = </td><td> 0.015 </td></tr> +<tr><td style="text-align: left;"> Shearing parallel to the grain </td> <td> Z </td><td> = </td><td> 0.015 </td></tr> +</tbody> +</table> +</center> + +<p>Example: At what speed should the crosshead move to give the +required rate of fibre strain in testing a small beam 2" × 2" × +30". (Span = 28".) Substituting these values in equation (2) +above:</p> + +<center> +<table summary="text"> +<tbody> +<tr><td><br></td><td><br></td><td> (0.0015 × 28<sup><small>2</small></sup>) </td><td><br></td><td><br></td></tr> +<tr><td>n</td> <td> = </td> <td> ----------------- </td> <td> = </td><td> 0.1 inch per minute. </td></tr> +<tr><td><br></td><td><br></td><td> (6 × 2)</td> <td><br></td><td><br></td></tr> +</tbody> +</table> +</center> + +<p>In order that tests may be intelligently compared, it is +important that account be taken of the speed at which the stress +was applied. In determining the basis for a ratio between time +and strength the rate of strain, which is controllable, and not +the ratio of stress, which is circumstantial, should be used. In +other words, the rate at which the movable head of the testing +machine descends and not the rate of increase in the load is to +be regulated. This ratio, to which the name <i>speed-strength +modulus</i> has been given, may be expressed as a coefficient +which, if multiplied into any proportional change in speed, will +give the proportional change in strength. This ratio is derived +from empirical curves. (<a href="#TABLE_17">See Table XVII</a>.)</p> + +<a name="pg093"></a> + +<center> +<table id="TABLE_17" summary="TABLE_XVII" border="3" cellspacing="0" cellpadding="1" width="100%"> +<tbody> +<tr><th colspan="23"> TABLE XVII </th></tr> +<tr><th colspan="23"> SPEED-STRENGTH MODULI AND RELATIVE INCREASE IN STRENGTH AT RATES OF FIBRE STRAIN INCREASING IN GEOMETRICAL RATIO. (Tiemann, <i>loc. cit.</i>) </th></tr> +<tr><td rowspan="1" colspan="23"> (Values in parentheses are approximate) </td></tr> +<tr><th colspan="2"> Rate of fibre strain.<br>Ten-thousandths inch per minute per inch </th> <th colspan="3"> 2/3 </th> <th colspan="3"> 2 </th> <th colspan="3"> 6 </th> <th colspan="3"> 18 </th> <th colspan="3"> 54 </th> <th colspan="3"> 162 </th> <th colspan="3"> 486 </th></tr> +<tr><th rowspan="4" colspan="1"> COMPRESSION </th><th> Speed of crosshead.<br>Inches per minute</th><th colspan="3"> 0.000383 </th> <th colspan="3"> 0.00115 </th> <th colspan="3"> 0.00345 </th> <th colspan="3"> 0.0103</th> <th colspan="3"> 0.0310</th> <th colspan="3"> 0.0931</th> <th colspan="3"> .279</th></tr> +<tr> <th> Specimens </th> <th> Wet </th> <th> Dry </th> <th> All </th> <th> Wet </th> <th> Dry </th> <th> All </th> <th> Wet </th> <th> Dry </th> <th> All </th> <th> Wet </th> <th> Dry </th> <th> All </th> <th> Wet </th> <th> Dry </th> <th> All </th> <th> Wet </th> <th> Dry </th> <th> All </th> <th> Wet </th> <th> Dry </th> <th> All </th></tr> +<tr> <th> Relative crushing strength</th> <td><br></td> <td><br></td> <td><br></td> <td> 100.0 </td><td> 100.0 </td><td> 100.0 </td><td> 103.4 </td><td> 100.8 </td><td> 101.5 </td><td> 107.5 </td><td> 102.7 </td><td> 103.8 </td><td> 113.9 </td><td> 105.5 </td><td> 107.9 </td><td> 121.3 </td><td> 108.3 </td><td> 116.4 </td><td> 128.8 </td><td> 110.0 </td><td> 118.9 </td></tr> +<tr> <th> Speed-strength modulus, <i>T</i><br></th> <td><br></td> <td><br></td> <td><br></td> <td> 0.017 </td><td>(0.006)</td><td>(0.009)</td><td> 0.033 </td><td> 0.012 </td><td> 0.016 </td><td> 0.047 </td><td> 0.021 </td><td> 0.029 </td><td> 0.053 </td><td> 0.027 </td><td> 0.039 </td><td> 0.060 </td><td> 0.023 </td><td> 0.049 </td><td>(0.052)</td><td>(0.015)</td><td>(0.040)</td></tr> +<tr><th rowspan="4"> BENDING </th> <th> Speed of crosshead.<br>Inches per minute </th> <th colspan="3"> 0.0072 </th> <th colspan="3"> 0.0216 </th> <th colspan="3"> 0.0648 </th> <th colspan="3"> 0.194 </th> <th colspan="3"> 0.583 </th> <th colspan="3"> 1.75 </th> <th colspan="3"> 5.25 </th></tr> +<tr> <th> Specimens </th> <th> Wet </th> <th> Dry </th> <th> All </th> <th> Wet </th> <th> Dry </th> <th> All </th> <th> Wet </th> <th> Dry </th> <th> All </th> <th> Wet </th> <th> Dry </th> <th> All </th> <th> Wet </th> <th> Dry </th> <th> All </th> <th> Wet </th> <th> Dry </th> <th> All </th> <th> Wet </th> <th> Dry </th> <th> All </th></tr> +<tr> <th> Relative crushing strength </th> <td> 97.4 </td> <td> 99.0 </td> <td> 98.2 </td> <td> 100.0 </td><td> 100.0 </td><td> 100.0 </td><td> 105.1 </td><td> 102.1 </td><td> 103.7 </td><td> 111.3 </td><td> 105.8 </td><td> 108.1 </td><td> 117.9 </td><td> 108.6 </td><td> 112.7 </td><td> 123.7 </td><td> 109.6 </td><td> 116.3 </td><td> 126.3 </td><td> 110.3 </td><td> 118.9 </td></tr> +<tr> <th> Speed-strength modulus, <i>T</i><br></th> <td>(0.014)</td><td>(0.005)</td><td> 0.012 </td><td> 0.033 </td><td> 0.014 </td><td> 0.026 </td><td> 0.049 </td><td> 0.026 </td><td> 0.037 </td><td> 0.053 </td><td> 0.033 </td><td> 0.038 </td><td> 0.049 </td><td> 0.014 </td><td> 0.035 </td><td> 0.038 </td><td> 0.006 </td><td> 0.025 </td><td>(0.023)</td><td>(0.004)</td><td>(0.014)</td></tr> +<tr align="left"><td rowspan="1" colspan="23"> NOTE.—The usual speeds of testing at the U.S. Forest Service laboratory are at rates of fibre strain of 15 and 10 ten-thousandths in. per min. per in. for compression and bending respectively. </td></tr> +</tbody> +</table> +</center> + +<a name="III_07"></a> +<h3>BENDING LARGE BEAMS</h3> + +<p><i>Apparatus</i>: A static bending machine (described above), with a +special crosshead for third-point loading and a long platform +bearing knife-edge supports, is required. (<a href="#fig29">See Fig. 29</a>.)</p> + +<p class="ctr"><img src="images/fig29.jpg" alt="Figure 29" id="fig29" /></p> +<p class="imgtitle">Figure 29</p> +<p class="imgtext"> Static bending test on large beam. Note +arrangement of wire and scale for measuring deflection; also +method of applying load at "third-points."</p> + +<p><i>Preparing the material</i>: Standard sizes and grades of beams and +timbers in common use are employed. The ends are roughly squared +and the specimen weighed and measured, taking the +cross-sectional dimensions midway of the length. Weights should +be to the nearest pound, lengths to the nearest 0.1 inch, and +cross-sectional dimensions to the nearest 0.01 inch.</p> + +<p><i>Marking and sketching</i>: The butt end of the beam is marked <a name="pg095"></a> <i>A</i> +and the top end <i>B</i>. While facing <i>A</i>, the top side is marked +<i>a</i>, the right hand <i>b</i>, the bottom <i>c</i>, the left hand <i>d</i>. +Sketches are made of each side and end, showing (1) size, +location, and condition of knots, checks, splits, and other +defects; (2) irregularities of grain; (3) distribution of +heartwood and sapwood; and on the ends: (4) the location of the +pith and the arrangement of the growth rings, (5) number of +rings per inch, and (6) the proportion of late wood.</p> + +<p>The number of rings per inch and the proportion of late wood +should always be determined along a radius or a line normal to +the rings. The average number of rings per inch is the total +number of rings divided by the length of the line crossing them. +The proportion of late wood is equal to the sum of the widths of +the late wood crossed by the line, divided by the length of the +line. Rings per inch should be to the nearest 0.1; late wood to +the nearest 0.1 per cent.</p> + +<p>Since in large beams a great variation in rate of growth and +<a name="pg096"></a> +relative amount of late wood is likely in different parts of the +section, it is advisable to consider the cross section in three +volumes, namely, the upper and lower quarters and the middle +half. The determination should be made upon each volume +separately, and the average for the entire cross section +obtained from these results.</p> + +<p>At the conclusion of the test the failure, as it appears on each +surface, is traced on the sketches, with the failures numbered +in the order of their occurrence. If the beam is subsequently +cut up and used for other tests an additional sketch may be +desirable to show the location of each piece.</p> + +<p><i>Adjusting specimen in machine</i>: The beam is placed in the +machine with the side marked <i>a</i> on top, and with the ends +projecting equally beyond the supports. In order to prevent +crushing of the fibre at the points where the stress is applied +it is necessary to use bearing blocks of maple or other hard +wood with a convex surface in contact with the beam. Roller +bearings should be placed between the bearing blocks and the +knife edges of the crosshead to allow for the shortening due to +flexure. (<a href="#fig29">See Fig. 29</a>.) Third-point loading is used, that is, +the load is applied at two points one-third the span of the beam +apart. (<a href="#fig30">See Fig. 30</a>.) This affords a uniform bending moment +throughout the central third of the beam.</p> + +<p class="ctr"><img src="images/fig30.jpg" alt="Figure 30" id="fig30" /></p> +<p class="imgtitle">Figure 30</p> +<p class="imgtext"> Two methods of loading a beam, namely, +third-point loading (upper), and centre loading (lower).</p> + +<p><i>Measuring the deflection</i>: The method of measuring the +deflection should be such that any compression at the points of +support or at the application of the load will not affect the +reading. This may be accomplished by driving a small nail near +each end of the beam, the exact location being on the neutral +plane and vertically above each knife-edge support. Between +these nails a fine wire is stretched free of the beam and kept +taut by means of a rubber band or coiled spring on one end. +Behind the wire at a point on the beam midway between the +supports a steel scale graduated to hundredths of an inch is +fastened vertically by means of thumb-tacks or small screws +passing through holes in it. Attachment should be made on the +neutral plane.</p> + +<p>The first reading is made when the scale beam is balanced at +zero load, and afterward at regular increments of the load which +is applied continuously and at a uniform speed. (See +Speed of <a name="pg097"></a> Testing Machine, <a href="#pg092">page 92</a>.) +If desired, however, the load may be +read at regular increments of deflection. The deflection +readings should be to the nearest 0.01 inch. To avoid error due +to parallax, the readings may be taken by means of a reading +telescope about ten feet distant and approximately on a level +with the wire. A mirror fastened to the scale will increase the +accuracy of the readings if the telescope is not used. As in all +tests on timber, the strain must be continuous to rupture, not +intermittent, and readings must be taken "on the fly." The +weighing beam is kept balanced after the yield point is reached +and the maximum load, and at least one point beyond it, noted.</p> + +<p><i>Log of the test</i>: The proper log sheet for this test consists +of a piece of cross-section paper with space at the margin for +notes. (<a href="#fig32">See Fig. 32</a>.) The load in some convenient unit (1,000 to +10,000 pounds, depending upon the dimensions of the specimen) is +entered on the ordinates, the deflection in tenths of an inch on +the abscissæ. The increments of load should be chosen so as to +<a name="pg098"></a> +furnish about ten points on the stress-strain diagram below the +elastic limit.</p> + +<p>As the readings of the wire on the scale are made they are +entered directly in their proper place on the cross-section +paper. In many cases a test should be continued until complete +failure results. The points where the various failures occur are +indicated on the stress-strain diagram. A brief description of +the failure is made on the margin of the log sheet, and the form +traced on the sketches.</p> + +<p><i>Disposal of the specimen</i>: Two one-inch sections are cut from +the region of failure to be used in determining the moisture +content. (<a href="#III_04">See Moisture Determination, page 90</a>.) A two-inch section +may be cut for subsequent reference and identification, and +possible microscopic study. The remainder of the beam may be cut +into small beams and compression pieces.</p> + +<p><i>Calculating the results</i>: The formulæ used in calculating the +results of tests on large rectangular simple beams loaded at +third points of the span are as follows:</p> + +<center> +<table summary="text"> +<tbody> +<tr><td><br></td> <td><br></td> <td><br></td><td> 0.75 <i>P</i> </td></tr> +<tr><td> (1) </td><td> <i>J</i> </td> <td> = </td><td> --------</td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>b h</i> </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>l</i> (<i>P</i><sub><small>1</small></sub> + 0.75 <i>W</i>)</td></tr> +<tr><td> (2) </td><td> <i>r</i> </td> <td> = </td><td> --------------------</td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>b h</i><sup><small>2</small></sup></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>l</i> (<i>P</i> + 0.75 <i>W</i>) </td></tr> +<tr><td> (3) </td><td> <i>R</i> </td> <td> = </td><td> ---------------- </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>b h</i><sup><small>2</small></sup></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>P</i><sub><small>1</small></sub><i>l</i><small><sup>3</sup></small></td></tr> +<tr><td> (4) </td><td> <i>E</i> </td> <td> = </td><td>---------------</td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> 4.7 <i>D b h</i> <small><sup>3</sup></small></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> 0.87 <i>P</i> <sub><small>1</small></sub> <i>D</i> </td></tr> +<tr><td> (5) </td><td> <i>S</i> </td> <td> = </td><td>--------------</td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> 2 <i>V</i> </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td><br></td> <td> <i>b, h, l</i></td> <td> = </td><td style="text-align: left;"> breadth, height, and span of specimen, inches. </td></tr> +<tr><td><br></td> <td> <i>D</i> </td> <td> = </td><td style="text-align: left;"> total deflection at elastic limit, inches. </td></tr> +<tr><td><br></td> <td> <i>P</i> </td> <td> = </td><td style="text-align: left;"> maximum load, pounds. </td></tr> +<tr><td><br></td> <td> <i>P</i><sub><small>1</small></sub> </td><td> = </td><td style="text-align: left;"> load at elastic limit, pounds. </td></tr> +<tr><td><br></td> <td> <i>E</i> </td> <td> = </td><td style="text-align: left;"> modulus of elasticity, pounds per square inch. </td></tr> +<tr><td><br></td> <td> <i>r</i> </td> <td> = </td><td style="text-align: left;"> fibre stress at elastic limit, pounds per sq. inch. </td></tr> +<tr><td><br></td> <td> <i>R</i> </td> <td> = </td><td style="text-align: left;"> modulus of rupture, pounds per square inch. </td></tr> +<tr><td><br></td> <td> <i>S</i> </td> <td> = </td><td style="text-align: left;"> elastic resilience or work to elastic limit, inch-pounds per cu. in. </td></tr> +<tr><td><br></td> <td> <i>J</i> </td> <td> = </td><td style="text-align: left;"> greatest calculated longitudinal shear, pounds per square inch. </td></tr> +<tr><td><br></td> <td> <i>V</i> </td> <td> = </td><td style="text-align: left;"> volume of beam, cubic inches. </td></tr> +<tr><td><br></td> <td> <i>W</i> </td> <td> = </td><td style="text-align: left;"> weight of the beam. </td></tr> +</tbody> +</table> +</center> + +<a name="pg099"></a> + +<p>In large beams the weight should be taken into account in +calculating the fibre stress. In (2) and (3) three-fourths of +the weight of the beam is added to the load for this reason.</p> + +<a name="III_08"></a> +<h3>BENDING SMALL BEAMS</h3> + +<p><i>Apparatus</i>: An ordinary static bending machine, a steel I-beam +bearing two adjustable knife-edge supports to rest on the +platform, and a special deflectometer, are required. (<a href="#fig31">See Fig. +31</a>.)</p> + +<p class="ctr"><img src="images/fig31.jpg" alt="Figure 31" id="fig31" /></p> +<p class="imgtitle">Figure 31</p> +<p class="imgtext"> Static bending test on small beam. Note +the use of the deflectometer with indicator and dial for +measuring the deflection; also roller bearings between beam and +supports.</p> + +<p><i>Preparing the material</i>: The specimens may be of any convenient +size, though beams 2" × 2" × 30" tested over a 28-inch span, are +considered best. The beams are surfaced on all four sides, care +being taken that they are not damaged by the rollers of the +surfacing machine. Material for these tests is sometimes cut +from large beams after failure. The specimens are carefully +weighed in grams, and all dimensions measured to the nearest +0.01 inch. If to be tested in a green or fresh condition the +<a name="pg100"></a> +specimens should be kept in a damp box or covered with moist +sawdust until needed. No defects should be allowed in these +specimens.</p> + +<p><i>Marking and sketching</i>: Sketches are made of each end of the +specimen to show the character of the growth, and after testing, +the manner of failure is shown for all four sides. In obtaining +data regarding the rate of growth and the proportion of late +wood the same procedure is followed as with large beams.</p> + +<p><i>Adjusting specimen in machine</i>: The beam should be correctly +centred in the machine and each end should have a plate with +roller bearings between it and the support. Centre loading is +used. Between the movable head of the machine and the specimen +is placed a bearing block of maple or other hard wood, the lower +surface of which is curved in a direction along the beam, the +curvature of which should be slightly less than that of the beam +at rupture, in order to prevent the edges from crushing into the +fibres of the test piece.</p> + +<p><i>Measuring the deflection</i>: The method of measuring deflection +of large beams can be used for small sizes, but because of the +shortness of the span and consequent slight deformation in the +latter, it is hardly accurate enough for good work. The special +deflectometer shown in Fig. 31 allows closer reading, as it +magnifies the deflection ten times. It rests on two small nails +driven in the beam on the neutral plane and vertically above the +supports. The fine wire on the wheel at the base of the +indicator is attached to another small nail driven in the beam +on the neutral plane midway between the end nails. All three +nails should be in place before the beam is put into the +machine. The indicator is adjustable by means of a thumb-screw +at the base and is set at zero before the load is applied. +Deflections are read to the nearest 0.001 inch. For rate of +application of load see Speed of Testing Machine, <a href="#pg092">page 92</a>. The +speed should be uniform from start to finish without stopping. +Readings must be made "on the fly."</p> + +<p><i>Log of the test</i>: The log sheets used for small beams (see Fig. +32) are the same as for large sizes and the procedure is +practically identical. The stress-strain diagram is continued to +or beyond the maximum load, and in a portion of the tests should +be continued to six-inch deflection or until the specimen fails +to support a load of 200 pounds. Deflection readings for equal +increments of <a name="pg102"></a> load are taken until well beyond the elastic +limit, after which the scale beam is kept balanced and the load +read for each 0.1 inch deflection. The load and deflection at +first failure, the maximum load, and any points of sudden change +should be shown on the diagram, even though they do not occur at +one of the regular points. A brief description of the failure +and the nature of any defects is entered on the log sheet.</p> + +<a name="pg101"></a> + +<p class="ctr"><img src="images/fig32.jpg" alt="Figure 32" id="fig32" /></p> +<p class="imgtitle">Figure 32</p> +<p class="imgtext"> Sample log sheet, giving full details +of a transverse bending test on a small pine beam.</p> + +<p><i>Calculating the results</i>: The formulæ used in calculating the +results of tests on small rectangular simple beams are as +follows:</p> + +<center> +<table summary="text"> +<tbody> +<tr><td><br></td> <td><br></td> <td><br></td><td> 0.75 <i>P</i> </td></tr> +<tr><td> (1) </td><td> <i>J</i> </td><td> = </td> <td> -------- </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>b h</i> </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> 1.5 <i>P</i><sub><small>1</small></sub> <i>l</i> </td></tr> +<tr><td> (2) </td><td> <i>r</i> </td><td> = </td> <td> ------------ </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>b h</i><sup><small>2</small></sup></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> 1.5 <i>P l</i> </td></tr> +<tr><td> (3) </td><td> <i>R</i> </td><td> = </td> <td> --------- </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>b h</i><sup><small>2</small></sup></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>P</i><sub><small>1</small></sub> <i>l</i> <sup><small>3</small></sup><br></td></tr> +<tr><td> (4) </td><td> <i>E</i> </td><td> = </td> <td> ------------ </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> 4 <i>D b h</i><sup><small>3</small></sup></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>P</i><sub><small>1</small></sub> <i>D</i> </td></tr> +<tr><td> (5) </td><td> <i>S</i> </td><td> = </td> <td> --------- </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> 2 <i>V</i> </td></tr> +</tbody> +</table> +</center> + +<p>The same legend is used as on <a href="#pg098">page 98</a>. The weight of +the beam itself is disregarded.</p> + +<a name="III_09"></a> +<h3>ENDWISE COMPRESSION</h3> + +<p><i>Apparatus</i>: An ordinary static testing machine and a +compressometer are required. (<a href="#fig33">See Fig. 33</a>.)</p> + +<p class="ctr"><img src="images/fig33.jpg" alt="Figure 33" id="fig33" /></p> +<p class="imgtitle">Figure 33</p> +<p class="imgtext"> Endwise compression test, showing +method of measuring the deformation by means of a +compressometer.</p> + +<p><i>Preparing the material</i>: Two classes of specimens are commonly +used, namely, (1) posts 24 inches in length, and (2) small clear +blocks approximately 2" × 2" × 8". The specimens are surfaced on +all four sides and both ends squared smoothly and evenly. They +are carefully weighed, measured, rate of growth and proportion +of late wood determined, as in bending tests. After the test a +moisture section is cut and weighed. Ordinarily these specimens +should be free from defects.</p> + +<p><i>Sketching</i>: Sketches are made of each end of the specimens to +show the character of the growth. After testing, the manner of +failure is shown for all four sides, and the various parts of +the failure are numbered in the order of their occurrence.</p> + +<p><i>Adjusting specimen in machine</i>: The compressometer collars are +adjusted, the distance between them being 20 inches for the +posts and 6 inches for the blocks. If the two ends of the blocks +are not exactly parallel a ball-and-socket block can be placed +between <a name="pg103"></a> the upper end of the specimen and the movable head of +the machine to overcome the irregularity. If the blocks are true +they can simply be stood on end upon the platform and the +movable head allowed to press directly upon the upper end.</p> + +<p><i>Measuring the deformation</i>: The deformation is measured by a +compressometer. (<a href="#fig33">See Fig. 33</a>.) The latter registers to 0.001 +inch. In the case of posts the compression between the collars +is communicated to the four points on the arms by means of brass +rods; with short blocks, as in <a href="#fig33">Fig. 33</a>, the points of the arms +are in direct contact with the collars. The operator lowers the +fulcrum of the apparatus by moving the micrometer screws at such +a rate that the set-screw in the rear end of the upper lever is +kept barely touching the fixed arm below it, being guided by a +bell operated by electric contact.</p> + +<p><i>Log of the test</i>: The load is applied continuously at a uniform +rate of speed. (See Speed of Testing Maching, <a href="#pg092">page 92</a>.) <a name="pg104"></a> Readings +are taken from the scale of the compressometer at regular +increments of either load or compression. The stress-strain +diagram is continued to at least one deformation point beyond +the maximum load, and in event of sudden failure, the direction +of the curve beyond the maximum point is indicated. A brief +description of the failure is entered on the log sheet. (<a href="#fig34">See +Fig. 34</a>.)</p> + +<a name="pg105"></a> + +<p class="ctr"><img src="images/fig34.jpg" alt="Figure 34" id="fig34" /></p> +<p class="imgtitle">Figure 34</p> +<p class="imgtext"> Sample log sheet of an endwise +compression test on a short pine column.</p> + +<p>In short specimens the failure usually occurs in one or several +planes diagonal to the axis of the specimen. If the ends are +more moist than the middle a crushing may occur on the extreme +ends in a horizontal plane. Such a test is not valid and should +always be culled. If the grain is diagonal or the stress is +unevenly applied a diagonal shear may occur from top to bottom +of the test specimen. Such tests are also invalid and should be +culled. When the plane (or several planes) of failure occurs +through the body of the specimen the test is valid. It may +sometimes be advantageous to allow the extreme ends to dry +slightly before testing in order to bring the planes of failure +within the body. This is a perfectly legitimate procedure +provided no drying is allowed from the sides of the specimen, +and the moisture disk is cut from the region of failure.</p> + +<p><i>Calculating the results:</i> The formulæ used in calculating the +results of tests on endwise compression are as follows:</p> + +<center> +<table summary="text"> +<tbody> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>P</i> </td></tr> +<tr><td> (1) </td><td> <i>C</i> </td><td> = </td><td> ----- </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>A</i> </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>P</i><sub><small>1</small></sub></td></tr> +<tr><td> (2) </td><td> <i>c</i> </td><td> = </td><td> ------- </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>A</i> </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>P</i><sub><small>1</small></sub> <i>l</i> </td></tr> +<tr><td> (3) </td><td> <i>E</i> </td><td> = </td><td> --------- </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>A D</i> </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> <i>P D</i> </td></tr> +<tr><td> (4) </td><td> <i>S</i> </td><td> = </td><td> ----- </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td> 2 <i>V</i> </td></tr> +<tr><td><br></td> <td><br></td> <td><br></td><td><br></td></tr> +<tr><td><br></td> <td> <i>C</i> </td><td> = </td><td style="text-align: left;"> crushing strength, pounds per square inch. </td></tr> +<tr><td><br></td> <td> <i>c</i> </td><td> = </td><td style="text-align: left;"> fibre strength at elastic limit, pounds per square inch. </td></tr> +<tr><td><br></td> <td> <i>A</i> </td><td> = </td><td style="text-align: left;"> area of cross section, square inches. </td></tr> +<tr><td><br></td> <td> <i>l</i> </td><td> = </td><td style="text-align: left;"> distance between centres of collars, inches. </td></tr> +<tr><td><br></td> <td> <i>D</i> </td><td> = </td><td style="text-align: left;"> total shortening at elastic limit, inches. </td></tr> +<tr><td><br></td> <td> <i>V</i> </td><td> = </td><td style="text-align: left;"> volume of specimen, cubic inches. </td></tr> +</tbody> +</table> +</center> + +<p>Remainder of legend as on <a href="#pg098">page 98</a>.</p> + +<a name="III_10"></a> +<h3>COMPRESSION ACROSS THE GRAIN</h3> + +<p><i>Apparatus</i>: An ordinary static testing machine, a bearing +plate, and a deflectometer are required. (<a href="#fig35">See Fig. 35</a>.)</p> + +<p class="ctr"><img src="images/fig35.jpg" alt="Figure 35" id="fig35" /></p> +<p class="imgtitle">Figure 35</p> +<p class="imgtext"> Compression across the grain. Note +method of measuring the deformation by means of a +deflectomoter.</p> + +<a name="pg106"></a> + +<p><i>Preparing the material</i>: Two classes of specimens are used, +namely, (1) sections of commercial sizes of ties, beams, and +other timbers, and (2) small, clear specimens with the length +several times the width. Sometimes small cubes are tested, but +the results are hardly applicable to conditions in practice. In +(2) the sides are surfaced and the ends squared. The specimens +are then carefully measured and weighed, defects noted, rate of +growth and proportion of late wood determined, as in bending +tests. (<a href="#pg095">See page 95</a>.) After the test a +moisture section is cut and weighed.</p> + +<p><i>Sketching</i>: Sketches are made as in endwise compression tests. +(<a href="#pg102">See page 102</a>.)</p> + +<p><i>Adjusting specimen in machine</i>: The specimen is laid +horizontally upon the platform of the machine and a steel +bearing plate placed on its upper surface immediately beneath +the centre of the movable head. For the larger specimens this +plate is six inches wide; for the smaller sizes, two inches +wide. The plate in all cases projects over the edges of the test +piece, and in no case should the length of the latter be less +than four times the width of the plate.</p> + +<a name="pg107"></a> + +<p><i>Measuring the deformation</i>: The compression is measured by +means of a deflectometer (<a href="#fig35">see Fig. 35</a>), which, after the first +increment of load is applied, is adjusted (by means of a small +set screw) to read zero. The actual downward motion of the +movable head (corresponding to the compression of the specimen) +is multiplied ten times on the scale from which the readings are +made.</p> + +<p><i>Log of the test</i>: The load is applied continuously and at +uniform speed (see Speed of Testing Machine, <a href="#pg092">page 92</a>), until well +beyond the elastic limit. The compression readings are taken at +regular load increments and entered on the cross-section paper +in the usual way. Usually there is no real maximum load in this +case, as the strength continually increases as the fibres are +crushed more compactly together.</p> + +<p><i>Calculating the results</i>: Ordinarily only the fibre stress at +the elastic limit (<i>c</i>) is computed. It is equal to the load at +elastic limit (P<sub><small>1</small></sub>) divided by the area under the plate (<i>B</i>).</p> + +<center> +<table summary="text"> +<tbody> +<tr><td rowspan="3"><big><big><big><big>(</big></big></big></big></td><td><br></td> <td><br></td><td> <i>P</i><sub><small>1</small></sub> </td><td rowspan="3"> <big><big><big><big>)</big></big></big></big></td></tr> +<tr> <td> <i>c</i> </td> <td> = </td> <td> ------- </td></tr> +<tr> <td><br></td> <td><br></td><td> <i>B</i> </td></tr> +</tbody> +</table> +</center> + +<a name="III_11"></a> +<h3>SHEAR ALONG THE GRAIN</h3> + +<p><i>Apparatus</i>: An ordinary static testing machine and a special +tool designed for producing single shear are required. (<a href="#fig36">See +Figs. 36</a> and <a href="#fig37">37</a>.) This shearing apparatus consists of a solid +steel frame with set screws for clamping the block within it +firmly in a vertical position. In the centre of the frame is a +vertical slot in which a square-edged steel plate slides freely. +When the testing block is in position, this plate impinges +squarely along the upper surface of the tenon or lip, which, as +vertical pressure is applied, shears off.</p> + +<p class="ctr"><img src="images/fig36.jpg" alt="Figure 36" id="fig36" /></p> +<p class="imgtitle">Figure 36</p> +<p class="imgtext"> Vertical section of shearing tool.</p> + +<p class="ctr"><img src="images/fig37.jpg" alt="Figure 37" id="fig37" /></p> +<p class="imgtitle">Figure 37</p> +<p class="imgtext"> Front view of shearing tool with test +specimen and steel plate in position for testing.</p> + +<p><i>Preparing the material</i>: The specimens are usually in the form +of small, clear, straight-grained blocks with a projecting tenon +or lip to be sheared off. Two common forms and sizes are shown +in Figure 38. Part of the blocks are cut so that the shearing +surface is parallel to the growth rings, or tangential; others +at <a name="pg109"></a> right angles to the growth rings, or radial. It is important +that the upper surface of the tenon or lip be sawed exactly +parallel to the base of the block. When the form with a tenon is +used the under cut is extended a short distance horizontally +into the block to prevent any compression from below.</p> + +<a name="pg108"></a> + +<p class="ctr"><img src="images/fig38.jpg" alt="Figure 38" id="fig38" /></p> +<p class="imgtitle">Figure 38</p> +<p class="imgtext"> Two forms of shear test specimens.</p> + +<p>In designing a shearing specimen it is necessary to take into +consideration the proportions of the area of shear, since, if +the length of the portion to be sheared off is too great in the +direction of the shearing face, failure would occur by +compression before the piece would shear. Inasmuch as the +endwise compressive strength is sometimes not more than five +times the shearing strength, the shearing surface should be less +than five times the surface to which the load is applied. This +condition is fulfilled in the specimens illustrated.</p> + +<p>Shearing specimens are frequently cut from beams after testing. +In this case the specific gravity (dry), proportion of late +wood, and rate of growth are assumed to be the same as already +<a name="pg110"></a> +recorded for the beams. In specimens not so taken, these +quantities are determined in the usual way. The sheared-off +portion is used for a moisture section.</p> + +<p><i>Adjusting specimen in machine</i>: The test specimen is placed in +the shearing apparatus with the tenon or lip under the sliding +plate, which is centred under the movable head of the machine. +(<a href="#fig39">See Fig. 39</a>.) In order to reduce to a minimum the friction due +to the lateral pressure of the plate against the bearings of the +slot, the apparatus is sometimes placed upon several parallel +steel rods to form a roller base. A slight initial load is +applied to take up the lost motion of the machinery, and the +beam balanced.</p> + +<p class="ctr"><img src="images/fig39.jpg" alt="Figure 39" id="fig39" /></p> +<p class="imgtitle">Figure 39</p> +<p class="imgtext"> Making a shearing test.</p> + +<p><i>Log of the test</i>: The load is applied continuously and at a +uniform rate until failure, but no deformations are measured. +The points noted are the maximum load and the length of time +required to reach it. Sketches are made of the failure. If the +failure is not pure shear the test is culled.</p> + +<p>The shearing strength per square inch is found by dividing the +maximum load by the cross-sectional area.</p> + +<center> +<table summary="text"> +<tbody> +<tr><td rowspan="3"><big><big><big><big>(</big></big></big></big></td><td><br></td> <td><br></td><td> <i>P</i> </td><td rowspan="3"> <big><big><big><big>)</big></big></big></big></td></tr> +<tr> <td> <i>Q</i> </td><td> = </td> <td> --- </td></tr> +<tr> <td><br></td> <td><br></td><td> <i>A</i> </td></tr> +</tbody> +</table> +</center> + +<a name="III_12"></a> +<h3>IMPACT TEST</h3> + +<p><i>Apparatus</i>: There are several types of impact testing +machines.<a name="fn59r"></a><a href="#fn59"><sup><small>59</small></sup></a> One of the simplest and most efficient for use +with wood is illustrated in <a href="#fig40">Figure 40</a>. The base of the machine +is 7 feet long, 2.5 feet wide at the centre, and weighs 3,500 +pounds. Two upright columns, each 8 feet long, act as guides for +the striking head. At the top of the column is the hoisting +mechanism for raising or lowering the striking weights. The +power for operating the machine is furnished by a motor set on +the top. The hoisting-mechanism is all controlled by a single +operating lever, shown on the side of the column, whereby the +striking weight may be raised, lowered, or stopped at the will +of the operator. There is an automatic safety device for +stopping the machine when the weight reaches the top.</p> + +<a name="pg111"></a> + +<p class="ctr"><img src="images/fig40.jpg" alt="Figure 40" id="fig40" /></p> +<p class="imgtitle">Figure 40</p> +<p class="imgtext"> Impact testing machine.</p> + +<p>The weight is lifted by a chain, one end of which passes over a +<a name="pg112"></a> +sprocket wheel in the hoisting mechanism. On the lower end of +the chain is hung an electro-magnet of sufficient magnetic +strength to support the heaviest striking weights. When it is +desired to drop the striking weight the electric current is +broken and reversed by means of an automatic switch and current +breaker. The height of drop may be regulated by setting at the +desired height on one of the columns a tripping pin which throws +the switch on the magnet and so breaks and reverses the current.</p> + +<p>There are four striking weights, weighing respectively 50, 100, +250, and 500 pounds, any one of which may be used, depending +upon the desired energy of blow. When used for compression tests +a flat steel head six inches in diameter is screwed into the +lower end of the weight. For transverse tests, a well-rounded +knife edge is screwed into the weight in place of the flat head. +Knife edges for supporting the ends of the specimen to be +tested, are securely bolted to the base of the machine.</p> + +<p>The record of the behavior of the specimen at time of impact is +traced upon a revolving drum by a pencil fixed in the striking +head. (<a href="#fig41">See Fig. 41</a>.) When a drop is made the pencil comes in +contact with the drum and is held in place by a spring. The drum +is revolved very slowly, either automatically or by hand. The +speed of the drum can be recorded by a pencil in the end of a +tuning fork which gives a known number of vibrations per second.</p> + +<p class="ctr"><img src="images/fig41.jpg" alt="Figure 41" id="fig41" /></p> +<p class="imgtitle">Figure 41</p> +<p class="imgtext"> Drum record of impact bending test.</p> + +<p>One size of this machine will handle specimens for transverse +tests 9 inches wide and 6-foot span; the other, 12 inches wide +and 8-foot span. For compression tests a free fall of about 6.5 +feet may be obtained. For transverse tests the fall is a little +less, depending upon the size of the specimen.</p> + +<p>The machine is calibrated by dropping the hammer upon a copper +cylinder. The axial compression of the plug is noted. The energy +used in static tests to produce this axial compression under +stress in a like piece of metal is determined. The external +energy of the blow (<i>i.e.</i>, the weight of the hammer × the +height of drop) is compared with the energy used in static tests +at equal amounts of compression. For instance:</p> + +<center> +<table summary="text"> +<tbody> +<tr><td style="text-align: left;"> Energy delivered, impact test</td><td style="width: 20px;"></td><td style="text-align: right;"> 35,000 inch-pounds</td></tr> +<tr><td style="text-align: left;"> Energy computed from static test</td><td style="width: 20px;"></td><td style="text-align: right;"> 26,400 inch-pounds</td></tr> +<tr><td style="text-align: left;"> Efficiency of blow of hammer</td><td style="width: 20px;"></td><td style="text-align: right;"> 75.3 per cent.</td></tr> +</tbody> +</table> +</center> + +<a name="pg113"></a> + +<p><i>Preparing the material</i>: The material used in making impact +tests is of the same size and prepared in the same way as for +static bending and compression tests. Bending in impact tests is +more commonly used than compression, and small beams with +28-inch span are usually employed.</p> + +<p><i>Method</i>: In making an impact bending test the hammer is allowed +to rest upon the specimen and a zero or datum line is drawn. The +hammer is then dropped from increasing heights and drum records +taken until first failure. The first drop is one inch and the +increase is by increments of one inch until a height of ten +inches is reached, after which increments of two inches are used +until complete failure occurs or 6-inch deflection is secured.</p> + +<a name="pg114"></a> + +<p>The 50-pound hammer is used when with drops up to 68 inches it +is reasonably certain it will produce complete failure or 6-inch +deflection in the case of all specimens of a species; for all +other species a 100-pound hammer is used.</p> + +<p><i>Results</i>: The tracing on the drum (<a href="#fig41">see Fig. 41</a>) represents the +actual deflection of the stick and the subsequent rebounds for +each drop. The distance from the lowest point in each case to +the datum line is measured and its square in tenths of a square +inch entered as an abscissa on cross-section paper, with the +height of drop in inches as the ordinate. The elastic limit is +that point on the diagram where the square of the deflection +begins to increase more rapidly than the height of drop. The +difference between the datum line and the final resting point +after each drop represents the set the material has received.</p> + +<p>The formulæ used in calculating the results of impact tests in +bending when the load is applied at the centre up to the elastic +limit are as follows:</p> + +<center> +<table summary="text"> +<tbody> +<tr><td><br></td><td><br></td><td><br></td><td> 3 <i>W H l</i> </td></tr> +<tr><td> (1) </td><td> <i>r</i> </td><td> = </td><td> ----------- </td></tr> +<tr><td><br></td><td><br></td><td><br></td><td> <i>D b h</i><sup><small>2</small></sup> </td></tr> +<tr><td><br></td><td><br></td><td><br></td><td><br></td></tr> +<tr><td><br></td><td><br></td><td><br></td><td> <i>F S l</i><sup><small>2</small></sup> </td></tr> +<tr><td> (2) </td><td> <i>E</i> </td><td> = </td><td> ----------- </td></tr> +<tr><td><br></td><td><br></td><td><br></td><td> 6 <i>D h</i> </td></tr> +<tr><td><br></td><td><br></td><td><br></td><td><br></td></tr> +<tr><td><br></td><td><br></td><td><br></td><td> <i>W H</i> </td></tr> +<tr><td> (3) </td><td> <i>S</i> </td><td> = </td><td> ------- </td></tr> +<tr><td><br></td><td><br></td><td><br></td><td> <i>l b h</i> </td></tr> +<tr><td><br></td><td><br></td><td><br></td><td><br></td></tr> +<tr><td><br></td><td> <i>H</i> </td><td> = </td><td style="text-align: left;"> height of drop of hammer, including deflection, inches. </td></tr> +<tr><td><br></td><td> <i>S</i> </td><td> = </td><td style="text-align: left;"> modulus of elastic resilience, inch-pounds per cubic inch. </td></tr> +<tr><td><br></td><td> <i>W</i> </td><td> = </td><td style="text-align: left;"> weight of hammer, pounds. </td></tr> +</tbody> +</table> +</center> + +<p>Remainder of legend as on <a href="#pg098">page 98</a>.</p> + +<a name="III_13"></a> +<h3>HARDNESS TEST: ABRASION AND INDENTATION</h3> + +<p><i>Abrasion</i>: The machine used by the U.S. Forest Service is a +modified form of the Dorry abrasion machine. (<a href="#fig42">See Fig. 42</a>.) Upon +the revolving horizontal disk is glued a commercial sandpaper, +known as garnet paper, which is commonly employed in factories +in finishing wood.</p> + +<a name="pg115"></a> + +<p class="ctr"><img src="images/fig42.jpg" alt="Figure 42" id="fig42" /></p> +<p class="imgtitle">Figure 42</p> +<p class="imgtext"> Abrasion machine for testing the +wearing qualities of woods.</p> + +<p>A small block of the wood to be tested is fixed in one clamp and +a similar block of some wood chosen as a standard, as sugar +maple, at 10 per cent moisture, in the opposite, and held +against the same zone of sandpaper by a weight of 26 pounds +each. The size of the section under abrasion for each specimen +is 2" × 2". <a name="pg116"></a> The conditions for wear are the same for both +specimens. The speed of rotation is 68 revolutions a minute.</p> + +<p>The test is continued until the standard specimen is worn a +specified amount, which varies with the kind of wood under test. +A comparison of the wear of the two blocks affords a fair idea +of their relative resistance to abrasion.</p> + +<p>Another method makes use of a sand blast to abrade the woods and +is the one employed in New South Wales.<a name="fn60r"></a><a href="#fn60"><sup><small>60</small></sup></a> The apparatus +consists essentially of a nozzle through which sand can be +propelled at a high velocity against the test specimen by means +of a steam jet.</p> + +<p>The wood to be tested is cut into blocks 3" × 3" × 1', and these +are weighed to the nearest grain just before placing in the +apparatus. Steam from the boiler at a pressure of about 43 +pounds per square inch is ejected from a nozzle in such a way +that particles of fine quartz sand are caught up and thrown +violently against the block which is being rotated. Only +superheated steam strikes the block, thus leaving the wood dry. +The test is continued for two minutes, after which the specimen +is removed and immediately weighed.</p> + +<p>By comparison with the original weight the loss from <a name="pg117"></a> abrasion is +determined, and by comparison with a certain wood chosen as a +standard, a coefficient of wear-resistance can be obtained. The +amount of wear will vary more or less according to the surface +exposed, and in these tests quarter-sawed material was used with +the edge grain to the blast.</p> + +<p><i>Indentation</i>: The tool used for this test consists of a punch +with a hemispherical end or steel ball having a diameter of +0.444 inch, giving a surface area of one-fourth square inch. It +is fitted with a guard plate, which works loosely until the +penetration has progressed to a depth of 0.222 inch, whereupon +it tightens. (<a href="#fig43">See Fig. 43</a>.) The effect is that of sinking a ball +half its diameter into the specimen. This apparatus is fitted +into the movable head of the static testing machine.</p> + +<p class="ctr"><img src="images/fig43.jpg" alt="Figure 43" id="fig43" /></p> +<p class="imgtitle">Figure 43</p> +<p class="imgtext"> Design of tool for testing the hardness +of woods by indentation.</p> + +<p>The wood to be tested is cut square with the grain into +rectangular blocks measuring 2" × 2" × 6". A block is placed on +the platform and the end of the punch forced into the wood at +the rate of 0.25 inch per minute. The operator keeps moving the +small handle of the guard plate back and forth until it +tightens. At this instant the load is read and recorded.</p> + +<p>Two penetrations each are made on the tangential and radial +surfaces, and one on each end of every specimen tested.</p> + +<p>In choosing the places on the block for the indentations, effort +should be made to get a fair average of heartwood and sapwood, +fine and coarse grain, early and late wood.</p> + +<p>Another method of testing by indentation involves the use <a name="pg118"></a> of a +right-angled cone instead of a ball. For details of this test as +used in New South Wales see <i>loc. cit.</i>, pp. 86-87. + +<a name="III_14"></a> +<h3>CLEAVAGE TEST</h3> + +<p>A static testing machine and a special cleavage testing device +are required. (<a href="#fig44">See Fig. 44</a>.) The latter consists essentially of +two hooks, one of which is suspended from the centre of the top +of the cage, the other extended above the movable head.</p> + +<p class="ctr"><img src="images/fig44.jpg" alt="Figure 44" id="fig44" /></p> +<p class="imgtitle">Figure 44</p> +<p class="imgtext"> Design of tool for cleavage test.</p> + +<p>The specimens are 2" × 2" × 3.75". At one end a one-inch hole is +bored, with its centre equidistant from the two sides and 0.25 +inch from the end. (<a href="#fig45">See Fig. 45</a>.) This makes the cross section +to be tested 2" × 3". Some of the blocks are cut radially and +some tangentially, as indicated in the figure.</p> + +<p class="ctr"><img src="images/fig45.jpg" alt="Figure 45" id="fig45" /></p> +<p class="imgtitle">Figure 45</p> +<p class="imgtext"> Design of cleavage test specimen.</p> + +<p>The free ends of the hooks are fitted into the notch in the end +of the specimen. The movable head of the machine is then made to +descend at the rate of 0.25 inch per minute, pulling apart the +hooks and splitting the block. The maximum load only is taken +and the result expressed in pounds per square inch of width. A +piece one-half inch thick is split off parallel to the failure +and used for moisture determination. + +<a name="III_15"></a> +<h3>TENSION TEST PARALLEL TO THE GRAIN</h3> + +<p>Since the tensile strength of wood parallel to the grain is +greater than the compressive strength, and exceedingly greater +than the shearing strength, it is very difficult to make +satisfactory tension tests, as the head and shoulders of the +test specimen (which is subjected <a name="pg119"></a> to both compression and shear) +must be stronger than the portion subjected to a pure tensile +stress.</p> + +<p>Various designs of test specimens have been made. The one first +employed by the Division of Forestry<a name="fn61r"></a><a href="#fn61"><sup><small>61</small></sup></a> was prepared as +follows: Sticks were cut measuring 1.5" × 2.5" × 16". The +thickness at the centre was then reduced to three-eighths of an +inch by cutting out circular segments with a band saw. This left +a breaking section of 2.5" × 0.375". Care was taken to cut the +specimen as nearly parallel to the grain as possible, so that +its failure would occur in a condition of pure tension. The +specimen was then placed between the plane wedge-shaped steel +grips of the cage and the movable head of the static machine and +pulled in two. Only the maximum load was recorded. (<a href="#fig46">See Fig. 46</a>, +No. 1.)</p> + +<p class="ctr"><img src="images/fig46.jpg" alt="Figure 46" id="fig46" /></p> +<p class="imgtitle">Figure 46</p> +<p class="imgtext"> Designs of tension test specimens used +in United States.</p> + +<a name="pg120"></a> + +<p>The difficulty of making such tests compared with the minor +importance of the results is so great that they are at present +omitted by the U.S. Forest Service. A form of specimen is +suggested, however, and is as follows: "A rod of wood about one +inch in diameter is bored by a hollow drill from the stick to be +tested. The ends of this rod are inserted and glued in +corresponding holes in permanent hardwood wedges. The specimen +is then submitted to the ordinary tension test. The broken ends +are punched from the wedges."<a name="fn62r"></a><a href="#fn62"><sup><small>62</small></sup></a> (See Fig. 46, No. 2.)</p> + +<p>The form used by the Department of Forestry of New South +Wales<a name="fn63r"></a><a href="#fn63"><sup><small>63</small></sup></a> is as shown in Fig. 47. The specimen has a total +length of 41 inches and is circular in cross section. On each +end is a head 4 inches in diameter and 7 inches long. Below each +head is a shoulder 8.5 inches long, which tapers from a diameter +of 2.75 inches to 1.25 inches. In the middle is a cylindrical +portion 1.25 inches in diameter and 10 inches long.</p> + +<p class="ctr"><img src="images/fig47.jpg" alt="Figure 47" id="fig47" /></p> +<p class="imgtitle">Figure 47</p> +<p class="imgtext"> Design of tension test specimen used in +New South Wales.</p> + +<p>In making the test the specimen is fitted in the machine, and an +extensometer attached to the middle portion and arranged to +record the extension between the gauge points 8 inches apart. +The area of the cross section then is 1.226 square inches, and +the tensile strength is equal to the total breaking load applied +divided by this area.</p> + +<a name="III_16"></a> +<h3>TENSION TEST AT RIGHT ANGLES TO THE GRAIN</h3> + +<p>A static testing machine and a special testing device (<a href="#fig48">see Fig. +48</a>) are required. The latter consists essentially of two double +<a name="pg121"></a> +hooks or clamps, one of which is suspended from the centre of +the top of the cage, the other extended above the movable head. +The specimens are 2" × 2" × 2.5". At each end a one-inch hole is +bored with its centre equidistant from the two sides and 0.25 +inch from the ends. This makes the cross section to be tested 1" + × 2".</p> + +<p class="ctr"><img src="images/fig48.jpg" alt="Figure 48" id="fig48" /></p> +<p class="imgtitle">Figure 48</p> +<p class="imgtext"> Design of tool and specimen for testing +tension at right angles to the grain.</p> + +<p>The free ends of the clamps are fitted into the notches in the +<a name="pg122"></a> +ends of the specimen. The movable head of the machine is then +made to descend at the rate of 0.25 inch per minute, pulling the +specimen in two at right angles to the grain. The maximum load +only is taken and the result expressed in pounds per inch of +width. A piece one-half inch thick is split off parallel to the +failure and used for moisture determination. + +<a name="III_17"></a> +<h3>TORSION TEST<a name="fn64r"></a><a href="#fn64"><sup><small>64</small></sup></a></h3> +<p><i>Apparatus</i>: The torsion test is made in a Riehle-Miller +torsional testing machine or its equivalent. (<a href="#fig49">See Fig. 49</a>.)</p> + +<p class="ctr"><img src="images/fig49.jpg" alt="Figure 49" id="fig49" /></p> +<p class="imgtitle">Figure 49</p> +<p class="imgtext"> Making a torsion test on hickory.</p> + +<p><i>Preparation of material</i>: The test pieces are cylindrical, 1.5 +inches in diameter and 18 inches gauge length, with squared ends +4 inches long joined to the cylindrical portion with a fillet. +The dimensions are carefully measured, and the usual data +obtained in regard to the rate of growth, proportion of late +wood, location <a name="pg123"></a> and kind of defects. The weight of the +cylindrical portion of the specimen is obtained after the test.</p> + +<p><i>Making the test</i>: After the specimen is fitted in the machine +the load is applied continuously at the rate of 22° per minute. +A troptometer is used in measuring the deformation. Readings are +made until failure occurs, the points being entered on the +cross-section paper. The character of the failure is described. +Moisture determinations are made by the disk method.</p> + +<p><i>Results</i>: The conditions of ultimate rupture due to torsion +appear not to be governed by definite mathematical laws; but +where the material is not overstrained, laws may be assumed +which are sufficiently exact for practical cases. The formulæ +commonly used for computations are as follows:</p> + +<center> +<table summary="text"> +<tbody> +<tr><td><br> </td><td><br></td> <td><br></td><td> 5.1 <i>M</i> </td></tr> +<tr><td> (1) </td><td> <i>T</i> </td><td> = </td><td> ------- </td></tr> +<tr><td><br> </td><td><br></td> <td><br></td><td> <i>c</i><sup><small>3</small></sup> </td></tr> +<tr><td><br> </td><td><br></td> <td><br></td><td><br></td></tr> +<tr><td><br> </td><td><br></td> <td><br></td><td> 114.6 <i>T f</i> </td></tr> +<tr><td> (2) </td><td> <i>G</i> </td><td> = </td><td> ----------- </td></tr> +<tr><td><br> </td><td><br></td> <td><br></td><td> <i>a c</i> </td></tr> +<tr><td><br> </td><td><br></td> <td><br></td><td><br></td></tr> +<tr><td><br> </td><td> <i>a</i> </td><td> = </td><td style="text-align: left;"> angle measured by troptometer at elastic limit, in degrees. </td></tr> +<tr><td><br> </td><td> <i>c</i> </td><td> = </td><td style="text-align: left;"> diameter of specimen, inches. </td></tr> +<tr><td><br> </td><td> <i>f</i> </td><td> = </td><td style="text-align: left;"> gauge length of specimen, inches. </td></tr> +<tr><td><br> </td><td> <i>G</i> </td><td> = </td><td style="text-align: left;"> modulus of elasticity in shear across the grain, pounds per square inch. </td></tr> +<tr><td><br> </td><td> <i>M</i> </td><td> = </td><td style="text-align: left;"> moment of torsion at elastic limit, inch-pounds. </td></tr> +<tr><td><br> </td><td> <i>T</i> </td><td> = </td><td style="text-align: left;"> outer fibre torsional stress at elastic limit, pounds per square inch. </td></tr> +</tbody> +</table> +</center> + +<a name="III_18"></a> +<h3>SPECIAL TESTS</h3> + +<a name="III_19"></a> +<h4><i>Spike-pulling Test</i></h4> + +<p>Spike-pulling tests apply to problems of railroad maintenance, +and the results are used to compare the spike-holding powers of +various woods, both untreated and treated with different +preservatives, and the efficiency of various forms of spikes. +Special tests are also made in which the spike is subjected to a +transverse load applied repetitively by a blow.</p> + +<p>For details of tests and results see:</p> + +<center> +<table summary="text"> +<tbody> +<tr><td style="text-align: left;"> Cir. 38, </td><td style="width: 20px;"><br></td><td style="text-align: left;"> U.S.F.S.: </td><td style="width: 20px;"><br></td><td style="text-align: left;"> Instructions to engineers of timber tests, p. 26. </td></tr> +<tr><td style="text-align: left;"> Cir. 46, </td><td style="width: 20px;"><br></td><td style="text-align: left;"> U.S.F.S.: </td><td style="width: 20px;"><br></td><td style="text-align: left;"> Holding force of railroad spikes in wooden ties. </td></tr> +<tr><td style="text-align: left;"> Bul. 118, </td><td style="width: 20px;"><br></td><td style="text-align: left;"> U.S.F.S.: </td><td style="width: 20px;"><br></td><td style="text-align: left;"> Prolonging the life of cross-ties, pp. 37-40. </td></tr> +</tbody> +</table> +</center> + +<a name="pg124"></a> + +<a name="III_20"></a> +<h4><i>Packing Boxes</i></h4> + +<p>Special tests on the strength of packing boxes of various woods +have been made by the U.S. Forest Service to determine the +merits of different kinds of woods as box material with the view +of substituting new kinds for the more expensive ones now in +use. The methods of tests consisted in applying a load along the +diagonal of a box, an action similar to that which occurs when a +box is dropped on one of its corners. The load was measured at +each one-fourth inch in deflection, and notes were made of the +primary and subsequent failures.</p> + +<p>For details of tests and results, see:</p> + +<center> +<table summary="text"> +<tbody> +<tr><td style="text-align: left;"> Cir. 47, </td><td style="width: 20px;"><br></td><td style="text-align: left;"> U.S.F.S.: </td><td style="width: 20px;"><br></td><td style="text-align: left;"> Strength of packing boxes of various woods. </td></tr> +<tr><td style="text-align: left;"> Cir. 214, </td><td style="width: 20px;"><br></td><td style="text-align: left;"> U.S.F.S.: </td><td style="width: 20px;"><br></td><td style="text-align: left;"> Tests of packing boxes of various forms. </td></tr> +</tbody> +</table> +</center> + +<a name="III_21"></a> +<h4><i>Vehicle and Implement Woods</i></h4> + +<p>Tests were made by the U.S. Forest Service to obtain a better +knowledge of the mechanical properties of the woods at present +used in the manufacture of vehicles and implements and of those +which might be substituted for them. Tests were made upon the +following materials: hickory buggy spokes (<a href="#fig05">see Fig. 5</a>); hickory +and red oak buggy shafts; wagon tongues; Douglas fir and +southern pine cultivator poles.</p> + +<p>Details of the tests and results may be found in:</p> + +<center> +<table summary="text"> +<tbody> +<tr><td style="text-align: left;"> Cir. 142, </td><td style="width: 20px;"><br></td><td style="text-align: left;"> U.S.F.S.: </td><td style="width: 20px;"><br></td><td style="text-align: left;"> Tests on vehicle and implement woods. </td></tr> +</tbody> +</table> +</center> + +<a name="III_22"></a> +<h4><i>Cross-arms</i></h4> + +<p>In tests by the U.S. Forest Service on cross-arms a special +apparatus was devised in which the load was distributed along +the arm as in actual practice. The load was applied by rods +passing through the pinholes in the arms. Nuts on these rods +pulled down on the wooden bearing-blocks shaped to fit the upper +side of the arm. The lower ends of these rods were attached to a +system of equalizing levers, so arranged that the load at each +pinhole would be the same. In all the tests the load was applied +vertically by means of the static machine.</p> + +<center> +<table summary="text"> +<tbody> +<tr><td style="text-align: left;"> Cir. 204, </td><td style="width: 20px;"><br></td><td style="text-align: left;"> U.S.F.S.: </td><td style="width: 20px;"><br></td><td style="text-align: left;"> Strength tests of cross-arms. </td></tr> +</tbody> +</table> +</center> + +<a name="pg125"></a> + +<a name="III_23"></a> +<h4><i>Other Tests</i></h4> + +<p>Many other kinds of tests are made as occasion demands. One kind +consists of barrels and liquid containers, match-boxes, and +explosive containers. These articles are subjected to shocks +such as they would receive in transit and in handling, and also +to hydraulic pressure.</p> + +<p>One of the most important tests from a practical standpoint is +that of built-up structures such as compounded beams composed of +small pieces bolted together, mortised joints, wooden trusses, +etc. Tests of this kind can best be worked out according to the +specific requirements in each case.</p> + +<a name="pg126"></a><br> +<a name="pg127"></a> +<a name="APPENDIX"></a><h2>APPENDIX</h2> + +<a name="APPENDIX_1"></a> +<h3>SAMPLE WORKING PLAN OF THE U.S. FOREST SERVICE</h3> + +<hr> + +<h3>MECHANICAL PROPERTIES OF WOODS GROWN IN THE UNITED STATES</h3> +<h4>Working Plan No. 124</h4> + +<hr> + +<h4>PURPOSE OF WORK</h4> + +<p>It is the general purpose of the work here outlined to provide:</p> + +<p>(<i>a</i>) Reliable data for comparing the mechanical properties of +various species;</p> + +<p>(<i>b</i>) Data for the establishment of correct strength functions +or working stresses;</p> + +<p>(<i>c</i>) Data upon which may be based analyses of the influence on +the mechanical properties of such factors as:</p> + +<p>Locality;</p> + +<p>Distance of timber from the pith of the tree;</p> + +<p>Height of timber in the tree;</p> + +<p>Change from the green to the air-dried condition, etc.</p> + +<p>The mechanical properties which will be considered and the +principal tests used to determine them are as follows:</p> + +<p>Strength and stiffness—</p> +<p class="ind">Static bending;</p> +<p class="ind">Compression parallel to grain;</p> +<p class="ind">Compression perpendicular to grain;</p> +<p class="ind">Shear.</p> + +<p>Toughness—</p> +<p class="ind">Impact bending;</p> +<p class="ind">Static bending;</p> +<p class="ind">Work to maximum load and total work.</p> + +<a name="pg128"></a> + +<p>Cleavability—</p> +<p class="ind">Cleavage test.</p> + +<p>Hardness— +<p class="ind">Modification of Janka ball test for surface hardness.</p> + +<h4>MATERIAL</h4> + +<h5><i>Selection and Number of Trees</i></h5> + +<p>The material will be from trees selected in the forest by one +qualified to determine the species. From each locality, three to +five dominant trees of merchantable size and approximately +average age will be so chosen as to be representative of the +dominant trees of the species. Each species will eventually be +represented by trees from five to ten localities. These +localities will be so chosen as to be representative of the +commercial range of the species. Trees from one to three +localities will be used to represent each species until most of +the important species have been tested.</p> + +<p>The 16-foot butt log will be taken from each tree selected and +the entire merchantable hole of one average tree for each +species.</p> + +<h5><i>Field Notes and Shipping Instructions</i></h5> + +<p>Field notes as outlined in Form—<i>a</i> Shipment Description, +Manual of the Branch of Products, will be fully and carefully +made by the collector. The age of each tree selected will be +recorded and any other information likely to be of interest or +importance will also be made a part of these field notes. Each +log will have the bark left on. It will be plainly marked in +accordance with directions given under Detailed Instructions. +All material will be shipped to the laboratory immediately after +being cut. No trees will be cut until the collector is notified +that the laboratory is ready to receive the material.</p> + +<h4>DETAILED INSTRUCTIONS</h4> + +<h5><i>Part of Tree to be Tested</i></h5> + +<p>(<i>a</i>) For determining the value of tree and locality and the +influence on the mechanical properties of distance from the +pith, a 4-foot bolt will be cut from the top end of each 16-foot +butt log.</p> + +<a name="pg129"></a> + +<p>(<i>b</i>) For investigating the variation of properties with the +height of timber in the tree, all the logs from one average tree +will be used.</p> + +<p>(<i>c</i>) For investigating the effect of drying the wood, the bolt +next below that provided for in (<i>a</i>) will be used in the case +of one tree from each locality.</p> + +<h5><i>Marking and Grouping of Material</i></h5> + +<p>The marking will be standard except as noted. Each log will be +considered a "piece." The piece numbers will be plainly marked +upon the butt end of each log by the collector. The north side +of each log will also be marked.</p> + +<p>When only one bolt from a tree is used it will be designated by +the number of the log from which it is cut. Whenever more than +one bolt is taken from a tree, each 4-foot bolt or length of +trunk will be given a letter (mark), <i>a, b, c,</i> etc., beginning +at the stump.</p> + +<p>All bolts will be sawed into 2-1/2" × 2-1/2" sticks and the +sticks marked according to the sketch, <a href="#fig50">Fig. 50</a>. The letters <i>N, +E, S,</i> and <i>W</i> indicate the cardinal points when known; when +these are unknown, <i>H, K, L,</i> and <i>M</i> will be used. Thus, <i>N5, +K8, S7, M4</i> are stick numbers, the letter being a part of the +stick number.</p> + +<p class="ctr"><img src="images/fig50.jpg" alt="Figure 50" id="fig50" /></p> +<p class="imgtitle">Figure 50</p> +<p class="imgtext"> Method of cutting and marking test +specimens.</p> + +<p>Only straight-grained specimens, free from defects which will +affect their strength, will be tested.</p> + +<h5><i>Care of Material</i></h5> + +<p>No material will be kept in the bolt or log long enough to be +damaged or disfigured by checks, rot, or stains.</p> + +<a name="pg130"></a> + +<p><i>Green material</i>: The material to be tested green will be kept +in a green state by being submerged in water until near the time +of test. It will then be surfaced, sawed to length, and stored +in damp sawdust at a temperature of 70°F. (as nearly as +practicable) until time of test. Care should be taken to avoid +as much as possible the storage of green material in any form.</p> + +<p><i>Air-dry material</i>: The material to be air-dried will be cut +into sticks 2-1/2" × 2-1/2" × 4'. The ends of these sticks will +be paraffined to prevent checking. This material will be so +piled as to leave an air space of at least one-half inch on each +side of each stick, and in such a place that it will be +protected from sunshine, rain, snow, and moisture from the +ground. The sticks will be surfaced and cut to length just +previous to test.</p> + +<h5><i>Order of Tests</i></h5> + +<p>The order of tests in all cases will be such as to eliminate so +far as possible from the comparisons the effect of changes of +condition of the specimens due to such factors as storage and +weather conditions.</p> + +<p>The material used for determining the effect of height in tree +will be tested in such order that the average time elapsing from +time of cutting to time of test will be approximately the same +for all bolts from any one tree. + +<h5><i>Tests on Green Material</i></h5> + +<p>The tests on all bolts, except those from which a comparison of +green and dry timber is to be gotten, will be as follows:</p> + +<p><i>Static bending</i>: One stick from each pair. A pair consists of +two adjacent sticks equidistant from the pith, as <i>N</i>7 and <i>N</i>8, +or <i>H</i>5 and <i>H</i>6.</p> + +<p><i>Impact bending</i>: Four sticks; one to be taken from near the +pith; one from near the periphery; and two representative of the +cross section.</p> + +<p><i>Compression parallel to grain</i>: One specimen from each stick. +These will be marked "1" in addition to the number of the stick +from which they are taken.</p> + +<p><i>Compression perpendicular to grain</i>: One specimen from each of +50 per cent of the static bending sticks. These will be marked +<a name="pg131"></a> +"2" in addition to the number of the stick from which they are +cut.</p> + +<p><i>Hardness</i>: One specimen from each of the other 50 per cent of +the static bending sticks. These specimens will be marked "4."</p> + +<p><i>Shear</i>: Six specimens from sticks not tested in bending or from +the ends cut off in preparing the bending specimens. Two +specimens will be taken from near the pith; two from near the +periphery; and two that are representative of the average +growth. One of each two will be tested in radial shear and the +other in tangential shear. These specimens will have the mark +"3."</p> + +<p><i>Cleavage</i>: Six specimens chosen and divided just as those for +shearing. These specimens will have the mark "5." (For sketches +showing radial and tangential cleavage, <a href="#fig45">see Fig. 45</a>.)</p> + +<p>When it is impossible to secure clear specimens for all of the +above tests, tests will have precedence in the order in which +they are named.</p> + +<h5><i>Tests to Determine the Effect of Air-drying</i></h5> + +<p>These tests will be made on material from the adjacent bolts +mentioned in "<i>c</i>" under Part of Tree to be Tested. Both bolts +will be cut as outlined above. One-half the sticks from each +bolt will be tested green, the other half will be air-dried and +tested. The division of green and air-dry will be according to +the following scheme:</p> + +<center> +<table summary="text"> +<tbody> +<tr><td colspan="14"> STICK NUMBERS</td></tr> +<tr><td> Lower bolt, </td><td> 1, </td><td><br></td><td><br></td><td> 4, </td><td> 5, </td><td><br></td><td><br></td><td> 8, </td><td> 9, </td><td><br></td><td rowspan="2" colspan="1"> etc. </td><td rowspan="2" colspan="1"><big><big><big><big>}</big></big></big></big></td><td rowspan="2" colspan="1"> Tested green </td></tr> +<tr><td> Upper bolt, </td><td><br></td><td> 2, </td><td> 3, </td><td><br></td><td><br></td><td> 6, </td><td> 7, </td><td><br></td><td><br></td><td> 10, </td></tr> +<tr><td> Lower bolt, </td><td><br></td><td> 2, </td><td> 3, </td><td><br></td><td><br></td><td> 6, </td><td> 7, </td><td><br></td><td><br></td><td> 10, </td><td rowspan="2" colspan="1"> etc. </td><td rowspan="2" colspan="1"> <big><big><big><big>}</big></big></big></big></td><td rowspan="2" colspan="1"> Air-dried and tested </td></tr> +<tr><td> Upper bolt, </td><td> 1, </td><td><br></td><td><br></td><td> 4, </td><td> 5, </td><td><br></td><td><br></td><td> 8, </td><td> 9, </td><td><br></td></tr> +</tbody> +</table> +</center> + +<p>All green sticks from these two bolts will be tested as if they +were from the same bolt and according to the plan previously +outlined for green material from single bolts. The tests on the +air-dried material will be the same as on the green except for +the difference of seasoning.</p> + +<a name="pg132"></a> + +<p>The material will be tested at as near 12 per cent moisture as +is practicable. The approximate weight of the air-dried +specimens at 12 per cent moisture will be determined by +measuring while green 20 per cent of the sticks to be air-dried +and assuming their dry gravity to be the same as that of the +specimens tested green. This 20 per cent will be weighed as +often as is necessary to determine the proper time of test.</p> + +<h5><i>Methods of Test</i></h5> + +<p>All tests will be made according to Circular 38 except in case +of conflict with the instructions given below:</p> + +<p><i>Static bending</i>: The tests will be on specimens 2" × 2" × 30" +on 28-inch span. Load will be applied at the centre.</p> + +<p>In all tests the load-deflection curve will be carried to or +beyond the maximum load. In one-third of the tests the +load-deflection curve will be continued to 6-inch deflection, or +till the specimen fails to support a 200-pound load. Deflection +readings for equal increments of load will be taken until well +past the elastic limit, after which the scale beam will be kept +balanced and the load read for each 0.1-inch deflection. The +load and deflection at first failure, maximum load and points of +sudden change, will be shown on the curve sheet even if they do +not occur at one of the regular load or deflection increments.</p> + +<p><i>Impact bending</i>: The impact bending tests will be on specimens +of the same size as those used in static bending. The span will +be 28 inches.</p> + +<p>The tests will be by increment drop. The first drop will be 1 +inch and the increase will be by increments of 1 inch till a +height of 10 inches is reached, after which increments of 2 +inches will be used until complete failure occurs or 6-inch +deflection is secured.</p> + +<p>A 50-pound hammer will be used when with drops up to 68 inches +it is practically certain that it will produce complete failure +or 6-inch deflection in the case of all specimens of a species. +For all other species, a 100-pound hammer will be used.</p> + +<p>In all cases drum records will be made until first failure. Also +the height of drop causing complete failure or 6-inch deflection +will be noted.</p> + +<p><i>Compression parallel to grain</i>: This test will be on specimens +<a name="pg133"></a> +2" × 2" × 8" in size. On 20 per cent of these tests +load-compression curves for a 6-inch centrally located gauge +length will be taken. Readings will be continued until the +elastic limit is well passed. The other 80 per cent of the tests +will be made for the purpose of obtaining the maximum load only.</p> + +<p><i>Compression perpendicular to grain</i>: This test will be on +specimens 2" × 2" × 6" in size. The bearing plates will be 2 +inches wide. The rate of descent of the moving head will be +0.024 inch per minute. The load-compression curve will be +plotted to 0.1 inch compression and the test will then be +discontinued.</p> + +<p><i>Hardness</i>: The tool shown in <a href="#fig43">Fig. 43</a> (an adaptation of the +apparatus used by the German investigator, Janka) will be used. +The rate of descent of the moving head will be 0.25 inch per +minute. When the penetration has progressed to the point at +which the plate "<i>a</i>" becomes tight, due to being pressed +against the wood, the load will be read and recorded.</p> + +<p>Two penetrations will be made on a tangential surface, two on a +radial, and one on each end of each specimen tested. The choice +between the two radial and between the two tangential surfaces +and the distribution of the penetrations over the surfaces will +be so made as to get a fair average of heart and sap, slow and +fast growth, and spring and summer wood. Specimens will be 2" × +2" × 6".</p> + +<p><i>Shear</i>: The tests will be made with a tool slightly modified +from that shown in Circular 38. The speed of descent of head +will be 0.015 inch per minute. The only measurements to be made +are those of the shearing area. The offset will be 1/8 inch. +Specimens will be 2" × 2" × 2-1/2" in size. (For definition of +offset and form of test specimen, <a href="#fig38">see Fig. 38</a>.)</p> + +<p><i>Cleavage</i>: The cleavage tests will be made on specimens of the +form and size shown in <a href="#fig45">Fig. 45</a>. The apparatus will be as shown +in Fig. 44. The maximum load only will be taken and the result +expressed in pounds per inch of width. The speed of the moving +head will be 0.25 inch per minute.</p> + +<h5><i>Moisture Determinations</i></h5> + +<p>Moisture determinations will be made on all specimens tested +except those to be photographed or kept for exhibit. A 1-inch +<a name="pg134"></a> +disk will be cut from near the point of failure of bending and +compression parallel specimens, from the portion under the plate +in the case of the compression perpendicular specimens, and from +the centre of the hardness test specimens. The beads from the +shear specimens will be used as moisture disks. In the case of +the cleavage specimens a piece 1/2 inch thick will be split off +parallel to the failure and used as a moisture disk.</p> + +<h4>RECORDS</h4> + +<p>All records will be standard.</p> + +<h4>PHOTOGRAPHS</h4> + +<h5><i>Cross Sections</i></h5> + +<p>Just before cutting into sticks, the freshly cut end of at least +one bolt from each tree will be photographed. A scale of inches +will be shown in this photograph.</p> + +<h5><i>Specimens</i></h5> + +<p>Three photographs will be made of a group consisting of four 2" + × 2" × 30" specimens chosen from the material from each +locality. Two of these specimens will be representative of +average growth, one of fast and one of slow growth. These +photographs will show radial, tangential, and end surfaces for +each specimen.</p> + +<h5><i>Failures</i></h5> + +<p>Typical and abnormal failures of material from each site will be +photographed.</p> + +<h5><i>Disposition of Material</i></h5> + +<p>The specimens photographed to show typical and abnormal failures +will be saved for purposes of exhibit until deemed by the person +in charge of the laboratory to be of no further value.</p> + +<a name="pg135"></a> + +<h3>SHRINKAGE AND SPECIFIC GRAVITY</h3> + +<h4>Appendix to Working Plan 124</h4> + +<hr> + +<h4>PURPOSE OF WORK</h4> + +<p>It is the purpose of this work to secure data on the shrinkage +and specific gravity of woods tested under Project 124. The +figures to be obtained are for use as average working values +rather than as the basis for a detailed study of the principles +involved.</p> + +<h4>MATERIAL</h4> + +<p>The material will be taken from that provided for mechanical +tests.</p> + +<h4>RADIAL AND TANGENTIAL SHRINKAGE</h4> + +<h5><i>Specimens</i></h5> + +<p><i>Preparation</i>: Two specimens 1 inch thick, 4 inches wide, and 1 +inch long will be obtained from near the periphery of each "<i>d</i>" +bolt. These will be cut from the sector-shaped sections left +after securing the material for the mechanical tests or from +disks cut from near the end of the bolt. They will be taken from +adjoining pieces chosen so that the results will be comparable +for use in determining radial and tangential shrinkage. (When a +disk is used, care must be taken that it is green and has not +been affected by the shrinkage and checking near the end of the +bolt.)</p> + +<p>One of these specimens will be cut with its width in the radial +direction and will be used for the determination of radial +shrinkage. The other will have its width in the tangential +direction and will be used for tangential shrinkage. These +specimens will not be surfaced.</p> + +<p><i>Marking</i>: The shrinkage specimens will retain the shipment and +piece numbers and marks of the bolts from which they are taken, +and will have the additional mark <i>7</i>R or <i>7</i>T according as +their widths are in the radial or tangential direction.</p> + +<a name="pg136"></a> + +<p><i>Shrinkage measurements</i>: The shrinkage specimens will be +carefully weighed and measured soon after cutting. Rings per +inch, per cent sap, and per cent summer wood will be measured. +They will then be air-dried in the laboratory to constant +weight, and afterward oven-dried at 100°C. (212°F.), when they +will again be weighed and measured.</p> + +<h4>VOLUMETRIC SHRINKAGE AND SPECIFIC GRAVITY</h4> + +<h5><i>Specimens</i></h5> + +<p><i>Selection and preparation</i>: Four 2" × 2" × 6" specimens will be +cut from the mechanical test sticks of each "<i>d</i>" bolt; also +from each of the composite bolts used in getting a comparison of +green and air-dry. One of these specimens will be taken from +near the pith and one from near the periphery; the other two +will be representative of the average growth of the bolt. The +sides of these specimens will be surfaced and the ends smooth +sawn.</p> + +<p><i>Marking</i>: Each specimen will retain the shipment, piece, and +stick numbers and mark of the stick from which it is cut, and +will have the additional mark "<i>S</i>."</p> + +<p><i>Manipulation</i>: Soon after cutting, each specimen will be +weighed and its volume will be determined by the method +described below. The rings per inch and per cent summer wood, +where possible, will be determined, and a carbon impression of +the end of the specimen made. It will then be air-dried in the +laboratory to a constant weight and afterward oven-dried at +100°C. When dry, the specimen will be taken from the oven, +weighed, and a carbon impression of its end made. While still +warm the specimen will be dipped in hot paraffine. The volume +will then be determined by the following method:</p> + +<p>On one pan of a pair of balances is placed a container having in +it water enough for the complete submersion of the test +specimen. This container and water is balanced by weights placed +on the other scale pan. The specimen is then held completely +submerged and not touching the container while the scales are +again balanced. The weight required to balance is the weight of +water displaced by the specimen, and hence if in grams is +numerically equal to the volume of the specimen in cubic +centimetres. <a name="pg137"></a> A diagrammatic sketch of the arrangement of this +apparatus is shown in <a href="#fig51">Fig. 51</a>.</p> + +<p class="ctr"><img src="images/fig51.jpg" alt="Figure 51" id="fig51" /></p> +<p class="imgtitle">Figure 51</p> +<p class="imgtext"> Diagram of specific gravity apparatus, +showing a balance with container (<i>c</i>) filled with water in +which the test block (<i>b</i>) is held submerged by a light rod +(<i>a</i>) which is adjustable vertically and provided with a sharp +point to be driven into the specimen.</p> + +<p>Air-dry specimens will be dipped in water and then wiped dry +after the first weighing and just before being immersed for +weighing their displacement. All displacement determinations +will be made as quickly as possible in order to minimize the +absorption of water by the specimen.</p> + +<a name="pg138"></a> +<a name="APPENDIX_2"></a> +<h3>STRENGTH VALUES FOR STRUCTURAL TIMBERS</h3> + +<h4>(From Cir. 189, U.S. Forest Service)</h4> + +<p>The following tables bring together in condensed form the +average strength values resulting from a large number of tests +made by the Forest Service on the principal structural timbers +of the United States. These results are more completely +discussed in other publications of the Service, a list of which +is given on <a href="#pg157">pages 157</a>-159.</p> + +<p>The tests were made at the laboratories of the U.S. Forest +Service, in cooperation with the following institutions: Yale +Forest School, Purdue University, University of California, +University of Oregon, University of Washington, University of +Colorado, and University of Wisconsin.</p> + +<p>Tables <a href="#TABLE_18">XVIII</a> and <a href="#TABLE_19">XIX</a> give the average results obtained from +tests on green material, while Tables <a href="#TABLE_20">XX</a> and <a href="#TABLE_21">XXI</a> give average +results from tests on air-seasoned material. The small +specimens, which were invariably 2" × 2" in cross section, were +free from defects such as knots, checks, and cross grain; all +other specimens were representative of material secured in the +open market. The relation of stresses developed in different +structural forms to those developed in the small clear specimens +is shown for each factor in the column headed "Ratio to 2" × +2"." Tests to determine the mechanical properties of different +species are often confined to small, clear specimens. The ratios +included in the tables may be applied to such results in order +to approximate the strength of the species in structural sizes, +and containing the defects usually encountered, when tests on +such forms are not available.</p> + +<p>A comparison of the results of tests on seasoned material with +those from tests on green material shows that, without +exception, the strength of the 2" × 2" specimens is increased by +lowering the moisture content, but that increase in strength of +other sizes is much more erratic. Some specimens, in fact, show +an apparent loss in strength due to seasoning. If structural +timbers are <a name="pg139"></a> seasoned slowly, in order to avoid excessive +checking, there should be an increase in their strength. In the +light of these facts it is not safe to base working stresses on +results secured from any but green material. For a discussion of +factors of safety and safe working stresses for structural +timbers see the Manual of the American Railway Engineering +Association, Chicago, 1911. A table from that publication, +giving working unit stresses for structural timber, is +reproduced in this book, <a href="#TABLE_22">see Table XXII</a>.</p> + +<a name="pg140"></a> + +<center> +<table id="TABLE_18" summary="TABLE_XVIII" border="3" cellspacing="0" cellpadding="1" width="100%"> +<tbody> +<tr><th rowspan="1" colspan="14"> TABLE XVIII </th></tr> +<tr><th rowspan="1" colspan="14"> BENDING TESTS ON GREEN MATERIAL </th></tr> +<tr><th rowspan="3" colspan="1"> Species </th> <th rowspan="1" colspan="2"> Sizes </th> + <th rowspan="2" colspan="1"> Number of tests </th> + <th rowspan="2" colspan="1"> Per cent of moisture </th> + <th rowspan="2" colspan="1"> Rings per inch </th> + <th rowspan="1" colspan="2"> F.S. at E.L. </th> + <th rowspan="1" colspan="2"> M. of R. </th> + <th rowspan="1" colspan="2"> M. of E. </th> + <th rowspan="1" colspan="2"> Calculated shear </th></tr> +<tr> <th> Cross Section </th> + <th> Span </th> + <th> Average per sq. inch </th> + <th> Ratio to 2" by 2" </th> + <th> Average per sq. inch</th> + <th>Ratio to 2" by 2" </th> + <th> Average per sq. inch </th> + <th>Ratio to 2" by 2" </th> + <th> Average per sq. inch </th> + <th>Ratio to 2" by 2" </th></tr> +<tr> <th><i>Inches</i></th> + <th><i>Ins.</i></th> + <th><br></th> <th><br></th> <th><br></th> <th><i>Lbs.</i></th> + <th><br></th> <th><i>Lbs.</i></th> + <th><br></th> <th>1,000 <i>lbs.</i></th> + <th><br></th> <th><i>Lbs.</i></th> + <th><br></th></tr> +<tr><td style="text-align: left;"> Longleaf pine </td> <td> 12 by 12 </td><td> 138 </td><td> 4 </td> <td> 28.6 </td><td> 9.7 </td> <td> 4,029 </td><td> 0.83 </td><td> 6,710 </td><td> 0.74 </td><td> 1,523 </td><td> 0.99 </td><td> 261 </td><td> 0.86 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 10 by 16 </td><td> 168 </td><td> 4 </td> <td> 26.8 </td><td> 16.7 </td><td> 6,453 </td><td> .85 </td> <td> 6,453 </td><td> .71 </td> <td> 1,626 </td><td> 1.05 </td><td> 306 </td><td> 1.01 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 8 by 16 </td> <td> 156 </td><td> 7 </td> <td> 28.4 </td><td> 14.6 </td><td> 3,147 </td><td> .64 </td> <td> 5,439 </td><td> .60 </td> <td> 1,368 </td><td> .89 </td ><td> 390 </td><td> 1.29 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 6 by 16 </td> <td> 132 </td><td> 1 </td> <td> 40.3 </td><td> 21.8 </td><td> 4,120 </td><td> .83 </td> <td> 6,460 </td><td> .71 </td> <td> 1,190 </td><td> .77 </td> <td> 378 </td><td> 1.25 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 6 by 10 </td> <td> 180 </td><td> 1 </td> <td> 31.0 </td><td> 6.2 </td> <td> 3,580 </td><td> .72 </td> <td> 6,500 </td><td> .72 </td> <td> 1,412 </td><td> .92 </td> <td> 175 </td><td> .58 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 6 by 8 </td> <td> 180 </td><td> 2 </td> <td> 27.0 </td><td> 8.2 </td> <td> 3,735 </td><td> .75 </td> <td> 5,745 </td><td> .63 </td> <td> 1,282 </td><td> .83 </td> <td> 121 </td><td> .40 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 30 </td> <td> 15 </td> <td> 33.9 </td><td> 14.1 </td><td> 4,950 </td><td> 1.00 </td><td> 9,070 </td><td> 1.00 </td><td> 1,540 </td><td> 1:00 </td><td> 303 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Douglas fir </td> <td> 8 by 16 </td> <td> 180 </td><td> 191 </td><td> 31.5 </td><td> 11.0 </td><td> 3,968 </td><td> .76 </td> <td> 5,983 </td><td> .72 </td> <td> 1,517 </td><td> .95 </td> <td> 269 </td><td> .81 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 5 by 8 </td> <td> 180 </td><td> 84 </td> <td> 30.1 </td><td> 10.8 </td><td> 3,693 </td><td> .71 </td> <td> 5,178 </td><td> .63 </td> <td> 1,533 </td><td> .96 </td> <td> 172 </td><td> .52 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 12 </td> <td> 180 </td><td> 27 </td> <td> 35.7 </td><td> 20.3 </td><td> 3,721 </td><td> .71 </td> <td> 5,276 </td><td> .64 </td> <td> 1,642 </td><td> 1.03 </td><td> 256 </td><td> .77 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 10 </td> <td> 180 </td><td> 26 </td> <td> 32.9 </td><td> 21.6 </td><td> 3,160 </td><td> .60 </td> <td> 4,699 </td><td> .57 </td> <td> 1,593 </td><td> 1.00 </td><td> 189 </td><td> .57 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 8 </td> <td> 180 </td><td> 29 </td> <td> 33.6 </td><td> 17.6 </td><td> 3,593 </td><td> .69 </td> <td> 5,352 </td><td> .65 </td> <td> 1,607 </td><td> 1.01 </td><td> 171 </td><td> .51 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 24 </td> <td> 568 </td><td> 30.4 </td><td> 11.6 </td><td> 5,227 </td><td> 1.00 </td><td> 9,070 </td><td> 1.00 </td><td> 1,540 </td><td> 1.00 </td><td> 303 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Douglas fir (fire-killed) </td><td> 8 by 16 </td> <td> 180 </td><td> 30 </td> <td> 36.8 </td><td> 10.9 </td><td> 3,503 </td><td> .80 </td> <td> 4,994 </td><td> .64 </td> <td> 1,531 </td><td> .94 </td> <td> 330 </td><td> 1.19 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 12 </td> <td> 180 </td><td> 32 </td> <td> 34.2 </td><td> 17.7 </td><td> 3,489 </td><td> .80 </td> <td> 5,085 </td><td> .66 </td> <td> 1,624 </td><td> .99 </td> <td> 247 </td><td> .89 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 10 </td> <td> 180 </td><td> 32 </td> <td> 38.9 </td><td> 18.1 </td><td> 3,851 </td><td> .88 </td> <td> 5,359 </td><td> .69 </td> <td> 1,716 </td><td> 1.05 </td><td> 216 </td><td> .78 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 8 </td> <td> 180 </td><td> 31 </td> <td> 37.0 </td><td> 15.7 </td><td> 3,403 </td><td> .78 </td> <td> 5,305 </td><td> .68 </td> <td> 1,676 </td><td> 1.02 </td><td> 169 </td><td> .61 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 30 </td> <td> 290 </td><td> 33.2 </td><td> 17.2 </td><td> 4,360 </td><td> 1.00 </td><td> 7,752 </td><td> 1.00 </td><td> 1,636 </td><td> 1.00 </td><td> 277 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Shortleaf pine </td> <td> 8 by 16 </td> <td> 180 </td><td> 12 </td> <td> 39.5 </td><td> 12.1 </td><td> 3,185 </td><td> .73 </td> <td> 5,407 </td><td> .70 </td> <td> 1,438 </td><td> 1.03 </td><td> 362 </td><td> 1.40 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 8 by 14 </td> <td> 180 </td><td> 12 </td> <td> 45.8 </td><td> 12.7 </td><td> 3,234 </td><td> .74 </td> <td> 5,781 </td><td> .75 </td> <td> 1,494 </td><td> 1.07 </td><td> 338 </td><td> 1.31 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 8 by 12 </td> <td> 180 </td><td> 24 </td> <td> 52.2 </td><td> 11.8 </td><td> 3,265 </td><td> .75 </td> <td> 5,503 </td><td> .71 </td> <td> 1,480 </td><td> 1.06 </td><td> 277 </td><td> 1.07 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 5 by 8 </td> <td> 180 </td><td> 24 </td> <td> 47.8 </td><td> 11.5 </td><td> 3,519 </td><td> .81 </td> <td> 5,732 </td><td> .74 </td> <td> 1,485 </td><td> 1.06 </td><td> 185 </td><td> .72 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 30 </td> <td> 254 </td><td> 51.7 </td><td> 13.6 </td><td> 4,350 </td><td> 1.00 </td><td> 7,710 </td><td> 1.00 </td><td> 1,395 </td><td> 1.00 </td><td> 258 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Western larch </td> <td> 8 by 16 </td> <td> 180 </td><td> 32 </td> <td> 51.0 </td><td> 25.3 </td><td> 3,276 </td><td> .77 </td> <td> 4,632 </td><td> .64 </td> <td> 1,272 </td><td> .97 </td> <td> 298 </td><td> 1.11 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 8 by 12 </td> <td> 180 </td><td> 30 </td> <td> 50.3 </td><td> 23.2 </td><td> 3,376 </td><td> .79 </td> <td> 5,286 </td><td> .73 </td> <td> 1,331 </td><td> 1.02 </td><td> 254 </td><td> .94 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 5 by 8 </td> <td> 180 </td><td> 14 </td> <td> 56.0 </td><td> 25.6 </td><td> 3,528 </td><td> .83 </td> <td> 5,331 </td><td> .74 </td> <td> 1,432 </td><td> 1.09 </td><td> 169 </td><td> .63 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 28 </td> <td> 189 </td><td> 46.2 </td><td> 26.2 </td><td> 4,274 </td><td> 1.00 </td><td> 7,251 </td><td> 1.00 </td><td> 1,310 </td><td> 1.00 </td><td> 269 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Loblolly pine </td> <td> 8 by 16 </td> <td> 180 </td><td> 17 </td> <td> 15.8 </td><td> 6.1 </td> <td> 3,094 </td><td> .75 </td> <td> 5,394 </td><td> .69 </td> <td> 1,406 </td><td> .98 </td> <td> 383 </td><td> 1.44 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 5 by 12 </td> <td> 180 </td><td> 94 </td> <td> 60.9 </td><td> 5.9 </td> <td> 3,030 </td><td> .74 </td> <td> 5,028 </td><td> .64 </td> <td> 1,383 </td><td> .96 </td> <td> 221 </td><td> .83 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 30 </td> <td> 44 </td> <td> 70.9 </td><td> 5.4 </td> <td> 4,100 </td><td> 1.00 </td><td> 7,870 </td><td> 1.00 </td><td> 1,440 </td><td> 1.00 </td><td> 265 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Tamarack </td> <td> 6 by 12 </td> <td> 162 </td><td> 15 </td> <td> 57.6 </td><td> 16.6 </td><td> 2,914 </td><td> .75 </td> <td> 4,500 </td><td> .66 </td> <td> 1,202 </td><td> 1.05 </td><td> 255 </td><td> 1.11 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 10 </td> <td> 162 </td><td> 15 </td> <td> 43.5 </td><td> 11.4 </td><td> 2,712 </td><td> .70 </td> <td> 4,611 </td><td> .68 </td> <td> 1,238 </td><td> 1.08 </td><td> 209 </td><td> .91 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 30 </td> <td> 82 </td> <td> 38.8 </td><td> 14.0 </td><td> 3,875 </td><td> 1.00 </td><td> 6,820 </td><td> 1.00 </td><td> 1,141 </td><td> 1.00 </td><td> 229 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Western hemlock </td> <td> 8 by 16 </td> <td> 180 </td><td> 39 </td> <td> 42.5 </td><td> 15.6 </td><td> 3,516 </td><td> .80 </td> <td> 5,296 </td><td> .73 </td> <td> 1,445 </td><td> 1.01 </td><td> 261 </td><td> .92 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 28 </td> <td> 52 </td> <td> 51.8 </td><td> 12.1 </td><td> 4.406 </td><td> 1.00 </td><td> 7,294 </td><td> 1.00 </td><td> 1,428 </td><td> 1.00 </td><td> 284 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Redwood </td> <td> 8 by 16 </td> <td> 180 </td><td> 14 </td> <td> 86.5 </td><td> 19.9 </td><td> 3,734 </td><td> .79 </td> <td> 4,492 </td><td> .64 </td> <td> 1,016 </td><td> .96 </td> <td> 300 </td><td> 1.21 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 6 by 12 </td> <td> 180 </td><td> 14 </td> <td> 87.3 </td><td> 17.8 </td><td> 3,787 </td><td> .80 </td> <td> 4,451 </td><td> .64 </td> <td> 1,068 </td><td> 1.00 </td><td> 224 </td><td> .90 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 7 by 9 </td> <td> 180 </td><td> 14 </td> <td> 79.8 </td><td> 16.7 </td><td> 4,412 </td><td> .93 </td> <td> 5,279 </td><td> .76 </td> <td> 1,324 </td><td> 1.25 </td><td> 199 </td><td> .80 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 3 by 14 </td> <td> 180 </td><td> 13 </td> <td> 86.1 </td><td> 23.7 </td><td> 3,506 </td><td> .74 </td> <td> 4,364 </td><td> .62 </td> <td> 947 </td> <td> .89 </td> <td> 255 </td><td> 1.03 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 12 </td> <td> 180 </td><td> 12 </td> <td> 70.9 </td><td> 18.6 </td><td> 3,100 </td><td> .65 </td> <td> 3,753 </td><td> .54 </td> <td> 1,052 </td><td> .99 </td> <td> 187 </td><td> .75 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 10 </td> <td> 180 </td><td> 13 </td> <td> 55.8 </td><td> 20.0 </td><td> 3,285 </td><td> .69 </td> <td> 4,079 </td><td> .58 </td> <td> 1,107 </td><td> 1.04 </td><td> 169 </td><td> .68 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 8 </td> <td> 180 </td><td> 13 </td> <td> 63.8 </td><td> 21.5 </td><td> 2,989 </td><td> .63 </td> <td> 4,063 </td><td> .58 </td> <td> 1,141 </td><td> 1.08 </td><td> 134 </td><td> .54 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 28 </td> <td> 157 </td><td> 75.5 </td><td> 19.1 </td><td> 4,750 </td><td> 1.00 </td><td> 6,980 </td><td> 1.00 </td><td> 1,061 </td><td> 1.00 </td><td> 248 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Norway pine </td> <td> 6 by 12 </td> <td> 162 </td><td> 15 </td> <td> 50.3 </td><td> 12.5 </td><td> 2,305 </td><td> .82 </td> <td> 3,572 </td><td> .69 </td> <td> 987 </td> <td> 1.03 </td><td> 201 </td><td> 1.17 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 12 </td> <td> 162 </td><td> 18 </td> <td> 47.9 </td><td> 14.7 </td><td> 2,648 </td><td> .94 </td> <td> 4,107 </td><td> .79 </td> <td> 1,255 </td><td> 1.31 </td><td> 238 </td><td> 1.38 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 10 </td> <td> 162 </td><td> 16 </td> <td> 45.7 </td><td> 13.3 </td><td> 2,674 </td><td> .95 </td> <td> 4,205 </td><td> .81 </td> <td> 1,306 </td><td> 1.36 </td><td> 198 </td><td> 1.15 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 30 </td> <td> 133 </td><td> 32.3 </td><td> 11.4 </td><td> 2,808 </td><td> 1.00 </td><td> 5,173 </td><td> 1.00 </td><td> 960 </td> <td> 1.00 </td><td> 172 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Red spruce </td> <td> 2 by 10 </td> <td> 144 </td><td> 14 </td> <td> 32.5 </td><td> 21.9 </td><td> 2,394 </td><td> .66 </td> <td> 3,566 </td><td> .60 </td> <td> 1,180 </td><td> 1.02 </td><td> 181 </td><td> .80 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 26 </td> <td> 60 </td> <td> 37.3 </td><td> 21.3 </td><td> 3,627 </td><td> 1.00 </td><td> 5,900 </td><td> 1.00 </td><td> 1,157 </td><td> 1.00 </td><td> 227 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> White spruce </td> <td> 2 by 10 </td> <td> 144 </td><td> 16 </td> <td> 40.7 </td><td> 9.3 </td> <td> 2,239 </td><td> .72 </td> <td> 3,288 </td><td> .63 </td> <td> 1,081 </td><td> 1.08 </td><td> 166 </td><td> .83 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 26 </td> <td> 83 </td> <td> 58.3 </td><td> 10.2 </td><td> 3.090 </td><td> 1.00 </td><td> 5,185 </td><td> 1.00 </td><td> 998 </td> <td> 1.00 </td><td> 199 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;" rowspan="1" colspan="14"><i>Note.—Following is an + explanation of the abbreviations used in the foregoing tables:</i><br> + F.S. at E.L. = Fiber stress at elastic limit.<br> + M. of E. = Modulus of elasticity.<br> + M. of R. = Modulus of rupture.<br> + Cr. str. at E.L. = Crushing strength at elastic limit.<br> + Cr. str. at max. ld. = Crushing strength at maximum load. </td></tr> +</tbody> +</table> +</center> + +<a name="pg141"></a> + +<center> +<table id="TABLE_19" summary="TABLE_XIX" border="3" cellspacing="0" cellpadding="1" width="100%"> +<tbody> +<tr><th rowspan="1" colspan="15"> TABLE XIX </th></tr> +<tr><th rowspan="1" colspan="15"> COMPRESSION AND SHEAR TESTS ON GREEN MATERIAL </th></tr> +<tr><th rowspan="3" colspan="1"> Species </th> <th rowspan="1" colspan="6"> Compression parallel to grain </th> + <th rowspan="1" colspan="5"> Compression perpendicular to grain </th> + <th rowspan="1" colspan="3"> Shear </th></tr> +<tr> <th> Size of specimen </th> + <th> No. of tests </th> + <th> Per cent of moisture </th> + <th> Cr. str. at E. L. per square inch </th> + <th> M. of E. per square inch </th> + <th> Cr. str. at max. ld., per square inch </th> + <th> Stress area </th> + <th> Height </th> + <th> No. of tests </th> + <th> Per cent of moisture </th> + <th>Cr. str. at max. ld., per square inch </th> + <th> No. of tests </th> + <th> Per cent of moisture </th> + <th> Shear strength per square inch </th></tr> +<tr> <th><i>Inches</i></th> + <th><br></th> <th><br></th> <th><i>Lbs.</i></th> + <th>1,000 <i>lbs.</i></th> + <th><i>Lbs.</i></th> + <th><i>Inches</i></th> + <th><i>Inches</i></th> + <th><br></th> <th><br></th> <th><i>Lbs.</i></th> + <th><br></th> <th><br></th> <th><i>Lbs.</i></th></tr> +<tr><td style="text-align: left;"> Longleaf pine </td> <td> 4 by 4 </td><td> 46 </td> <td> 26.3 </td><td> 3,480 </td><td><br></td> <td> 4,800 </td><td> 4 by 4 </td><td> 4 </td> <td> 22 </td> <td> 25.3 </td><td> 568 </td><td> 44 </td> <td> 21.8 </td><td> 973 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 14 </td> <td> 34.7 </td><td><br></td> <td><br></td> <td> 4,400 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Douglas fir </td> <td> 6 by 6 </td><td> 515 </td><td> 30.7 </td><td> 2,780 </td><td> 1,181 </td><td> 3,500 </td><td> 4 by 8 </td><td> 16 </td><td> 259 </td><td> 30.3 </td><td> 570 </td><td> 531 </td><td> 29.7 </td><td> 765 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 5 by 6 </td><td> 170 </td><td> 30.9 </td><td> 2,720 </td><td> 2,123 </td><td> 3,490 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 902 </td><td> 29.8 </td><td> 3,500 </td><td> 1,925 </td><td> 4,030 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Douglas fir (fire-killed) </td><td> 6 by 6 </td><td> 108 </td><td> 34.8 </td><td> 2,620 </td><td> 1,801 </td><td> 3,290 </td><td> 6 by 8 </td><td> 16 </td><td> 24 </td> <td> 33.7 </td><td> 368 </td><td> 77 </td> <td> 35.8 </td><td> 631 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 204 </td><td> 37.9 </td><td><br></td> <td><br></td> <td> 3,430 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Shortleaf pine </td> <td> 6 by 6 </td><td> 95 </td> <td> 41.2 </td><td> 2,514 </td><td> 1,565 </td><td> 3,436 </td><td> 5 by 8 </td><td> 16 </td><td> 12 </td> <td> 37.7 </td><td> 361 </td><td> 179 </td><td> 47.0 </td><td> 704 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 5 by 8 </td><td> 23 </td> <td> 43.5 </td><td> 2,241 </td><td> 1,529 </td><td> 3,423 </td><td> 5 by 8 </td><td> 14 </td><td> 12 </td> <td> 42.8 </td><td> 366 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 281 </td><td> 51.4 </td><td><br></td> <td><br></td> <td> 3,570 </td><td> 5 by 8 </td><td> 12 </td><td> 24 </td> <td> 53.0 </td><td> 325 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 5 by 5 </td><td> 8 </td> <td> 24 </td> <td> 47.0 </td><td> 344 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 2 by 2 </td><td> 2 </td> <td> 277 </td><td> 48.5 </td><td> 400 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Western larch </td> <td> 6 by 6 </td><td> 107 </td><td> 49.1 </td><td> 2,675 </td><td> 1,575 </td><td> 3,510 </td><td> 6 by 8 </td><td> 16 </td><td> 22 </td> <td> 43.6 </td><td> 417 </td><td> 179 </td><td> 40.7 </td><td> 700 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 491 </td><td> 50.6 </td><td> 3,026 </td><td> 1,545 </td><td> 3,696 </td><td> 6 by 8 </td><td> 12 </td><td> 20 </td> <td> 40.2 </td><td> 416 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 4 by 6 </td><td> 6 </td> <td> 53 </td> <td> 52.8 </td><td> 478 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 4 by 4 </td><td> 4 </td> <td> 30 </td> <td> 50.4 </td><td> 472 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Loblolly pine </td> <td> 8 by 8 </td><td> 14 </td> <td> 63.4 </td><td> 1,560 </td><td> 365 </td> <td> 2,140 </td><td> 8 by 4 </td><td> 8 </td> <td> 16 </td> <td> 67.2 </td><td> 392 </td><td> 121 </td><td> 83.2 </td><td> 630 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 8 </td><td> 18 </td> <td> 60.0 </td><td> 2,430 </td><td> 691 </td> <td> 3,560 </td><td> 4 by 4 </td><td> 8 </td> <td> 38 </td> <td> 44.6 </td><td> 546 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 53 </td> <td> 74.0 </td><td><br></td> <td><br></td> <td> 3,240 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Tamarack </td> <td> 6 by 7 </td><td> 4 </td> <td> 49.9 </td><td> 2,332 </td><td> 1,432 </td><td> 3,032 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td> 24 </td> <td> 39.2 </td><td> 668 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 7 </td><td> 6 </td> <td> 27.7 </td><td> 2,444 </td><td> 1,334 </td><td> 3,360 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 165 </td><td> 36.8 </td><td><br></td> <td><br></td> <td> 3,190 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Western hemlock </td> <td> 6 by 6 </td><td> 82 </td> <td> 46.6 </td><td> 2,905 </td><td> 1,617 </td><td> 3,355 </td><td> 6 by 4 </td><td> 6 </td> <td> 30 </td> <td> 48.7 </td><td> 434 </td><td> 54 </td> <td> 65.7 </td><td> 630 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 131 </td><td> 55.6 </td><td> 2,938 </td><td> 1,737 </td><td> 3,392 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Redwood </td> <td> 6 by 6 </td><td> 34 </td> <td> 83.6 </td><td> 3,194 </td><td> 1,240 </td><td> 3,882 </td><td> 6 by 8 </td><td> 16 </td><td> 13 </td> <td> 86.7 </td><td> 473 </td><td> 148 </td><td> 84.2 </td><td> 742 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 143 </td><td> 36.8 </td><td> 3,490 </td><td> 1,222 </td><td> 3,980 </td><td> 6 by 6 </td><td> 12 </td><td> 14 </td> <td> 83.0 </td><td> 424 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 6 by 7 </td><td> 9 </td> <td> 13 </td> <td> 74.7 </td><td> 477 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 6 by 3 </td><td> 14 </td><td> 13 </td> <td> 75.6 </td><td> 411 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 6 by 2 </td><td> 12 </td><td> 12 </td> <td> 66.5 </td><td> 430 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 6 by 2 </td><td> 10 </td><td> 11 </td> <td> 55.0 </td><td> 423 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 6 by 2 </td><td> 8 </td> <td> 12 </td> <td> 56.7 </td><td> 396 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 2 by 2 </td><td> 2 </td> <td> 186 </td><td> 75.5 </td><td> 569 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Norway pine </td> <td> 6 by 7 </td><td> 5 </td> <td> 29.0 </td><td> 1,928 </td><td> 905 </td> <td> 2,404 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td> 20 </td> <td> 26.7 </td><td> 589 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 7 </td><td> 8 </td> <td> 28.4 </td><td> 2,154 </td><td> 1,063 </td><td> 2,652 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 178 </td><td> 26.8 </td><td><br></td> <td><br></td> <td> 2,504 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Red spruce </td> <td> 2 by 2 </td><td> 58 </td> <td> 35.4 </td><td><br></td> <td><br></td> <td> 2,750 </td><td> 2 by 2 </td><td> 2 </td> <td> 43 </td> <td> 31.8 </td><td> 310 </td><td> 30 </td> <td> 32.0 </td><td> 758 </td></tr> +<tr><td style="text-align: left;"> White spruce </td> <td> 2 by 2 </td><td> 84 </td> <td> 61.0 </td><td><br></td> <td><br></td> <td> 2,370 </td><td> 2 by 2 </td><td> 2 </td> <td> 46 </td> <td> 50.4 </td><td> 270 </td><td> 40 </td> <td> 58.0 </td><td> 651 </td></tr> +<tr><td style="text-align: left;" rowspan="1" colspan="15"><i>Note.—Following is an + explanation of the abbreviations used in the foregoing tables:</i><br> + F.S. at E.L. = Fiber stress at elastic limit.<br> + M. of E. = Modulus of elasticity.<br> + M. of R. = Modulus of rupture.<br> + Cr. str. at E.L. = Crushing strength at elastic limit.<br> + Cr. str. at max. ld. = Crushing strength at maximum load. </td></tr> +</tbody> +</table> +</center> + +<a name="pg142"></a> + +<center> +<table id="TABLE_20" summary="TABLE_XX" border="3" cellspacing="0" cellpadding="1" width="100%"> +<tbody> +<tr><th colspan="14"> TABLE XX </th></tr> +<tr><th colspan="14"> BENDING TESTS ON AIR-SEASONED MATERIAL </th></tr> +<tr><th rowspan="3"> Species </th> <th colspan="2"> Sizes </th> <th rowspan="2"> Number of tests </th> + <th rowspan="2"> Per cent of moisture </th> + <th rowspan="2"> Rings per inch </th> + <th colspan="2"> F.S. at E.L. </th> + <th colspan="2"> M. of R. </th> <th colspan="2"> M. of E. </th><th colspan="2"> Calculated shear </th></tr> +<tr> <th> Cross Section </th> + <th> Span </th> + <th> Average per sq. inch </th> + <th> Ratio to 2" by 2" </th> + <th> Average per sq. inch </th> + <th> Ratio to 2" by 2" </th> + <th> Average per sq. inch </th> + <th> Ratio to 2" by 2" </th> + <th> Average per sq. inch </th> + <th> Ratio to 2" by 2" </th></tr> +<tr> <th><i>Inches</i></th> + <th><i>Ins.</i></th> + <th><br></th> <th><br></th> <th><br></th> <th><i>Lbs.</i></th> + <th><br></th> <th><i>Lbs.</i></th> + <th><br></th> <th> 1,000 <i>lbs.</i></th> + <th><br></th> <th><i>Lbs.</i></th> + <th><br></th></tr> +<tr><td style="text-align: left;"> Longleaf pine </td> <td> 8 by 16 </td><td> 180 </td><td> 5 </td> <td> 22.2 </td><td> 16.0 </td><td> 3,390 </td><td> 0.50 </td><td> 4,274 </td> <td> 0.37 </td><td> 1,747 </td><td> 1.00 </td><td> 288 </td><td> 0.75 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 6 by 16 </td><td> 132 </td><td> 1 </td> <td> 23.4 </td><td> 17.1 </td><td> 3,470 </td><td> .51 </td> <td> 6,610 </td> <td> .57 </td> <td> 1,501 </td><td> .86 </td> <td> 388 </td><td> 1.01 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 6 by 10 </td><td> 177 </td><td> 2 </td> <td> 19.0 </td><td> 8.8 </td> <td> 4,560 </td><td> .68 </td> <td> 7,880 </td> <td> .68 </td> <td> 1,722 </td><td> .99 </td> <td> 214 </td><td> .56 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 11 </td><td> 180 </td><td> 1 </td> <td> 18.4 </td><td> 23.9 </td><td> 3,078 </td><td> .46 </td> <td> 8,000 </td> <td> .69 </td> <td> 1,660 </td><td> .95 </td> <td> 251 </td><td> .66 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 6 by 8 </td> <td> 177 </td><td> 6 </td> <td> 20.0 </td><td> 13.7 </td><td> 4,227 </td><td> .63 </td> <td> 8,196 </td> <td> .71 </td> <td> 1,634 </td><td> .94 </td> <td> 177 </td><td> .46 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 30 </td> <td> 17 </td> <td> 15.9 </td><td> 13.9 </td><td> 6,750 </td><td> 1.00 </td><td> 11,520 </td><td> 1.00 </td><td> 1,740 </td><td> 1.00 </td><td> 383 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Douglas fir </td> <td> 8 by 16 </td><td> 180 </td><td> 91 </td> <td> 20.8 </td><td> 13.1 </td><td> 4,563 </td><td> .68 </td> <td> 6,372 </td> <td> .61 </td> <td> 1,549 </td><td> .91 </td> <td> 269 </td><td> .64 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 5 by 8 </td> <td> 180 </td><td> 30 </td> <td> 14.9 </td><td> 12.2 </td><td> 5,065 </td><td> .76 </td> <td> 6,777 </td> <td> .65 </td> <td> 1,853 </td><td> 1.09 </td><td> 218 </td><td> .52 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 24 </td> <td> 211 </td><td> 19.0 </td><td> 16.4 </td><td> 6,686 </td><td> 1.00 </td><td> 10,378 </td><td> 1.00 </td><td> 1,695 </td><td> 1.00 </td><td> 419 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Shortleaf pine </td> <td> 8 by 16 </td><td> 180 </td><td> 3 </td> <td> 17.0 </td><td> 12.3 </td><td> 4,220 </td><td> .54 </td> <td> 6,030 </td> <td> .50 </td> <td> 1,517 </td><td> .85 </td> <td> 398 </td><td> .98 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 8 by 14 </td><td> 180 </td><td> 3 </td> <td> 16.0 </td><td> 12.3 </td><td> 4,253 </td><td> .55 </td> <td> 5,347 </td> <td> .44 </td> <td> 1,757 </td><td> .98 </td> <td> 307 </td><td> .76 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 8 by 12 </td><td> 180 </td><td> 7 </td> <td> 16.0 </td><td> 12.4 </td><td> 5,051 </td><td> .65 </td> <td> 7,331 </td> <td> .60 </td> <td> 1,803 </td><td> 1.01 </td><td> 361 </td><td> .89 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 5 by 8 </td> <td> 180 </td><td> 6 </td> <td> 12.2 </td><td> 22.5 </td><td> 7,123 </td><td> .92 </td> <td> 9,373 </td> <td> .77 </td> <td> 1,985 </td><td> 1.11 </td><td> 301 </td><td> .74 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 30 </td> <td> 67 </td> <td> 14.2 </td><td> 13.7 </td><td> 7,780 </td><td> 1.00 </td><td> 12,120 </td><td> 1.00 </td><td> 1,792 </td><td> 1.00 </td><td> 404 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Western larch </td> <td> 8 by 16 </td><td> 180 </td><td> 23 </td> <td> 18.3 </td><td> 21.9 </td><td> 3,343 </td><td> .57 </td> <td> 5,440 </td> <td> .53 </td> <td> 1,409 </td><td> .90 </td> <td> 349 </td><td> .96 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 8 by 12 </td><td> 180 </td><td> 29 </td> <td> 17.8 </td><td> 23.4 </td><td> 3,631 </td><td> .62 </td> <td> 6,186 </td> <td> .60 </td> <td> 1,549 </td><td> .99 </td> <td> 295 </td><td> .81 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 5 by 8 </td> <td> 180 </td><td> 10 </td> <td> 13.6 </td><td> 27.6 </td><td> 4,730 </td><td> .80 </td> <td> 7,258 </td> <td> .71 </td> <td> 1,620 </td><td> 1.04 </td><td> 221 </td><td> .61 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 30 </td> <td> 240 </td><td> 16.1 </td><td> 26.8 </td><td> 5,880 </td><td> 1.00 </td><td> 10,254 </td><td> 1.00 </td><td> 1,564 </td><td> 1.00 </td><td> 364 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Loblolly pine </td> <td> 8 by 16 </td><td> 180 </td><td> 14 </td> <td> 20.5 </td><td> 7.4 </td> <td> 4,195 </td><td> .81 </td> <td> 6,734 </td> <td> .72 </td> <td> 1,619 </td><td> 1.10 </td><td> 462 </td><td> 1.45 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 6 by 16 </td><td> 126 </td><td> 4 </td> <td> 20.2 </td><td> 5.0 </td> <td> 2,432 </td><td> .47 </td> <td> 4,295 </td> <td> .46 </td> <td> 1,324 </td><td> .90 </td> <td> 266 </td><td> .84 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 6 by 10 </td><td> 174 </td><td> 3 </td> <td> 21.3 </td><td> 4.7 </td> <td> 3,100 </td><td> .60 </td> <td> 6,167 </td> <td> .66 </td> <td> 1,449 </td><td> .99 </td> <td> 173 </td><td> .54 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 12 </td><td> 174 </td><td> 4 </td> <td> 19.8 </td><td> 4.7 </td> <td> 2,713 </td><td> .52 </td> <td> 5,745 </td> <td> .61 </td> <td> 1,249 </td><td> .85 </td> <td> 185 </td><td> .58 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 8 by 8 </td> <td> 180 </td><td> 9 </td> <td> 22.9 </td><td> 4.9 </td> <td> 2,903 </td><td> .56 </td> <td> 4,557 </td> <td> .48 </td> <td> 1,136 </td><td> .77 </td> <td> 93 </td> <td> .29 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 6 by 7 </td> <td> 144 </td><td> 2 </td> <td> 21.1 </td><td> 5.0 </td> <td> 2,990 </td><td> .58 </td> <td> 4,968 </td> <td> .53 </td> <td> 1,286 </td><td> .88 </td> <td> 116 </td><td> .36 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 8 </td> <td> 132 </td><td> 8 </td> <td> 19.5 </td><td> 9.1 </td> <td> 3,384 </td><td> .65 </td> <td> 6,194 </td> <td> .66 </td> <td> 1,200 </td><td> .82 </td> <td> 196 </td><td> .62 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 30 </td> <td> 123 </td><td> 17.6 </td><td> 6.6 </td> <td> 5,170 </td><td> 1.00 </td><td> 9,400 </td> <td> 1.00 </td><td> 1,467 </td><td> 1.00 </td><td> 318 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Tamarack </td> <td> 6 by 12 </td><td> 162 </td><td> 5 </td> <td> 23.0 </td><td> 15.1 </td><td> 3,434 </td><td> .45 </td> <td> 5,640 </td> <td> .43 </td> <td> 1,330 </td><td> .82 </td> <td> 318 </td><td> .75 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 10 </td><td> 162 </td><td> 4 </td> <td> 14.4 </td><td> 9.7 </td> <td> 4,100 </td><td> .54 </td> <td> 5,320 </td> <td> .41 </td> <td> 1,386 </td><td> .84 </td> <td> 252 </td><td> .59 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 30 </td> <td> 47 </td> <td> 11.3 </td><td> 16.2 </td><td> 7,630 </td><td> 1.00 </td><td> 13,080 </td><td> 1.00 </td><td> 1,620 </td><td> 1.00 </td><td> 425 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Western hemlock </td><td> 8 by 16 </td><td> 180 </td><td> 44 </td> <td> 17.7 </td><td> 17.8 </td><td> 4,398 </td><td> .69 </td> <td> 6,420 </td> <td> .62 </td> <td> 1,737 </td><td> 1.04 </td><td> 406 </td><td> 1.06 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 28 </td> <td> 311 </td><td> 17.9 </td><td> 19.4 </td><td> 6,333 </td><td> 1.00 </td><td> 10,369 </td><td> 1.00 </td><td> 1,666 </td><td> 1.00 </td><td> 382 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Redwood </td> <td> 8 by 16 </td><td> 180 </td><td> 6 </td> <td> 26.3 </td><td> 22.4 </td><td> 3,797 </td><td> .79 </td> <td> 4,428 </td> <td> .57 </td> <td> 1,107 </td><td> .96 </td> <td> 294 </td><td> 1.05 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 6 by 12 </td><td> 180 </td><td> 6 </td> <td> 16.1 </td><td> 17.7 </td><td> 3,175 </td><td> .66 </td> <td> 3,353 </td> <td> .43 </td> <td> 728 </td> <td> .64 </td> <td> 167 </td><td> .60 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 7 by 9 </td> <td> 180 </td><td> 6 </td> <td> 15.9 </td><td> 15.2 </td><td> 3,280 </td><td> .69 </td> <td> 4,002 </td> <td> .51 </td> <td> 1,104 </td><td> .96 </td> <td> 147 </td><td> .53 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 3 by 14 </td><td> 180 </td><td> 6 </td> <td> 13.1 </td><td> 24.4 </td><td><br></td> <td><br></td> <td> 5,033 </td> <td> .64 </td> <td><br></td> <td><br></td> <td> 291 </td><td> 1.04 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 12 </td><td> 180 </td><td> 5 </td> <td> 13.8 </td><td> 14.4 </td><td> 3,928 </td><td> .82 </td> <td> 5,336 </td> <td> .68 </td> <td> 1,249 </td><td> 1.09 </td><td> 260 </td><td> .93 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 10 </td><td> 180 </td><td> 5 </td> <td> 13.8 </td><td> 24.8 </td><td> 3,757 </td><td> .79 </td> <td> 4,606 </td> <td> .59 </td> <td> 1,198 </td><td> 1.05 </td><td> 186 </td><td> .67 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 8 </td> <td> 180 </td><td> 6 </td> <td> 13.7 </td><td> 20.7 </td><td> 4,314 </td><td> .90 </td> <td> 5,050 </td> <td> .65 </td> <td> 1,313 </td><td> 1.15 </td><td> 166 </td><td> .60 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 28 </td> <td> 122 </td><td> 15.2 </td><td> 18.8 </td><td> 4,777 </td><td> 1.00 </td><td> 7,798 </td> <td> 1.00 </td><td> 1,146 </td><td> 1.00 </td><td> 279 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;"> Norway pine </td> <td> 6 by 12 </td><td> 162 </td><td> 5 </td> <td> 16.7 </td><td> 8.1 </td> <td> 2,968 </td><td> .56 </td> <td> 5,204 </td> <td> .61 </td> <td> 1,123 </td><td> .97 </td> <td> 286 </td><td> 1.02 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 10 </td><td> 162 </td><td> 5 </td> <td> 13.7 </td><td> 12.0 </td><td> 5,170 </td><td> .98 </td> <td> 6,904 </td> <td> .82 </td> <td> 1,712 </td><td> 1.48 </td><td> 317 </td><td> 1.13 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td> <td> 30 </td> <td> 60 </td> <td> 14.9 </td><td> 11.2 </td><td> 5,280 </td><td> 1.00 </td><td> 8,470 </td> <td> 1.00 </td><td> 1,158 </td><td> 1.00 </td><td> 281 </td><td> 1.00 </td></tr> +<tr><td style="text-align: left;" colspan="14"> <i>Note.—Following is an + explanation of the abbreviations used in the foregoing tables:</i><br> + F.S. at E.L. = Fiber stress at elastic limit.<br> + M. of E. = Modulus of elasticity.<br> + M. of R. = Modulus of rupture.<br> + Cr. str. at E.L. = Crushing strength at elastic limit.<br> + Cr. str. at max. ld. = Crushing strength at maximum load. </td></tr> +</tbody> +</table> +</center> + +<a name="pg143"></a> + +<center> +<table id="TABLE_21" summary="TABLE_XXI" border="3" cellspacing="0" cellpadding="1" width="100%"> +<tbody> +<tr><th colspan="15"> TABLE XXI </th></tr> +<tr><th colspan="15"> COMPRESSION AND SHEAR TESTS ON AIR-SEASONED MATERIAL </th></tr> +<tr><th rowspan="3"> Species </th> <th colspan="6"> Compression parallel to grain </th> <th colspan="5"> Compression perpendicular to grain </th> <th colspan="3"> Shear </th></tr> +<tr> <th> Size of specimen </th> + <th> No. of tests </th> + <th> Per cent of moisture </th> + <th> Cr. str. at E. L. per square inch </th> + <th> M. of E. per square inch </th> + <th> Cr. str. at max. ld., per square inch </th> + <th> Stress area </th> + <th> Height </th> + <th> No. of tests </th> + <th> Per cent of moisture </th> + <th> Cr. str. at max. ld., per square inch </th> + <th> No. of tests </th> + <th> Per cent of moisture </th> + <th> Shear strength </th></tr> +<tr> <th><i>Inches</i></th> + <th><br></th> <th><br></th> <th><i>Lbs.</i></th> + <th> 1,000 <i>lbs.</i></th> + <th><i>Lbs.</i></th> + <th><i>Inches</i></th> + <th><i>Inches</i></th> + <th><br></th> <th><br></th> <th><i>Lbs.</i></th> + <th><br></th> <th><br></th> <th><i>Lbs.</i></th></tr> +<tr><td style="text-align: left;"> Longleaf pine </td> <td> 4 by 5 </td><td> 46 </td> <td> 26.3 </td><td> 3,480 </td><td><br></td> <td> 4,800 </td><td> 4 by 5 </td><td> 4 </td> <td> 22 </td> <td> 25.1 </td><td> 572 </td><td> 52 </td> <td> 20.2 </td><td> 984 </td></tr> +<tr><td style="text-align: left;"> Douglas fir </td> <td> 6 by 6 </td><td> 259 </td><td> 20.3 </td><td> 3,271 </td><td> 1,038 </td><td> 4,258 </td><td> 4 by 8 </td><td> 16 </td><td> 44 </td> <td> 20.8 </td><td> 732 </td><td> 465 </td><td> 22.1 </td><td> 822 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 247 </td><td> 18.7 </td><td> 3,842 </td><td> 1,084 </td><td> 5,002 </td><td> 4 by 8 </td><td> 10 </td><td> 32 </td> <td> 18.1 </td><td> 584 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 4 by 4 </td><td> 8 </td> <td> 51 </td> <td> 20.2 </td><td> 638 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> <br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 4 by 4 </td><td> 6 </td> <td> 49 </td> <td> 24.0 </td><td> 613 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 4 by 4 </td><td> 4 </td> <td> 29 </td> <td> 24.8 </td><td> 603 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Shortleaf pine </td> <td> 6 by 6 </td><td> 29 </td> <td> 15.7 </td><td> 4,070 </td><td> 1,951 </td><td> 6,030 </td><td> 8 by 5 </td><td> 16 </td><td> 4 </td> <td> 17.8 </td><td> 725 </td><td> 85 </td> <td><br></td> <td> 1,135 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 57 </td> <td> 14.2 </td><td><br></td> <td><br></td> <td> 6,380 </td><td> 8 by 5 </td><td> 14 </td><td> 3 </td> <td> 16.3 </td><td> 757 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 8 by 5 </td><td> 12 </td><td> 5 </td> <td> 15.1 </td><td> 730 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 5 by 5 </td><td> 8 </td> <td> 6 </td> <td> 13.0 </td><td> 918 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 2 by 2 </td><td> 2 </td> <td> 57 </td> <td> 13.9 </td><td> 926 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Western larch </td> <td> 6 by 6 </td><td> 112 </td><td> 16.0 </td><td><br></td> <td><br></td> <td> 5,445 </td><td> 8 by 6 </td><td> 16 </td><td> 17 </td> <td> 18.8 </td><td> 491 </td><td> 193 </td><td> 15.0 </td><td> 905 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 4 </td><td> 81 </td> <td> 14.7 </td><td><br></td> <td><br></td> <td> 6,161 </td><td> 8 by 6 </td><td> 12 </td><td> 18 </td> <td> 17.6 </td><td> 526 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 270 </td><td> 14.8 </td><td><br></td> <td><br></td> <td> 5,934 </td><td> 5 by 4 </td><td> 8 </td> <td> 22 </td> <td> 13.3 </td><td> 735 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Loblolly pine </td> <td> 6 by 6 </td><td> 23 </td> <td><br></td> <td> 3,357 </td><td> 1,693 </td><td> 5,005 </td><td> 8 by 5 </td><td> 16 </td><td> 12 </td> <td> 19.8 </td><td> 602 </td><td> 156 </td><td> 11.3 </td><td> 1,115 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 5 by 5 </td><td> 10 </td> <td> 22.4 </td><td> 2,217 </td><td> 545 </td> <td> 2,950 </td><td> 8 by 5 </td><td> 8 </td> <td> 7 </td> <td> 22.9 </td><td> 679 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 8 </td><td> 8 </td> <td> 19.4 </td><td> 3,010 </td><td> 633 </td> <td> 3,920 </td><td> 4 by 5 </td><td> 8 </td> <td> 8 </td> <td> 19.5 </td><td> 715 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 69 </td> <td><br></td> <td><br></td> <td><br></td> <td> 5,547 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Tamarack </td> <td> 6 by 7 </td><td> 3 </td> <td> 15.7 </td><td> 2,257 </td><td> 1,042 </td><td> 3,323 </td><td> 2 by 2 </td><td> 2 </td> <td> 57 </td> <td> 16.2 </td><td> 697 </td><td> 60 </td> <td> 14.0 </td><td> 879 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 7 </td><td> 3 </td> <td> 13.6 </td><td> 3,780 </td><td> 1,301 </td><td> 4,823 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 4 </td><td> 57 </td> <td> 14.9 </td><td> 3,386 </td><td> 1,353 </td><td> 4,346 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 66 </td> <td> 14.6 </td><td><br></td> <td><br></td> <td> 4,790 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Western hemlock </td><td> 6 by 6 </td><td> 102 </td><td> 18.6 </td><td> 4,840 </td><td> 2,140 </td><td> 5,814 </td><td> 7 by 6 </td><td> 15 </td><td> 25 </td> <td> 18.2 </td><td> 514 </td><td> 131 </td><td> 17.7 </td><td> 924 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 463 </td><td> 17.0 </td><td> 4,560 </td><td> 1,923 </td><td> 5,403 </td><td> 6 by 6 </td><td> 6 </td> <td> 26 </td> <td> 16.8 </td><td> 431 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 4 by 4 </td><td> 4 </td> <td> 6 </td> <td> 15.9 </td><td> 488 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Redwood </td> <td> 6 by 6 </td><td> 18 </td> <td> 16.9 </td><td><br></td> <td><br></td> <td> 4,276 </td><td> 8 by 6 </td><td> 16 </td><td> 5 </td> <td> 25.4 </td><td> 548 </td><td> 95 </td> <td> 12.4 </td><td> 671 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 115 </td><td> 14.6 </td><td><br></td> <td><br></td> <td> 5,119 </td><td> 6 by 6 </td><td> 12 </td><td> 6 </td> <td> 14.7 </td><td> 610 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 7 by 6 </td><td> 9 </td> <td> 5 </td> <td> 14.8 </td><td> 500 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 3 by 6 </td><td> 14 </td><td> 2 </td> <td> 12.6 </td><td> 470 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 2 by 6 </td><td> 12 </td><td> 2 </td> <td> 16.2 </td><td> 498 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 2 by 6 </td><td> 10 </td><td> 4 </td> <td> 14.3 </td><td> 511 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 2 by 6 </td><td> 8 </td> <td> 2 </td> <td> 13.2 </td><td> 429 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 2 by 2 </td><td> 2 </td> <td> 145 </td><td> 13.8 </td><td> 564 </td><td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"> Norway pine </td> <td> 6 by 7 </td><td> 4 </td> <td> 15.2 </td><td> 2,670 </td><td> 1,182 </td><td> 4,212 </td><td> 2 by 2 </td><td> 2 </td> <td> 36 </td> <td> 10.0 </td><td> 924 </td><td> 44 </td> <td> 11.9 </td><td> 1,145 </td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 7 </td><td> 2 </td> <td> 22.2 </td><td> 3,275 </td><td> 1,724 </td><td> 4,575 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td> 4 by 4 </td><td> 55 </td> <td> 16.6 </td><td> 3,048 </td><td> 1,367 </td><td> 4,217 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;"><br></td> <td> 2 by 2 </td><td> 44 </td> <td> 11.2 </td><td><br></td> <td><br></td> <td> 7,550 </td><td><br></td> <td><br></td><td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td><br></td></tr> +<tr><td style="text-align: left;" rowspan="1" colspan="15"><i>Note.—Following is an explanation of the abbreviations used in the foregoing tables:</i><br> F.S. at E.L. = Fiber stress at elastic limit.<br> M. of E. = Modulus of elasticity.<br> M. of R. = Modulus of rupture.<br> Cr. str. at E.L. = Crushing strength at elastic limit.<br> Cr. str. at max. ld. = Crushing strength at maximum load. </td></tr> +</tbody> +</table> +</center> + +<a name="pg144"></a> + +<center> +<table id="TABLE_22" summary="TABLE_XXII" border="3" cellspacing="0" cellpadding="1" width="100%"> +<tbody> +<tr><th colspan="15"> TABLE XXII </th></tr> +<tr><th colspan="15"> [b]WORKING UNIT-STRESSES FOR STRUCTURAL TIMBER[c] </th></tr> +<tr><th colspan="15"> EXPRESSED IN POUNDS PER SQUARE INCH </th></tr> +<tr><td colspan="15"> (From Manual of the American Railway Engineering Assn., 1911, p. 153) </td></tr> +<tr><td style="text-align: left;" colspan="15"> NOTE.—The working unit-stresses given in the table are intended for railroad bridges and trestles. For highway bridges and trestles the unit-stresses may be increased twenty-five (25) per cent. For buildings and similar structures, in which the timber is protected from the weather and practically free from impact, the unit-stresses may be increased fifty (50) per cent. To compute the deflection of a beam under long-continued loading instead of that when the load is first applied, only fifty (50) per cent of the corresponding modulus of elasticity given in the table is to be employed. </td></tr> +<tr><th rowspan="3" > KIND OF TIMBER </th> <th colspan="3"> BENDING </th> <th colspan="4"> SHEARING </th> <th colspan="6"> COMPRESSION </th> <th rowspan="3"> Ratio of length of stringer to depth </th></tr> +<tr> <th colspan="2"> Extreme fibre stress </th> + <th> Modulus of elasticity </th> + <th colspan="2"> Parallel to the grain </th> + <th colspan="2"> Longitudinal shear in beams </th> + <th colspan="2"> Perpendicular to the grain </th> + <th colspan="2"> Parallel to the grain </th> + <th rowspan="2"> For columns under 15 diameters working stress </th> + <th rowspan="2"> Formulæ for working stress in long columns over 15 diameters </th></tr> +<tr> <th> Average ultimate </th> + <th> Working stress </th> + <th> Average </th> <th> Average ultimate </th> + <th> Working stress </th> + <th> Average ultimate </th> + <th> Working stress </th> + <th> Elastic limit </th> + <th> Working stress </th> + <th> Average ultimate </th> + <th> Working stress </th></tr> +<tr><td style="text-align: left;"> Douglas fir </td> <td> 6100 </td><td> 1200 </td><td> 1,510,000 </td><td> 690 </td> <td> 170 </td><td> 270 </td> <td> 110 </td><td> 630 </td><td> 310 </td><td> 3600 </td> <td> 1200 </td><td> 900 </td><td> 1200 (1 - <i>l </i>/ 60 <i>d</i>) </td><td> 10 </td></tr> +<tr><td style="text-align: left;"> Longleaf pine </td> <td> 6500 </td><td> 1300 </td><td> 1,610,000 </td><td> 720 </td> <td> 180 </td><td> 300 </td> <td> 120 </td><td> 520 </td><td> 260 </td><td> 3800 </td> <td> 1300 </td><td> 980 </td><td> 1300 (1 - <i>l </i>/ 60 <i>d</i>) </td><td> 10 </td></tr> +<tr><td style="text-align: left;"> Shortleaf pine </td> <td> 5600 </td><td> 1100 </td><td> 1,480,000 </td><td> 710 </td> <td> 170 </td><td> 330 </td> <td> 130 </td><td> 340 </td><td> 170 </td><td> 3400 </td> <td> 1100 </td><td> 830 </td><td> 1100 (1 - <i>l </i>/ 60 <i>d</i>) </td><td> 10 </td></tr> +<tr><td style="text-align: left;"> White pine </td> <td> 4400 </td><td> 900 </td> <td> 1,130,000 </td><td> 400 </td> <td> 100 </td><td> 180 </td> <td> 70 </td> <td> 290 </td><td> 150 </td><td> 3000 </td> <td> 1000 </td><td> 750 </td><td> 1000 (1 - <i>l </i>/ 60 <i>d</i>) </td><td> 10 </td></tr> +<tr><td style="text-align: left;"> Spruce </td> <td> 4800 </td><td> 1000 </td><td> 1,310,000 </td><td> 600 </td> <td> 150 </td><td> 170 </td> <td> 70 </td> <td> 370 </td><td> 180 </td><td> 3200 </td> <td> 1100 </td><td> 830 </td><td> 1100 (1 - <i>l </i>/ 60 <i>d</i>) </td><td><br></td></tr> +<tr><td style="text-align: left;"> Norway pine </td> <td> 4200 </td><td> 800 </td> <td> 1,190,000 </td><td> 590[d] </td><td> 130 </td><td> 250 </td> <td> 100 </td><td><br></td> <td> 150 </td><td> 2600[d] </td><td> 800 </td> <td> 600 </td><td> 800 (1 - <i>l </i>/ 60 <i>d</i>) </td><td><br></td></tr> +<tr><td style="text-align: left;"> Tamarack </td> <td> 4600 </td><td> 900 </td> <td> 1,220,000 </td><td> 670 </td> <td> 170 </td><td> 260 </td> <td> 100 </td><td><br></td> <td> 220 </td><td> 3200[d] </td><td> 1000 </td><td> 750 </td><td> 1000 (1 - <i>l </i>/ 60 <i>d</i>) </td><td><br></td></tr> +<tr><td style="text-align: left;"> Western hemlock </td><td> 5800 </td><td> 1100 </td><td> 1,480,000 </td><td> 630 </td> <td> 160 </td><td> 270[d] </td><td> 100 </td><td> 440 </td><td> 220 </td><td> 3500 </td> <td> 1200 </td><td> 900 </td><td> 1200 (1 - <i>l </i>/ 60 <i>d</i>) </td><td><br></td></tr> +<tr><td style="text-align: left;"> Redwood </td> <td> 5000 </td><td> 900 </td> <td> 800,000 </td> <td> 300 </td> <td> 80 </td> <td><br></td> <td><br></td> <td> 400 </td><td> 150 </td><td> 3300 </td> <td> 900 </td> <td> 680 </td><td> 900 (1 - <i>l </i>/ 60 <i>d</i> )</td><td><br></td></tr> +<tr><td style="text-align: left;"> Bald cypress </td> <td> 4800 </td><td> 900 </td> <td> 1,150,000 </td><td> 500 </td> <td> 120 </td><td><br></td> <td><br></td> <td> 340 </td><td> 170 </td><td> 3900 </td> <td> 1100 </td><td> 830 </td><td> 1100 (1 - <i>l </i>/ 60 <i>d</i>) </td><td><br></td></tr> +<tr><td style="text-align: left;"> Red cedar </td> <td> 4200 </td><td> 800 </td> <td> 800,000 </td> <td><br></td> <td><br></td> <td><br></td> <td><br></td> <td> 470 </td><td> 230 </td><td> 2800 </td> <td> 900 </td> <td> 680 </td><td> 900 (1 - <i>l </i>/ 60 <i>d</i>) </td><td><br></td></tr> +<tr><td style="text-align: left;"> White oak </td> <td> 5700 </td><td> 1100 </td><td> 1,150,000 </td><td> 840 </td> <td> 210 </td><td> 270 </td> <td> 110 </td><td> 920 </td><td> 450 </td><td> 3500 </td> <td> 1300 </td><td> 980 </td><td> 1300 (1 - <i>l </i>/ 60 <i>d</i>) </td><td> 12 </td></tr> +<tr><td style="text-align: left;" rowspan="1" colspan="13"> These unit-stresses are for a green condition of timber and are to be used without increasing the live load stresses for impact. </td><td rowspan="1" colspan="2"><i>l</i> = Length in inches.<br><i>d</i> = Least side in inches.</td></tr> +<tr><td style="text-align: left;" rowspan="1" colspan="15">[Footnote b: Adopted, Vol. 1909, pp. 537, 564, 609-611.]<br></td></tr> +<tr><td style="text-align: left;" rowspan="1" colspan="15">[Footnote c: Green timber in exposed work.]<br></td></tr> +<tr><td style="text-align: left;" rowspan="1" colspan="15">[Footnote d: Partially air-dry]<br></td></tr> +</tbody> +</table> +</center> + +<a name="pg145"></a> +<a name="BIBLIOGRAPHY"></a><h2>BIBLIOGRAPHY</h2> + +<hr> + +<h4><a href="#BIB_I">Part I:</a> Some general works on mechanics, materials of construction, and testing of materials.</h4> +<h4><a href="#BIB_II">Part II:</a> Publications and articles on the mechanical properties of wood, and timber testing.</h4> +<h4><a href="#BIB_III">Part III:</a> Publications of the U.S. Government on the mechanical properties of wood, and timber testing.</h4> + +<hr> + +<a name="pg146"></a> +<a name="pg147"></a> +<a name="BIB_I"></a> +<h3>PART I.<br>SOME GENERAL WORKS ON MECHANICS, MATERIALS OF CONSTRUCTION, AND TESTING OF MATERIALS</h3> + +<p>ALLAN, WILLIAM: Strength of beams under transverse loads. New +York, 1893.</p> + +<p>ANDERSON, SIR JOHN: The strength of materials and structures. +London, 1902.</p> + +<p>BARLOW, PETER: Strength of materials, 1st ed. 1817; rev. 1867.</p> + +<p>BURR, WILLIAM H.: The elasticity and resistance of the materials +of engineering. New York, 1911.</p> + +<p>CHURCH, IRVING P.: Mechanics of engineering. New York, 1911.</p> + +<p>HATFIELD, R.G.: Theory of transverse strain. 1877.</p> + +<p>HATT, W.K., and SCOFIELD, H.H.: Laboratory manual of testing +materials. New York, 1913.</p> + +<p>JAMESON, J.M.: Exercises in mechanics. (Wiley technical series.) +New York, 1913.</p> + +<p>JAMIESON, ANDREW: Strength of materials. (Applied mechanics and +mechanical engineering, Vol. II.) London, 1911.</p> + +<p>JOHNSON, J.B.: The materials of construction. New York, 1910.</p> + +<p>KENT, WILLIAM: The strength of materials. New York, 1890.</p> + +<p>KOTTCAMP, J.P.: Exercises for the applied mechanics laboratory. +(Wiley technical series.) New York, 1913.</p> + +<p>LANZA, GAETANO: Applied mechanics. New York, 1901.</p> + +<p>MERRIMAN, MANSFIELD: Mechanics of materials. New York, 1912.</p> + +<p>MURDOCK, H.E.: Strength of materials. New York, 1911.</p> + +<p>RANKINE, WILLIAM J.M.: A manual of applied mechanics. London, +1901.</p> + +<p>THIL, A.: Conclusion de l'étude présentée à la Commission des +méthodes d'essai des matériaux de construction. Paris, 1900.</p> + +<p>THURSTON, ROBERT H.: A treatise on non-metallic materials of +engineering: stone, timber, fuel, lubricants, etc. (Materials of +engineering, Part I.) New York, 1899.</p> + +<p>UNWIN, WILLIAM C.: The testing of materials of construction. +London, 1899.</p> + +<p>WATERBURY, L.A.: Laboratory manual for testing materials of +construction. New York, 1912.</p> + +<p>WOOD, DEVOLSON: A treatise on the resistance of materials. New +York, 1897.</p> + +<a name="pg148"></a> +<a name="BIB_II"></a> +<h3>PART II.<br>PUBLICATIONS AND ARTICLES ON THE MECHANICAL PROPERTIES OF WOOD, AND TIMBER TESTING</h3> + +<p>ABBOT, ARTHUR V.: Testing machines, their history, construction +and use. Van Nostrand's Eng. Mag., Vol. XXX, 1884, pp. 204-214; +325-344; 382-397; 477-490.</p> + +<p>ADAMS, E.E.: Tests to determine the strength of bolted timber +joints. Cal. Jour, of Technology, Sept., 1904.</p> + +<p>ALVAREZ, ARTHUR C.: The strength of long seasoned Douglas fir +and redwood. Univ. of Cal. Pub. in Eng., Vol. I, No. 2, +Berkeley, 1913, pp. 11-20.</p> + +<p>BARLOW, PETER: An essay on the strength and stress of timber. +London, 1817; 3d ed., 1826.</p> + +<p>——: Experiments on the strength of different kinds of wood +made in the carriage department, Royal Arsenal, Woolwich. Jour. +Franklin Inst., Vol. X, 1832, pp. 49-52. Reprinted from +Philosophical Mag. and Annals of Philos., No. 63, Mch., 1832.</p> + +<p>BATES, ONWARD: Pine stringers and floorbeams for bridges. Trans. +Am. Soc. C.E., Vol. XXIII.</p> + +<p>BAUSCHINGER, JOHANN: Untersuchungen über die Elasticität und +Festigkeit von Fichten- und Kiefernbauhölzern. Mitt. a. d. +mech.-tech. Laboratorium d. k. techn. Hochschule in München, 9. +Hft., München, 1883.</p> + +<p>——: Verhandlungen der Münchener Conferenz und der von ihr +gewählten ständigen Commission zur Vereinbarung einheitlicher +Prüfungsmethoden für Bau- und Constructions-material. <i>Ibid.</i>, +14. Hft., 1886.</p> + +<p>——: Untersuchungen über die Elasticität und Festigkeit +verschiedener Nadelhölzer. <i>Ibid.</i>, 16. Hft., 1887.</p> + +<p>BEARE, T. HUDSON: Timber: its strength and how to test it. +Engineering, London, Dec. 9, 1904.</p> + +<p>BEAUVERIE, J.: Le bois. I. Paris, 1905, pp. 105-185.</p> + +<p>——: Les bois industriels. Paris, 1910, pp. 55-77. Bending +tests with wood, executed at the Danish State Testing +Laboratory, Copenhagen. Proc. Int. Assn. Test. Mat., 1912, +XXIII<sub><small>2</small></sub>, pp. 17. See also Eng. Record, Vol. LXVI, 1912, p. +269.</p> + +<p>BERG, WALTER G.: Berg's complete timber test record. Chicago, +1899. Reprint from Am. By. Bridges and Buildings. BOULGER, G.S.: +Wood. London, 1908, pp. 112-121.</p> + +<p>BOUNICEAU,—: Note et expériences sur la torsion des bois. +[N.p., n.d.]</p> + +<p>BOVEY, HENRY T.: Results of experiments at McGill University, +<a name="pg149"></a> +Montreal, on the strength of Canadian Douglas fir, red pine, +white pine, and spruce. Trans. Can. Soc. C.E., Vol. IX, Part I, +1895, pp. 69-236.</p> + +<p>BREUIL, M. PIERRE: Contribution to the discussion on the testing +of wood. Proc. Int. Assn. Test. Mat., 1906, Disc, 1<i>e</i>, pp. 2.</p> + +<p>BROWN, T.S.: An Account of some experiments made by order of +Col. Totten, at Fort Adams, Newport, R.I., to ascertain the +relative stiffness and strength of the following kinds of +timber, viz.: white pine (<i>Pinus strobus</i>), spruce (<i>Abies +nigra</i>), and southern pine (<i>Pinus australis</i>), also called +long-leaved pine. Jour. Franklin Inst., Vol. VII (n.s.), 1831, +pp. 230-238.</p> + +<p>BUCHANAN, C.P.: Some tests of old timber. Eng. News, Vol. LXIV, +No. 23, 1910, p. 67.</p> + +<p>BUSGEN, M.: Zur Bestimmung der Holzhärten. Zeitschrift f. Forst- +und Jagdwesen. Berlin, 1904, pp. 543-562.</p> + +<p>CHEVANDIER, E., et WERTHEIM, G.: Mémoire sur les propriétés +mécaniques du bois. Paris, 1846.</p> + +<p>CIESLAR, A.: Studien über die Qualität rasch erwachsenen +Fichtenholzes. Centralblatt f. d. ges. Forstwesen, Wien, 1902, +pp. 337-403.</p> + +<p>CLINE, McGARVEY: Forest Service investigations of American woods +with special reference to investigations of mechanical +properties. Proc. Int. Assn. Test. Mat., 1912, XXIII<sub><small>5</small></sub>, pp. +17.</p> + +<p>——: Forest Service tests to determine the influence of +different methods and rates of loading on the strength and +stiffness of timber. Proc. Am. Soc. Test. Mat., Vol. VIII, 1908, +pp. 535-540.</p> + +<p>——: The Forest Products Laboratory: its purpose and work. +Proc. Am. Soc. Test. Mat., Vol. X, 1910, pp. 477-489.</p> + +<p>——: Specifications and grading rules for Douglas fir timber: +an analysis of Forest Service tests on structural timbers. Proc. +Am. Soc. Test. Mat., Vol. XI, 1911, pp. 744-766.</p> + +<p>Comparative strength and resistance of various tie timbers. +Elec. Traction Weekly, Chicago, June 15, 1912.</p> + +<p>DAY, FRANK M.: Microscopic examination of timber with regard to +its strength. 1883, pp. 6.</p> + +<p>DEWELL, H.D.: Tests of some joints used in heavy timber framing. +Eng. News, Mch. 19, 1914, pp. 594-598; <i>et seq.</i></p> + +<p>DÖRR, KARL: Die Festigkeit von Fichten- und Kiefernholz. +Deutsche Bauzeitung, Berlin, Aug. 17, 1910. See also Zeitschrift +d. ver. deutsch. Ing., Bd. 54, Nr. 36, 1910, p. 1503.</p> + +<p>DUPIN, CHARLES: Expériences sur la flexibilité, la force, et +l'élasticité des bois. Jour, de l'École Polytechnique, Vol. X, +1815.</p> + +<p>DUPONT, ADOLPHE, et BOUQUET DE LA GRYE: Les bois indigènes et +étrangers. Paris, 1875, pp. 273-352.</p> + +<a name="pg150"></a> + +<p>ESTRADA, ESTEBAN DUQUE: On the strength and other properties of +Cuban woods. Van Nostrand's Eng. Mag., Vol. XXIX, 1883, pp. +417-426; 443-449.</p> + +<p>EVERETT, W.H.: Memorandum on mechanical tests of some Indian +timbers. Govt. Bul. No. 6 (o.s.), Calcutta.</p> + +<p>EXNER, WILHELM FRANZ: Die mechanische Technologie des Holzes. +Wien, 1871. (A translation and revision of Chevandier and +Wertheim's Mémoire sur les propriétés mécaniques du bois.)</p> + +<p>——: Die technischen Eigenschaften der Hölzer. Lorey's Handbuch +der Forstwissenschaft, II. Bd., 6. Kap., Tübingen, 1903.</p> + +<p>FERNOW, B.E.: Scientific timber testing. Digest of Physical +Tests, Vol. I, No. 2, 1896, pp. 87-95.</p> + +<p>FOWKE, FRANCIS: Experiments on British colonial and other woods. +1867.</p> + +<p>GARDNER, ROLAND: I. Mechanical tests, properties, and uses of +thirty Philippine woods. II. Philippine sawmills, lumber market +and prices. Bul. 4, Bu. For., P.I., 1906. (2d ed., 1907, +contains tests of 34 woods.)</p> + +<p>GAYER, KARL: Forest utilization. (Vol. V, Schlich's Manual of +Forestry. Translation of Die Forstbenutzung, Berlin, 1894.) +London, 1908.</p> + +<p>GOLLNER, H.: Ueber die Festigkeit des Schwarzföhrenholzes. Mitt. +a. d. forstl. Versuchswesen Oesterreichs. II. Bd., 3. Hft., +Wien, 1881.</p> + +<p>GOTTGETREU, RUDOLPH: Physische und chemische Beschaffenheit der +Baumaterialien. 3d ed., Berlin, 1880.</p> + +<p>GREEN, A.O.: Tasmanian timbers: their qualities and uses. +Hobart, Tasmania, 1903, pp. 63.</p> + +<p>GREGORY, W.B.: Tests of creosoted timber. Trans. Am. Soc. C.E., +Vol. LXXVI, 1913, pp. 1192-1203. See also <i>ibid.</i>, Vol. LXX, p. +37.</p> + +<p>GRISARD, JULES, et VANDENBERGHE, MAXIMILIEN: Les bois +industriels, indigènes et exotiques; synonymie et description +des espèces, propriétés physiques des bois, qualités, défauts, +usages et emplois. Paris, 189-. From Bul. de la Société +nationale d'acclimatation de France, Vols. XXXVIII-XL.</p> + +<p>Hardwoods of Western Australia. Engineering, Vol. LXXXIII, Jan. +11, 1907, pp. 35-37.</p> + +<p>HATT, WILLIAM KENDRICK: A Preliminary program for the timber +test work to be undertaken by the Bureau of Forestry, United +States Department of Agriculture. Proc. Am. Soc. Test. Mat., +Vol. III, 1903, pp. 308-343. Appendix I: Method of determining +the effect of the rate of application of load on the strength of +timber, pp. 325-327; App. II: A discussion on the <a name="pg151"></a> effect of +moisture on strength and stiffness of timber, together with a +plan of procedure for future tests, pp. 328-334.</p> + +<p>HATT, WILLIAM KENDRICK: Relation of timber tests to forest +products. Proc. Int. Assn. Test. Mat., 1906, C 2 <i>e</i>, pp. 6.</p> + +<p>——: Structural timber. Proc. Western Ry. Club, St. Louis, Mch. +17, 1908.</p> + +<p>——: Abstract of report on the present status of timber tests +in the Forest Service, United States Department of Agriculture. +Proc. Int. Assn. Test. Mat., 1909, XVL, pp. 10.</p> + +<p>—— and TURNER, W.P.: The Purdue University impact machine. +Proc. Am. Soc. Test. Mat., Vol. VI, 1906, pp. 462-475.</p> + +<p>HAUPT, HERMAN: formulæ for the strain upon timber. Center of +gravity of an ungula and semi-cylinder. Jour. Franklin Inst., +Vol. XIX, 3d series, 1850, pp. 408-413.</p> + +<p>HEARDING, W.H.: Report upon experiments ... upon the compressive +power of pine and hemlock timber. Washington, 1872, pp. 12.</p> + +<p>HOWE, MALVERD A.: Wood in compression; bearing values for +inclined cuts. Eng. News, Vol. LXVIII, 1912, pp. 190-191.</p> + +<p>HOYER, EGBERT: Lehrbuch der vergleichenden mechanischen +Technologie. 1878.</p> + +<p>IHLSENG, MANGUS C.: On the modulus of elasticity of some +American woods as determined by vibration. Van Nostrand's Eng. +Mag., Vol. XIX, 1878, pp. 8-9.</p> + +<p>——: On a mode of measuring the velocity of sounds in woods. +Am. Jour. Sci. and Arts, Vol. XVII, 1879.</p> + +<p>JACCARD, P.: Étude anatomique des bois comprimés. Mitt. d. Schw. +Centralanstalt f. d. forst. Versuchswesen. X. Bd., 1. Hft., +Zurich, 1910, pp. 53-101.</p> + +<p>JANKA, GABRIEL: Untersuchungen über die Elasticität und +Festigkeit der österreichischen Bauhölzer. I. Fichte Südtirols; +II. Fichte von Nordtirol vom Wienerwalde und Erzgebirge; III. +Fichte aus den Karpaten, aus dem Böhmerwalde, Ternovanerwalde +und den Zentralalpen. Technische Qualität des Fichtenholzes im +allgemeinen; IV. Lärche aus dem Wienerwalde, aus Schlesien, +Nord- und Südtirol. Mitt. a. d. forst. Untersuchungswesen +Oesterreichs, Wien, 1900-13.</p> + +<p>——: Untersuchungen über Holzqualität. Centralblatt f. d. ges. +Forstwesen. Wien, 1904, pp. 95-115.</p> + +<p>——: Ueber neuere holztechnologische Untersuchungen. Oesterr. +Vierteljahresschrift für Forstwesen, Wien, 1906, pp. 248-269.</p> + +<p>——: Die Härte des Holzes. Centralblatt f. d. ges. Forstwesen, +Wien, 1906, pp. 193-202; 241-260.</p> + +<a name="pg152"></a> + +<p>JANKA, GABRIEL: Die Einwirkung von Süss- und Salzwässern auf die +gewerblichen Eigenschaften der Hauptholzarten. I. Teil. +Untersuchungen u. Ergebnisse in mechanisch-technischer Hinsicht. +Mitt. a. d. forst. Versuchswesen Oesterreichs, 33. Hft., Wien, +1907.</p> + +<p>——: Results of trials with timber carried out at the Austrian +forestry testing-station at Mariabrunn. Proc. Int. Assn. Test. +Mat., 1906, Disc. 2 <i>e</i>, pp. 7.</p> + +<p>——: Ueber die an der k. k. forstlichen Versuchsanstalt +Mariabrunnen gewonnenen Resultate der Holzfestigkeitsprüfungen. +Zeitschrift d. Oesterr. Ing. u. Arch. Ver., Wien, Aug. 9, 1907.</p> + +<p>——: Ueber Holzhärteprufüng. Centralblatt f. d. ges. +Forstwesen, Wien, 1908, pp. 443-456.</p> + +<p>——: Testing the hardness of wood by means of the ball test. +Proc. Int. Assn. Test. Mat., 1912, XXIII<sub><small>3</small></sub>.</p> + +<p>JENNY, K.: Untersuchungen über die Festigkeit der Hölzer aus den +Ländern der ungarischen Krone. Budapest, 1873.</p> + +<p>JOHNSON, J.B.: Time tests of timber in endwise compression. +Paper before Section D, Am. Assn. for Adv. of Sci., Aug., 1898.</p> + +<p>JOHNSON, WALTER B.: Experiments on the adhesion of iron spikes +of various forms when driven into different species of timbers. +Jour. Franklin Inst., Vol. XIX (n.s.), 1837, pp. 281-292.</p> + +<p>JULIUS, G.A.: Western Australia timber tests, 1906. The physical +characteristics of the hardwoods of Western Australia. Perth, +1906, pp. 36.</p> + +<p>——: Supplement to the Western Australia timber tests, 1906. +The hardwoods of Australia. Perth, 1907, pp. 6.</p> + +<p>KARMARSH, CARL: Handbuch der mechanischen Technologie. I. Aufl., +1837; V. Aufl., 1875; verm. von H. Fisher, 1888.</p> + +<p>KIDDER, F.E.: Experiments on the transverse strength of southern +and white pine. Van Nostrand's Eng. Mag., Vol. XXII, 1880, pp. +166-168.</p> + +<p>——: Experiments on the strength and stiffness of small spruce +beams. <i>Ibid.</i>, Vol. XXIV, 1881, pp. 473-477.</p> + +<p>——: Experiments on the fatigue of small spruce beams. Jour. +Franklin Inst., Vol. CXIV, 1882, pp. 261-279.</p> + +<p>KIDWELL, EDGAR: The efficiency of built-up wooden beams. Trans. +Am. Inst. Min. Eng., Feb., June, 1898.</p> + +<p>KIRKALDY, WM. G.: Illustrations of David Kirkaldy's system of +mechanical testing. London, 1891.</p> + +<p>KUMMER, FREDERICK A.: The effects of preservative treatment on +the strength of timber. Proc. Am. Soc. Test. Mat., Vol. IV, +1904, pp. 434-438.</p> + +<a name="pg153"></a> + +<p>LABORDÈRE, P., and ANSTETT, F.: Contribution to the study of +means for improving the strength of wood for pavements. Proc. +Int. Assn. Test. Mat., 1912, XXIII<sub><small>4</small></sub>, pp. 12.</p> + +<p>LANZA, GAETANO: An account of certain tests on the transverse +strength and stiffness of large spruce beams. Trans. Am. Soc. +Mech. Eng., Vol. IV, 1882, pp. 119-135. See also Jour. Franklin +Inst., Vol. XCV, 1883, pp. 81-94.</p> + +<p>LASLETT, T.: Properties and characteristics of timber. Chatham, +1867.</p> + +<p>——: Timber and timber trees, native and foreign. (2d ed. +revised and enlarged by H. Marshall Ward.) London and New York, +1894.</p> + +<p>LEA, W.: Tables of strength and deflection of timber. London, +1861.</p> + +<p>LEDEBUR, A.: Die Verarbeitung des Holzes auf mechanischem Wege. +1881.</p> + +<p>LORENZ, N. VON: Analytische Untersuchung des Begriffes der +Holzhärte. Centralblatt f. d. ges. Forstwesen, Wien, 1909, pp. +348-387.</p> + +<p>LUDWIG, PAUL: Die Regelprobe. Ein neues Verfahren zur +Härtebestimmung von Materialien. Berlin. 1908.</p> + +<p>MACFARLAND, H.B.: Tests of longleaf pine bridge timbers. Bul. +149, Am. Ry. Eng. Assn., Sept., 1912. See also Eng. News, Dec. +12, 1912, p. 1035.</p> + +<p>McKAY, DONALD: On the weight and strength of American +ship-timber. Jour. Franklin Inst., Vol. XXXIX (3d series), 1860, +p. 322.</p> + +<p>MALETTE, J.: Essais des bois de construction. Revue Technique, +Apr. 25, 1905.</p> + +<p>MANN, JAMES: Australian timber: its strength, durability, and +identification. Melbourne, 1900.</p> + +<p>MARTIN, CLARENCE A.: Tests on the relation between cross-bending +and direct compressive strength in timber. Railroad Gazette, +Mch. 13, 1903.</p> + +<p>Methods of testing metals and alloys ... Recommended by the +Fourth Congress of the International Association for Testing +Materials, held at Brussels, Sept. 3-6, 1906. London, 1907, pp. +54. Methods of testing wood, pp. 39-49.</p> + +<p>MIKOLASCHEK, CARL: Untersuchungen über die Elasticität und +Festigkeit der wichtigsten Bau- und Nutzhölzer. Mitt. a. d. +forstl. Versuchswesen Oesterreiches, II. Bd., 1. Hft., Wien, +1879.</p> + +<p>MOELLER, JOSEPH: Die Rohstoffe des Tischler- und +Drechslergewerbes. I. Theil: Das Holz. Kassel, 1883, pp. 68-122.</p> + +<p>MOLESWORTH, G.L.: Graphic diagrams of strength of teak beams. +Roorke, 1881.</p> + +<a name="pg154"></a> + +<p>MORGAN, J.J.: Bending strength of yellow pine timber. Eng. +Record, Vol. LXVII, 1913, pp. 608-609.</p> + +<p>MOROTO, K.: Untersuchungen über die Biegungselasticität und +-Festigkeit der japanischen Bauhölzer. Centralblatt f. d. ges. +Forstwesen, Wien, 1908, pp. 346-355.</p> + +<p>NORDLINGER, H.: Die technischen Eigenschaften der Hölzer für +Forst- und Baubeamte, Technologen und Gewerbetreibende. +Stuttgart, 1860.</p> + +<p>——: Druckfestigkeit des Holzes. 1882.</p> + +<p>——: Die gewerblichen Eigenschaften der Hölzer. Stuttgart, +1890.</p> + +<p>NORTH, A.T.: The grading of timber on the strength basis. +Address before Western Society of Engineers. Lumber World +Review, May 25, 1914, pp. 27-29.</p> + +<p>NORTON, W.A.: Results of experiments on the set of bars of wood, +iron, and steel, after a transverse stress. Van Nostrand's Eng. +Mag., Vol. XVII, 1877, pp. 531-535.</p> + +<p>PACCINOTTI E PERI: [Investigations into the elasticity of +timbers.] Il Cimento, Vol. LVIII, 1845.</p> + +<p>PALACIO, E.: Tensile tests of timber. La Ingenieria, Buenos +Aires, May 31, 1903, <i>et seq.</i></p> + +<p>PARENT,—: Expériences sur la résistance des bois de chêne et de +sapin. Mémoires de l'Académie des Sciences, 1707-08.</p> + +<p>Propositions relatives à l'établissement d'un precédé uniforme +pour l'essai des qualités techniques des bois. Proc. Int. Assn. +Test. Mat., 1901, Annexe, pp. 13-28.</p> + +<p>ROGERS, CHARLES G.: A manual of forest engineering for India. +Vol. I, Calcutta, 1900, pp. 50-91.</p> + +<p>RUDELOFF, M.: Der heutige Stand der Holzuntersuchungen. Mitt. a. +d. königlichen tech. Versuchsanstalt, Berlin, IV, 1899.</p> + +<p>——: Principles of a standard method of testing wood. Proc. +Int. Assn. Test. Mat., 1906, 23 C, pp. 16.</p> + +<p>——: Large <i>vs.</i> small test-pieces in testing wood. Proc. Int. +Soc. Test. Mat., 1912, XXIII<sub><small>1</small></sub>, pp. 7.</p> + +<p>SARGENT, CHARLES SPRAGUE: Woods of the United States, with an +account of their structure, qualities, and uses. New York, 1885.</p> + +<p>SCHNEIDER, A.: Zusammengesetzte Träger. Zeitschrift d. Oesterr. +Ing. u. Arch. Ver., Nov. 24; Dec. 9, 1899.</p> + +<p>SCHWAPPACH, A.F.: Beiträge zur Kenntniss der Qualität des +Rotbuchenholzes. Zeitschrift f. Forst- und Jagdwesen, Berlin, +1894, pp. 513-539.</p> + +<p>——: Untersuchungen über Raumgewicht und Druckfestigkeit des +Holzes wichtiger Waldbäume. Berlin, 1897-98.</p> + +<p>——: Etablissement de méthodes uniformes pour l'essai <a name="pg155"></a> á la +compression des bois. Proc. Int. Assn. Test. Mat., 1901, Rapport +23, pp. 28.</p> + +<p>SEBERT, H.: Notice sur les bois de la Nouvelle Calédonie suivie +de considerations génerates sur les propriétés mécaniques des +bois et sur les precédés employés pour les mesurer. Paris.</p> + +<p>SHERMAN, EDWARD C.: Crushing tests on water-soaked timbers. Eng. +News, Vol. LXII, 1909, p. 22.</p> + +<p>SNOW, CHARLES H.: The principal species of wood: their +characteristic properties. New York, 1908.</p> + +<p>STAUFFER, OTTMAR: Untersuchungen über specifisches +Trockengewicht, sowie anatomisches Verhalten des Holzes der +Birke. München, 1892.</p> + +<p>STENS, D.: Ueber die Eigenschaftenimprägnierter Grubenholzer, +insbesondere über ihre Festigkeit. Glückauf, Essen, Mch. 6, +1907.</p> + +<p>Strength of wood for pavements. Can. Eng., Toronto, Sept. 12, +1912.</p> + +<p>STÜBSCHEN-KISCHNER: Karmarsch-Heerins technisches Wröterbuch. 3. +Aufl., 1886.</p> + +<p>TALBOT, ARTHUR N.: Tests of timber beams. Bul. 41, Eng. Exp. +Sta., Univ. of Ill., Urbana, 1910.</p> + +<p>Tests of wooden beams made at the Massachusetts Institute of +Technology on spruce, white pine, yellow pine, and oak beams of +commercial sizes. Technology Quarterly, Boston, Vol. VII, 1894.</p> + +<p>TETMAJER, L. v.: Zur Frage der Knickungsfestigkeit der +Bauhölzer. Schweizerische Bauzeitung, Bd. 11, Nr. 17.</p> + +<p>——: Methoden und Resultate der Prüfung der schweizerischen +Bauhölzer. Mitt. d. Anstalt z. Prüfung v. Baumaterialien am +eidgenössischen Polytechnicum in Zürich. 2. Hft., 1884.</p> + +<p>——: Methoden und Resultate der Prüfung der schweizerischen +Bauhölzer. Mitt. d. Materialprüfungs-Anstalt am Schweiz. +Polytechnikum in Zürich. Landesaustellungs-Ausgabe, 2. Hft., +Zürich, 1896.</p> + +<p>THELEN, ROLF: The structural timbers of the Pacific Coast. +Proc. Am. Soc. Test. Mat., Vol. VIII, 1908, pp. 558-567.</p> + +<p>THURSTON, R.H.: Torsional resistance of materials determined by +a new apparatus with automatic registry. Jour. Franklin Inst., +Vol. LXV, 1873, pp. 254-260.</p> + +<p>——: On the strength of American timber. <i>Ibid.</i>, Vol. LXXVIII, +1879, pp. 217-235.</p> + +<p>——: Experiments on the strength of yellow pine. <i>Ibid.</i>, Vol. +LXXIX, 1880, pp. 157-163.</p> + +<p>——: Influence of time on bending strength and elasticity. +Proc. Am. Assn. for Adv. Sci., 1881. Also Proc. Inst. C.E., Vol. +LXXI.</p> + +<p>——: On the effect of prolonged stress upon the strength <a name="pg156"></a> and +elasticity of pine timber. Jour. Franklin Inst., Vol. LXXX, +1881, pp. 161-169.</p> + +<p>THURSTON, R.H.: On Flint's investigations of +Nicaraguan woods. <i>Ibid.</i>, Vol. XCIV, 1887, pp. 289-315.</p> + +<p>TIEMANN, HARRY DONALD: The effect of moisture and other +extrinsic factors upon the strength of wood. Proc. Am. Soc. +Test. Mat., Vol. VII, 1907, pp. 582-594.</p> + +<p>——: The effect of the speed of testing upon the strength of +wood and the standardization of tests for speed. <i>Ibid.</i>, Vol. +VIII, 1908, pp. 541-557.</p> + +<p>——: The theory of impact and its application to testing +materials. Jour. Franklin Inst., Vol. CLXVIII, 1909, pp. +235-259; 336-364.</p> + +<p>——: Some results of dead load bending tests of timber by means +of a recording deflectometer. Proc. Am. Soc. Test. Mat., Vol. +IX, 1909, pp. 534-548.</p> + +<p>TJADEN, M.E.H.: Het Indrukken van Paalkoppen in Kespen. De +Ingenieur, Sept. 11, 1909.</p> + +<p>——: Weerstand van Hout loodrecht op de Vezelrichting. <i>Ibid.</i>, +May, 1911.</p> + +<p>——: Buigvastheid van Hout. <i>Ibid.</i>, May 31, 1913.</p> + +<p>TRAUTWINE, JOHN C.: Shearing strength of some American woods. +Jour. Franklin Inst., Vol. CIX, 1880, pp. 105-106.</p> + +<p>TREDGOLD, THOMAS: Elementary principles of carpentry. London, +1870.</p> + +<p>TURNBULL, W.: A practical treatise on the strength and stiffness +of timber. London, 1833.</p> + +<p>Untersuchungen über den Einfluss des Blauwerdens auf die +Festigkeit von Kiefernholz. Mitt. a. d. könig. techn. +Versuchsanstalten, I, 1897.</p> + +<p>Verfahren zur Prüfung v. Metallen und Legierungen, von +hydraulischen Bindemitteln, von Holz, von Ton-, Steinzeug- und +Zementröhren. Empfohlen v. dem in Brüssel v. 3-6, IX, 1906, +abgeh. IV. Kongress des internationalen Verbandes f. die +Materialprüfungen der Technik. Wien, 1907.</p> + +<p>WARREN, W.H.: Australian timbers. Sydney, 1892.</p> + +<p>——: The strength, elasticity, and other properties of New +South Wales hardwood timbers. Sydney, 1911.</p> + +<p>——: The strength, elasticity, and other properties of New +South Wales hardwood timbers. Proc. Int. Assn. Test. Mat., 1912, +XXIII<sub><small>6</small></sub>, pp. 9.</p> + +<p>——: The properties of New South Wales hardwood timbers. +Builder, London, Nov. 1, 1912.</p> + +<p>——: The hardwood timbers of New South Wales, Australia. Jour. +Soc. of Arts, London, Dec. 6, 1912.</p> + +<a name="pg157"></a> + +<p>WELLINGTON, A.M.: Experiments on impregnated timber. Railroad +Gazette, 1880.</p> + +<p>WIJKANDER, ——: Untersuchung der Festigkeitseigenschaften +schwedischer Holzarten in der Materialprüfungsanstalt des +Chalmers'schen Institutes ausgeführt. 1897.</p> + +<p>WING, CHARLES B.: Transverse strength of the Douglas fir. Eng. +News, Vol. XXXIII, Mch. 14, 1895.</p> + +<a name="BIB_III"></a> +<h3>PART III.<br>PUBLICATIONS OF THE U.S. GOVERNMENT ON THE MECHANICAL PROPERTIES OF WOOD, AND TIMBER TESTING</h3> + +<h4>MISCELLANEOUS</h4> + +<p>House Misc. Doc. 42, pt. 9, 47th Cong., 2d sess., 1884. (Vol. +IX, Tenth Census report.) Report on the forests of North America +(exclusive of Mexico). Part II, The Woods of the United States.</p> + +<p>House Report No. 1442, 53d Cong., 2d sess. Investigations and +tests of American timber. 1894, pp. 4.</p> + +<p>War Dept. Doc. 1. Resolutions of the conventions held at Munich, +Dresden, Berlin, and Vienna, for the purpose of adopting uniform +methods for testing construction materials with regard to their +mechanical properties. By J. Bauschinger. Translated by O.M. +Carter and E.A. Gieseler. 1896, pp. 44.</p> + +<p>War Dept. Doc. 11. On tests of construction materials. +Translations from the French and from the German. By O.M. Carter +and E.A. Gieseler. 1896, pp. 84.</p> + +<p>House Doc. No. 181, 55th Cong., 3d sess. Report upon the +forestry investigations of the U.S. Department of Agriculture, +1877-1898. By B.E. Fernow, 1899, pp. 401. Contains chapter on +The work in timber physics in the Division of Forestry, by +Filibert Roth, pp. 330-395. +<h4>FOREST SERVICE</h4> +<p>Cir. 7—The Government timber tests [189-], pp. 4.</p> + +<p>Cir. 8—Strength of "boxed" or "turpentine" timber. 1892, pp. 4.</p> + +<p>Bul. 6—Timber Physics. Pt. I. Preliminary report. 1. Need of +the investigation. 2. Scope and historical development of the +science of "timber physics." 3. Organization and methods of +timber examinations in the Division of Forestry. By B.E. Fernow, +1892, pp. 57.</p> + +<p>Unnumbered Cir.—Instructions for the collection of test pieces +of pines for timber investigations [1893], pp. 4.</p> + +<a name="pg158"></a> + +<p>Cir. 9—Effect of turpentine gathering on the timber of longleaf +pine. By B.E. Fernow [1893], p. 1.</p> + +<p>Bul. 8—Timber physics. Pt. II. Progress report. Results of +investigations on longleaf pine. 1893, pp. 92.</p> + +<p>Bul. 10—Timber: an elementary discussion of the characteristics +and properties of wood. By Filibert Roth. 1895, pp. 88.</p> + +<p>Bul. 12—Economical designing of timber trestle bridges. By A.L. +Johnson, 1896, pp. 57.</p> + +<p>Cir. 12—Southern pine, mechanical and physical properties. +1896, pp. 12.</p> + +<p>Cir. 15—Summary of mechanical tests on thirty-two species of +American woods. 1897, pp. 12.</p> + +<p>Cir. 18—Progress in timber physics. 1898, pp. 20.</p> + +<p>Cir. 19—Progress in timber physics: Bald cypress (<i>Taxodium +distichum</i>). By Filibert Roth, 1898, pp. 24.</p> + +<p>Y.B. Extr. 288—Tests on the physical properties of woods. By +F.E. Olmstead, 1902, pp. 533-538.</p> + +<p>Unnumbered Cir.—Timber tests. [1903], pp. 15.</p> + +<p>Unnumbered Cir.—Timber preservation and timber testing at the +Louisiana Purchase Exposition. 1904, pp. 6.</p> + +<p>Cir. 32—Progress report on the strength of structural timber. +By W.K. Hatt, 1904, pp. 28.</p> + +<p>Bul. 58—The red gum. By Alfred Chittenden. Includes a +discussion of The mechanical properties of red gum wood, by W.K. +Hatt. 1905, pp. 56.</p> + +<p>Cir. 38—Instructions to engineers of timber tests. By W.K. +Hatt, 1906, pp. 55. Revised edition, 1909, pp. 56.</p> + +<p>Cir. 39—Experiments on the strength of treated timber. By W.K. +Hatt, 1906, pp. 31. Revised edition, 1908.</p> + +<p>Bul. 70—Effect of moisture upon the strength and stiffness of +wood. By H.D. Tiemann, 1906, pp. 144.</p> + +<p>Cir. 46—Holding force of railroad spikes in wooden ties. By +W.K. Hatt, 1906, pp. 7.</p> + +<p>Cir. 47—Strength of packing boxes of various woods. By W.K. +Hatt, 1906, pp. 7.</p> + +<p>Cir. 108—The strength of wood as influenced by moisture. By +H.D. Tiemann, 1907, pp. 42.</p> + +<p>Cir. 115—Second progress report on the strength of structural +timber. By W.K. Hatt, 1907, pp. 39.</p> + +<p>Cir. 142—Tests of vehicle and implement woods. By H.B. Holroyd +and H.S. Betts, 1908, pp. 29.</p> + +<p>Cir. 146—Experiments with railway cross-ties. By H.B. Eastman, +1908, pp. 32.</p> + +<p>Cir. 179—Utilization of California eucalypts. By H.S. Betts and +C. Stowell Smith, 1910, pp. 30.</p> + +<a name="pg159"></a> + +<p>Bul. 75—California tanbark oak. Part II, Utilization of the +wood of tanbark oak, by H.S. Betts, 1911, pp. 24-32.</p> + +<p>Bul. 88—Properties and uses of Douglas fir. By McGarvey Cline +and J.B. Knapp, 1911, pp. 75.</p> + +<p>Cir. 189—Strength values for structural timbers. By McGarvey +Cline, 1912, pp. 8.</p> + +<p>Cir. 193—Mechanical properties of redwood. By A.L. Heim, 1912, +pp. 32.</p> + +<p>Bul. 108—Tests of structural timbers. By McGarvey Cline and +A.L. Heim, 1912, pp. 1231.</p> + +<p>Bul. 112—Fire-killed Douglas fir: a study of its rate of +deterioration, usability, and strength. By J.B. Knapp, 1912, pp. +18.</p> + +<p>Bul. 115—Mechanical properties of western hemlock. By O.P.M. +Goss, 1913, pp. 45.</p> + +<p>Bul. 122—Mechanical properties of western larch. By O.P.M. +Goss, 1913, pp. 45.</p> + +<p>Cir. 213—Mechanical properties of woods grown in the United +States. 1913, pp. 4.</p> + +<p>Cir. 214—Tests of packing boxes of various forms. By John A. +Newlin, 1913, pp. 23.</p> + +<p>Review Forest Service Investigations. 1913. [Outline of +investigations.] Vol. I, pp. 17-21. A microscopic study of the +mechanical failure of wood, by Warren D. Brush. Vol. II, pp. +33-38.</p> + +<p>Bul. 67, U.S.D.A.—Tests of Rocky Mountain woods for telephone +poles. By Norman deW. Betts and A.L. Heim, 1914, pp. 28.</p> + +<p>Bul. 77, U.S.D.A.—Rocky Mountain mine timbers. By Norman deW. +Betts, 1914, pp. 34.</p> + +<p>Bul. 86, U.S.D.A.—Tests of wooden barrels. By J.A. Newlin, +1914, pp. 12. +<h4>REPORTS OF TESTS ON THE STRENGTH OF STRUCTURAL MATERIAL, MADE AT THE WATERTOWN ARSENAL, MASS.</h4> +<p>House Ex. Doc. No. 12, 47th Cong., 1st sess., 1882. Strength of +wood grown on the Pacific slope, pp. 19-93.</p> + +<p>Senate Ex. Doc. No. 1, 47th Cong., 2d sess., 1883. Resistance of +white and yellow pines to forces of compression in the direction +of the fibers, as used for columns, or posts, pp. 239-395.</p> + +<p>Senate Ex. Doc. No. 5, 48th Cong., 1st sess., 1884. Tests of +California laurel wood by compression, indentation, shearing, +transverse tension, pp. 223-236. Tests of North American woods +(under supervision of Prof. C.S. Sargent in charge of the +forestry division of the Tenth Census), with 16 photographs of +fractures of American woods, pp. 237-347.</p> + +<a name="pg160"></a> + +<p>Senate Ex. Doc. No. 35, 49th Cong., 1st sess., 1885. Adhesion of +nails, spikes, and screws in various woods. Experiments on the +resistance of cut nails, wire nails (steel), wood screws, lag +screws in white pine, yellow pine, chestnut, white oak, and +laurel, pp. 448-471.</p> + +<p>House Ex. Doc. No. 14, 51st Cong., 1st sess., 1890. Adhesion of +spikes and bolts in railroad ties, pp. 595-617.</p> + +<p>House Ex. Doc. No. 161, 52d Cong., 1st sess., 1892. Adhesion of +nails in wood, pp. 744-745.</p> + +<p>House Ex. Doc. No. 92, 53d Cong., 3d sess., 1895. +Woods—compression tests (endwise compression), pp. 471-476.</p> + +<p>House Doc. No. 54, 54th Cong., 1st sess., 1896. Compression +tests on Douglas fir wood, pp. 536-563. Expansion and +contraction of oak and pine wood, pp. 567-574.</p> + +<p>House Doc. No. 164, 55th Cong., 2d sess., 1898. Compression +tests of timber posts, pp. 405-411. New posts of yellow pine and +spruce, pp. 413-450; Old yellow pine posts from Boston Fire +Brick Co. building, No. 394 Federal St., Boston, Mass., pp. +451-473.</p> + +<p>House Doc. No. 143, 55th Cong., 3d sess., 1899. Fire-proofed +wood (endwise and transverse tests), pp. 676-681.</p> + +<p>House Doc. No. 190, 56th Cong., 2d sess., 1901. Cypress wood for +United States Engineer Corps; compression and transverse tests, +pp. 1121-1126. Old white pine and red oak from roof trusses of +Old South Church, Boston, Mass., pp. 1127-1130. Compression of +rubber, balata, and wood buffers, pp. 1149-1158.</p> + +<p>House Doc. No. 335, 57th Cong., 2d sess., 1903. Douglas fir and +white oak woods. Transverse and shearing tests; also +observations on heat conductivity of sticks over wood fires and +a stick exposed to low temperature. Expansion crosswise the +grain of wood after submersion, pp. 519-561. Adhesion of lag +screws and bolts in wood, pp. 563-578.</p> + +<a name="pg161"></a> +<a name="INDEX"></a><h2>INDEX</h2> + +<a name="Abrasion"></a> +<p>Abrasion, + <a href="#pg039">39</a>, + <a href="#pg114">114</a>-117 +</p> + +<p>Annual rings, + <a href="#pg044">44</a> +</p> + +<p>Apparatus, testing, + <a href="#pg094">94</a>, + <a href="#pg099">99</a>, + <a href="#pg102">102</a>, + <a href="#pg104">104</a>, + <a href="#pg107">107</a>, + <a href="#pg110">110</a>-111, + <a href="#pg114">114</a>, + <a href="#pg117">117</a>, + <a href="#pg118">118</a>, + <a href="#pg121">121</a>, + <a href="#pg122">122</a>, + <a href="#pg132">132</a>, + <a href="#pg133">133</a>, + <a href="#pg136">136</a> +</p> + +<p>Arborvitæ, + <a href="#pg006">6</a>, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg042">42</a>, + <a href="#pg057">57</a> +</p> + +<p>Ash, + <a href="#pg015">15</a>, + <a href="#pg022">22</a>, + <a href="#pg044">44</a>, + <a href="#pg048">48</a>, + <a href="#pg051">51</a>, + <a href="#pg066">66</a>, + <a href="#pg078">78</a> +</p> +<p class="ind">black, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg056">56</a> +</p> +<p class="ind">white, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg045">45</a>, + <a href="#pg056">56</a> +</p> + +<p>Aspen, largetooth, + <a href="#pg013">13</a> +</p> + +<p>Axis, neutral, + <a href="#pg023">23</a> +</p> + +<p>Basswood, + <a href="#pg009">6</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg044">44</a>, + <a href="#pg056">56</a> +</p> + +<p>Beams, + <a href="#pg015">15</a>, + <a href="#pg024">24</a>-37, + <a href="#pg092">92</a>, + <a href="#pg094">94</a> +</p> +<p class="ind">cantilever, + <a href="#pg024">24</a> +</p> +<p class="ind">continuous, + <a href="#pg024">24</a> +</p> +<p class="ind">simple, + <a href="#pg024">24</a> +</p> + +<p>Beech, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg022">22</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg051">51</a>, + <a href="#pg057">57</a> +</p> + +<p>Bending large beams, + <a href="#pg094">94</a>-99 +</p> +<p class="ind">small beams, + <a href="#pg099">99</a>-102, + <a href="#pg132">132</a> +</p> +<p class="ind">strength, + <a href="#pg002">2</a>, + <a href="#pg022">22</a>-37, + <a href="#pg026">26</a>, + <a href="#pg075">75</a> +</p> + +<p>Bibliography, + <a href="#pg145">145</a>-160 +</p> + +<p>Birch, + <a href="#pg022">22</a>, + <a href="#pg044">44</a> +</p> +<p class="ind">yellow, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg057">57</a> +</p> + +<p>Bird-peck, + <a href="#pg059">59</a>, + <a href="#pg072">72</a> +</p> + +<p>Black check, + <a href="#pg059">59</a> +</p> + +<p>Boiling, effect of, + <a href="#pg006">6</a>, + <a href="#pg085">85</a> +</p> + +<p>Bow, flexure of a, + <a href="#pg004">4</a> +</p> + +<p>Boxheart, + <a href="#pg054">54</a>, + <a href="#pg082">82</a> +</p> + +<p>Brash, + <a href="#pg006">6</a> +</p> + +<p>Breaking strength of beams, + <a href="#pg015">15</a> +</p> + +<p>Brittleness, + <a href="#pg006">6</a>, + <a href="#pg034">34</a>, + <a href="#pg037">37</a>, + <a href="#pg038">38</a> +</p> + +<p>Buckeye, + <a href="#pg013">13</a>, + <a href="#pg044">44</a> +</p> + +<p>Buckling of fibres, + <a href="#pg015">15</a>, + <a href="#pg077">77</a> +</p> + +<p>Butternut, + <a href="#pg013">13</a> +</p> + +<p>Cantilever, + <a href="#pg024">24</a> +</p> + +<p>Calibration of testing machines, + <a href="#pg092">92</a>, + <a href="#pg112">112</a> +</p> + +<p>Case-hardening, + <a href="#pg080">80</a> +</p> + +<p>Catalpa, + <a href="#pg044">44</a> +</p> + +<p>Cedar, Central American, + <a href="#pg022">22</a> +</p> +<p class="ind">incense, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg057">57</a> +</p> +<p class="ind">red, + <a href="#pg144">144</a> +</p> +<p class="ind">white, + <a href="#pg022">22</a> +</p> + +<p>Checking, + <a href="#pg054">54</a>, + <a href="#pg061">61</a>, + <a href="#pg074">74</a>, + <a href="#pg075">75</a>-84 +</p> + +<p><i>Chelura</i>, + <a href="#pg067">67</a> +</p> + +<p>Cherry, black, + <a href="#pg013">13</a>, + <a href="#pg022">22</a> +</p> + +<p>Chestnut, + <a href="#pg015">15</a>, + <a href="#pg022">22</a>, + <a href="#pg044">44</a>, + <a href="#pg049">49</a>, + <a href="#pg050">50</a>, + <a href="#pg051">51</a>, + <a href="#pg066">66</a>, + <a href="#pg078">78</a> +</p> + +<p>Cleavability, + <a href="#pg002">2</a>, + <a href="#pg041">41</a> +</p> + +<p>Cleavage, + <a href="#pg041">41</a>, + <a href="#pg118">118</a>, + <a href="#pg133">133</a> +</p> + +<p>Coefficient of elasticity (see <a href="#Modulus_of_elasticity">Modulus of elasticity</a>) +</p> +<p class="ind">expansion, + <a href="#pg084">84</a> +</p> + +<p>Cold, effect of, + <a href="#pg086">86</a> +</p> + +<p>Color, + <a href="#pg050">50</a>, + <a href="#pg058">58</a>-59 +</p> + +<p>Column, long, + <a href="#pg012">12</a>, + <a href="#pg014">14</a>, + <a href="#pg144">144</a> +</p> +<p class="ind">short, + <a href="#pg015">15</a>, + <a href="#pg102">102</a>-104 +</p> + +<p>Compression across the grain, + <a href="#pg094">94</a>, + <a href="#pg104">104</a>-107, + <a href="#pg133">133</a> +</p> +<a name="C_endwise"></a> +<p class="ind">endwise, + <a href="#pg012">12</a>, + <a href="#pg092">92</a>, + <a href="#pg094">94</a>, + <a href="#pg102">102</a>, + <a href="#pg132">132</a> +</p> +<p class="ind">failure, + <a href="#pg034">34</a>, + <a href="#pg104">104</a> +</p> +<p class="ind">parallel to grain (<a href="#C_endwise">see C. endwise</a>) +</p> +<p class="ind">perpendicular to grain (<a href="#C_right_angles_to_grain">see C. right angles to grain</a>)</p> +<a name=C_right_angles_to_grain></a> +<p class="ind">right angles to grain, + <a href="#pg094">94</a>, + <a href="#pg133">133</a> +</p> + +<p>Compressive strength, + <a href="#pg001">1</a>, + <a href="#pg009">9</a>, + <a href="#pg023">23</a> +</p> + +<p>Compressometer, + <a href="#pg103">103</a> +</p> + +<p>Coniferous wood, + <a href="#pg044">44</a> +</p> + +<p>Cottonwood, + <a href="#pg044">44</a>, + <a href="#pg045">45</a> +</p> + +<p>Creosote, effect of, + <a href="#pg087">87</a> +</p> + +<p>Cross-arms, testing, + <a href="#pg124">124</a> +</p> + +<p>Cross grain, + <a href="#pg008">8</a>, + <a href="#pg059">59</a>-61 +</p> + +<p>Cross-grained tension failure, + <a href="#pg034">34</a> +</p> + +<p>Crushing strength, + <a href="#pg002">2</a>, + <a href="#pg009">9</a>, + <a href="#pg054">54</a>, + <a href="#pg075">75</a> +</p> +<p class="ind">formula for, + <a href="#pg104">104</a> +</p> + +<p>Cucumber tree, + <a href="#pg013">13</a> +</p> + +<p>Cup shake, + <a href="#pg064">64</a> +</p> + +<p>Cypress, bald, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg057">57</a>, + <a href="#pg068">68</a>, + <a href="#pg144">144</a> +</p> + +<p> +Dead Load (<a href="#Load">see Load</a>) +</p> + +<p>Definitions, + <a href="#pg002">2</a>-7 +</p> + +<p>Deflection, + <a href="#pg025">25</a>, + <a href="#pg030">30</a> +</p> +<p class="ind">measuring, + <a href="#pg096">96</a>-97, + <a href="#pg100">100</a> +</p> + +<p>Deflectometer, + <a href="#pg099">99</a>, + <a href="#pg106">106</a>-107 +</p> + +<p>Deformation, measuring, + <a href="#pg103">103</a>, + <a href="#pg107">107</a> +</p> + +<p>Density, + <a href="#pg054">54</a>-58 +</p> + +<p>Diffuse-porous, + <a href="#pg044">44</a>, + <a href="#pg050">50</a> +</p> + +<p>Dogwood, + <a href="#pg022">22</a> +</p> + +<p>Drying, + <a href="#pg075">75</a>-84 +</p> +<p class="ind">effect of, + <a href="#pg075">75</a>-78, + <a href="#pg138">138</a>-139 +</p> + +<p>Dry rot, + <a href="#pg069">69</a> +</p> + +<p>Durability, + <a href="#pg053">53</a>, + <a href="#pg054">54</a>, + <a href="#pg075">75</a> +</p> + +<a name="Early_wood"></a> +<p>Early Wood, + <a href="#pg044">44</a>, + <a href="#pg082">82</a> +</p> + +<p>Ease of working, factors affecting, + <a href="#pg048">48</a>, + <a href="#pg050">50</a> +</p> + +<p>Ebony, + <a href="#pg022">22</a> +</p> + +<p>Elasticity, modulus of, + <a href="#pg006">6</a>, + <a href="#pg025">25</a>, + <a href="#pg089">89</a> +</p> +<p class="ind">formulæ for, + <a href="#pg098">98</a>, + <a href="#pg102">102</a>, + <a href="#pg104">104</a>, + <a href="#pg114">114</a>, + <a href="#pg123">123</a> +</p> + +<p>Elastic limit, + <a href="#pg002">2</a>, + <a href="#pg005">5</a>, + <a href="#pg022">22</a>, + <a href="#pg062">62</a> +</p> +<p class="ind">resilience, + <a href="#pg006">6</a> +</p> +<p class="ind2">formulæ for, + <a href="#pg098">98</a>, + <a href="#pg102">102</a>, + <a href="#pg104">104</a> +</p> + +<p>Elm, + <a href="#pg008">8</a>, + <a href="#pg038">38</a>, + <a href="#pg044">44</a> +</p> +<p class="ind">rock, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg056">56</a> +</p> +<p class="ind">slippery, + <a href="#pg013">13</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg056">56</a> +</p> +<p class="ind">white, + <a href="#pg013">13</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg056">56</a> +</p> + +<p>Elongation, + <a href="#pg003">3</a>, + <a href="#pg007">7</a>, + <a href="#pg033">33</a> +</p> + +<p><i>Eucalyptus globulus</i>, + <a href="#pg054">54</a>, + <a href="#pg078">78</a>, + <a href="#pg082">82</a> +</p> +<p class="ind"><i>viminalis</i>, + <a href="#pg054">54</a> +</p> + +<p>Factor of Safety, + <a href="#pg029">29</a>, + <a href="#pg139">139</a> +</p> + +<p>Failures, bending, + <a href="#pg033">33</a>-37, + <a href="#pg077">77</a>, + <a href="#pg078">78</a> +</p> +<p class="ind">compression, endwise, + <a href="#pg012">12</a>, + <a href="#pg015">15</a>-19, + <a href="#pg104">104</a> +</p> +<p class="ind">cross-grained, + <a href="#pg010">10</a>, + <a href="#pg076">76</a>, + <a href="#pg077">77</a>, + <a href="#pg107">107</a> +</p> +<p class="ind">shearing, + <a href="#pg019">19</a> +</p> +<p class="ind">tension, + <a href="#pg008">8</a> +</p> +<p class="ind">torsion, + <a href="#pg038">38</a>, + <a href="#pg039">39</a> +</p> + +<p>Fibre-saturation point, + <a href="#pg078">78</a> +</p> + +<p>Fibre strain, rate of, + <a href="#pg092">92</a>-93 +</p> +<p class="ind">stress, + <a href="#pg015">15</a> +</p> +<p class="ind2">at elastic limit, + <a href="#pg054">54</a>, + <a href="#pg062">62</a>, + <a href="#pg075">75</a>, + <a href="#pg123">123</a> +</p> +<p class="ind3">formulæ, + <a href="#pg098">98</a>, + <a href="#pg102">102</a>, + <a href="#pg104">104</a>, + <a href="#pg107">107</a>, + <a href="#pg114">114</a> +</p> + +<p>Fir, Alpine, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg057">57</a> +</p> +<p class="ind">amabilis, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg057">57</a> +</p> +<p class="ind">Douglas, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg036">36</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg048">48</a>, + <a href="#pg055">55</a>, + <a href="#pg057">57</a>, + <a href="#pg124">124</a>, + <a href="#pg140">140</a>, + <a href="#pg141">141</a>, + <a href="#pg142">142</a>, + <a href="#pg143">143</a>, + <a href="#pg144">144</a> +</p> +<p class="ind">white, + <a href="#pg009">9</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg057">57</a> +</p> + +<p>Flexibility, + <a href="#pg005">5</a>, + <a href="#pg037">37</a> +</p> + +<p>Flexure, + <a href="#pg004">4</a>, + <a href="#pg012">12</a>, + <a href="#pg060">60</a> +</p> + +<p>Formulæ, + <a href="#pg098">98</a>, + <a href="#pg102">102</a>, + <a href="#pg104">104</a>, + <a href="#pg107">107</a>, + <a href="#pg110">110</a>, + <a href="#pg114">114</a>, + <a href="#pg123">123</a> +</p> + +<p>Frost splits, + <a href="#pg062">62</a>-64 +</p> + +<p>Fungi 59, + <a href="#pg068">68</a>-70, + <a href="#pg075">75</a> +</p> + +<p>Grain, cross, + <a href="#pg008">8</a>, + <a href="#pg059">59</a>-61 +</p> +<p class="ind">diagonal, + <a href="#pg060">60</a> +</p> +<p class="ind">spiral, + <a href="#pg060">60</a> +</p> + +<p>Growth, in diameter, + <a href="#pg043">43</a>, + <a href="#pg044">44</a> +</p> +<p class="ind">locality of, effect, + <a href="#pg070">70</a>-73 +</p> +<p class="ind">rate of, effect, + <a href="#pg043">43</a>, + <a href="#pg050">50</a>, + <a href="#pg072">72</a> +</p> +<p class="ind">rings, + <a href="#pg044">44</a>, + <a href="#pg052">52</a> +</p> +<p class="ind2">measuring, + <a href="#pg095">95</a>-96 +</p> + +<p>Gum 22, + <a href="#pg044">44</a>, + <a href="#pg051">51</a> +</p> +<p class="ind">red, + <a href="#pg027">27</a>, + <a href="#pg045">45</a>, + <a href="#pg056">56</a> +</p> + +<p>Hackberry, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg042">42</a>, + <a href="#pg051">51</a>, + <a href="#pg056">56</a> +</p> + +<p>Hardness, + <a href="#pg002">2</a>, + <a href="#pg039">39</a>-41, + <a href="#pg054">54</a>, + <a href="#pg114">114</a>-118, + <a href="#pg133">133</a> +</p> + +<p>Heart break, + <a href="#pg065">65</a> +</p> +<p class="ind">shake, + <a href="#pg064">64</a> +</p> + +<p>Heartwood, + <a href="#pg050">50</a>-54, + <a href="#pg058">58</a>, + <a href="#pg073">73</a>, + <a href="#pg075">75</a> +</p> + +<p>Heat, effect of, + <a href="#pg084">84</a>-86 +</p> + +<p>Hemlock, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg015">15</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg022">22</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg044">44</a>, + <a href="#pg045">45</a>, + <a href="#pg056">56</a>, + <a href="#pg078">78</a> +</p> +<p class="ind">western, + <a href="#pg048">48</a>, + <a href="#pg059">59</a>, + <a href="#pg140">140</a>, + <a href="#pg141">141</a>, + <a href="#pg142">142</a>, + <a href="#pg143">143</a>, + <a href="#pg144">144</a> +</p> + +<p>Hickory, + <a href="#pg008">8</a>, + <a href="#pg022">22</a>, + <a href="#pg038">38</a>, + <a href="#pg040">40</a>, + <a href="#pg043">43</a>, + <a href="#pg044">44</a>, + <a href="#pg049">49</a>, + <a href="#pg051">51</a>, + <a href="#pg053">53</a>, + <a href="#pg055">55</a>, + <a href="#pg059">59</a>, + <a href="#pg065">65</a>, + <a href="#pg066">66</a>, + <a href="#pg072">72</a>, + <a href="#pg124">124</a> +</p> +<p class="ind">big shellbark, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg056">56</a> +</p> +<p class="ind">bitternut, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg056">56</a> +</p> +<p class="ind">mockernut, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg056">56</a> +</p> +<p class="ind">nutmeg, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg056">56</a> +</p> +<p class="ind">pignut, + <a href="#pg006">6</a>, + <a href="#pg007">7</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg048">48</a>, + <a href="#pg056">56</a> +</p> +<p class="ind">shagbark, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg056">56</a> +</p> +<p class="ind">water, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg056">56</a> +</p> + +<p>Hollow-horning, + <a href="#pg080">80</a> +</p> + +<p>Honey-combing, + <a href="#pg054">54</a>, + <a href="#pg080">80</a> +</p> + +<p>Impact, + <a href="#pg030">30</a>-33, + <a href="#pg110">110</a>-114, + <a href="#pg132">132</a> +</p> + +<p>Implement woods, testing, + <a href="#pg124">124</a> +</p> + +<p>Indentation, + <a href="#pg039">39</a>, + <a href="#pg117">117</a>-118 +</p> + +<p>Injuries, fungous, + <a href="#pg052">52</a>, + <a href="#pg059">59</a>, + <a href="#pg068">68</a>-70 +</p> +<p class="ind">insect, + <a href="#pg052">52</a>, + <a href="#pg066">66</a>-67, + <a href="#pg072">72</a> +</p> +<p class="ind">marine wood-borer, + <a href="#pg067">67</a>-68 +</p> +<p class="ind">parasitic plant, + <a href="#pg070">70</a> +</p> + +<p>Kerosene, effect of, + <a href="#pg087">87</a> +</p> + +<p>Knots, + <a href="#pg051">51</a>, + <a href="#pg052">52</a>, + <a href="#pg061">61</a>-62, + <a href="#pg089">89</a> +</p> + +<p>Larch, + <a href="#pg008">8</a> +</p> +<p class="ind">western, + <a href="#pg036">36</a>, + <a href="#pg048">48</a>, + <a href="#pg064">64</a>, + <a href="#pg140">140</a>, + <a href="#pg141">141</a>, + <a href="#pg142">142</a>, + <a href="#pg143">143</a> +</p> + +<a name="Late_wood"></a> +<p>Late wood, + <a href="#pg044">44</a>, + <a href="#pg059">59</a>, + <a href="#pg082">82</a> +</p> +<p class="ind">measuring, + <a href="#pg096">96</a> +</p> +<p class="ind">relation to strength, + <a href="#pg047">47</a>-49 +</p> + +<p>Limit of elasticity, + <a href="#pg005">5</a> +</p> + +<p><i>Limnoria</i>, + <a href="#pg067">67</a> +</p> + +<p>Live load, + <a href="#pg028">28</a> +</p> +<a name="Load"></a> +<p>Load, application of, + <a href="#pg029">29</a> +</p> +<p class="ind">concentrated, + <a href="#pg028">28</a> +</p> +<p class="ind">dead, + <a href="#pg028">28</a>, + <a href="#pg144">144</a> +</p> +<p class="ind">immediate, + <a href="#pg028">28</a> +</p> +<p class="ind">kinds of, + <a href="#pg026">26</a> +</p> +<p class="ind">live, + <a href="#pg028">28</a> +</p> +<p class="ind">maximum, + <a href="#pg029">29</a> +</p> +<p class="ind">permanent, + <a href="#pg028">28</a> +</p> +<p class="ind">safe, + <a href="#pg029">29</a> +</p> +<p class="ind">uniform, + <a href="#pg026">26</a> +</p> + +<p>Loading, centre, + <a href="#pg097">97</a>, + <a href="#pg100">100</a> +</p> +<p class="ind">static, + <a href="#pg029">29</a> +</p> +<p class="ind">sudden, + <a href="#pg029">29</a> +</p> +<p class="ind">third-point, + <a href="#pg097">97</a> +</p> +<p class="ind">vibratory, + <a href="#pg029">29</a> +</p> + +<p>Locust, + <a href="#pg022">22</a> +</p> +<p class="ind">black, + <a href="#pg013">13</a>, + <a href="#pg040">40</a>, + <a href="#pg044">44</a>, + <a href="#pg051">51</a> +</p> +<p class="ind">honey, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg056">56</a> +</p> + +<p>Log of tests, + <a href="#pg097">97</a>-98, + <a href="#pg100">100</a>-102, + <a href="#pg103">103</a>-104, + <a href="#pg107">107</a>, + <a href="#pg110">110</a>, + <a href="#pg114">114</a> +</p> + +<p>Machine for static tests, + <a href="#pg090">90</a>-92 +Maple, + <a href="#pg022">22</a>, + <a href="#pg044">44</a>, + <a href="#pg051">51</a> +</p> +<p class="ind">red, + <a href="#pg013">13</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg056">56</a> +</p> +<p class="ind">silver, + <a href="#pg013">13</a> +</p> +<p class="ind">sugar, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg056">56</a> +</p> + +<p>Marking test specimens, + <a href="#pg094">94</a>-95, + <a href="#pg100">100</a>, + <a href="#pg129">129</a>-131 +</p> + +<p>Material for tests, + <a href="#pg088">88</a>-90, + <a href="#pg094">94</a>, + <a href="#pg099">99</a>-100, + <a href="#pg102">102</a>, + <a href="#pg106">106</a>, + <a href="#pg107">107</a>-110, + <a href="#pg113">113</a>, + <a href="#pg115">115</a>-116, + <a href="#pg117">117</a>, + <a href="#pg118">118</a>, + <a href="#pg119">119</a>-120, + <a href="#pg121">121</a>, + <a href="#pg122">122</a>, + <a href="#pg123">123</a>-125, + <a href="#pg128">128</a>-134, + <a href="#pg135">135</a>, + <a href="#pg136">136</a> +</p> + +<p>Mechanical properties, definition of, + <a href="#pg001">1</a> +</p> +<p class="ind">factors affecting, + <a href="#pg043">43</a>-87 +</p> + +<p>Medullary rays (<a href="#Rays">see Rays</a>) +</p> + +<p>Mistletoe, + <a href="#pg070">70</a> +</p> + +<a name="Modulus_of_elasticity"></a> +<p>Modulus of elasticity, + <a href="#pg006">6</a>, + <a href="#pg025">25</a>, + <a href="#pg089">89</a> +</p> +<p class="ind2">formulæ, + <a href="#pg098">98</a>, + <a href="#pg102">102</a>, + <a href="#pg104">104</a>, + <a href="#pg114">114</a>, + <a href="#pg123">123</a> +</p> +<p class="ind">of rupture, + <a href="#pg026">26</a>, + <a href="#pg054">54</a>, + <a href="#pg062">62</a>, + <a href="#pg075">75</a> +</p> +<p class="ind2">formulæ, + <a href="#pg098">98</a>, + <a href="#pg102">102</a> +</p> +<p class="ind">speed-strength, + <a href="#pg094">94</a> +</p> + +<p>Moisture, determination, + <a href="#pg090">90</a>, + <a href="#pg133">133</a>-134 +</p> +<p class="ind">effect of, + <a href="#pg006">6</a>, + <a href="#pg008">8</a>, + <a href="#pg017">17</a>, + <a href="#pg033">33</a>, + <a href="#pg075">75</a>-84, + <a href="#pg138">138</a>-139 +</p> + +<p>Mulberry, + <a href="#pg044">44</a>, + <a href="#pg051">51</a> +</p> + +<p>Natural shape and size, + <a href="#pg002">2</a> +</p> + +<p>Neutral axis, + <a href="#pg023">23</a> +</p> +<p class="ind">plane, + <a href="#pg023">23</a>, + <a href="#pg033">33</a> +</p> + +<p>Oak, + <a href="#pg015">15</a>, + <a href="#pg022">22</a>, + <a href="#pg043">43</a>, + <a href="#pg048">48</a>, + <a href="#pg049">49</a>, + <a href="#pg055">55</a>, + <a href="#pg060">60</a>, + <a href="#pg066">66</a>, + <a href="#pg071">71</a>, + <a href="#pg084">84</a> +</p> +<p class="ind">black, + <a href="#pg040">40</a> +</p> +<p class="ind">bur, + <a href="#pg013">13</a> +</p> +<p class="ind">live, + <a href="#pg022">22</a> +</p> +<p class="ind">post, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg056">56</a> +</p> +<p class="ind">red, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg056">56</a>, + <a href="#pg124">124</a> +</p> +<p class="ind">southern, + <a href="#pg052">52</a>, + <a href="#pg071">71</a> +</p> +<p class="ind">swamp white, + <a href="#pg009">9</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg042">42</a>, + <a href="#pg056">56</a> +</p> +<p class="ind">tanbark, + <a href="#pg056">56</a> +</p> +<p class="ind">white, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg054">54</a>, + <a href="#pg056">56</a>, + <a href="#pg072">72</a>, + <a href="#pg144">144</a> +</p> +<p class="ind">yellow, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg042">42</a>, + <a href="#pg056">56</a> +</p> + +<p>Osage orange, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg051">51</a>, + <a href="#pg056">56</a> +</p> + +<p>Oven-dry, + <a href="#pg057">57</a> +</p> + +<p>Packing Boxes, testing, + <a href="#pg124">124</a> +</p> + +<p>Permanent set, + <a href="#pg005">5</a> +</p> + +<p>Permeability, + <a href="#pg054">54</a> +</p> + +<p>Pitch pockets, + <a href="#pg065">65</a> +</p> + +<p>Pith rays (<a href="#Rays">see Rays</a>) +</p> + +<p>Pine, + <a href="#pg044">44</a>, + <a href="#pg045">45</a>, + <a href="#pg055">55</a> +</p> +<p class="ind">Cuban, + <a href="#pg071">71</a> +</p> +<p class="ind">loblolly, + <a href="#pg036">36</a>, + <a href="#pg048">48</a>, + <a href="#pg051">51</a>, + <a href="#pg054">54</a>, + <a href="#pg071">71</a>, + <a href="#pg085">85</a>, + <a href="#pg140">140</a>, + <a href="#pg141">141</a>, + <a href="#pg142">142</a>, + <a href="#pg143">143</a> +</p> +<p class="ind">lodgepole, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg057">57</a> +</p> +<p class="ind">longleaf, + <a href="#pg006">6</a>, + <a href="#pg007">7</a>, + <a href="#pg008">8</a>, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg014">14</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg036">36</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg046">46</a>, + <a href="#pg057">57</a>, + <a href="#pg059">59</a>, + <a href="#pg065">65</a>, + <a href="#pg071">71</a>, + <a href="#pg078">78</a>, + <a href="#pg140">140</a>, + <a href="#pg141">141</a>, + <a href="#pg142">142</a>, + <a href="#pg143">143</a>, + <a href="#pg144">144</a> +</p> +<p class="ind">northern yellow, + <a href="#pg022">22</a> +</p> +<p class="ind">Norway (<a href="#Red_pine">see Red pine</a>) +</p> +<a name="Red_pine"></a> +<p class="ind">red, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg036">36</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg048">48</a>, + <a href="#pg057">57</a>, + <a href="#pg140">140</a>, + <a href="#pg141">141</a>, + <a href="#pg142">142</a>, + <a href="#pg143">143</a>, + <a href="#pg144">144</a> +</p> +<p class="ind">shortleaf, + <a href="#pg013">13</a>, + <a href="#pg027">27</a>, + <a href="#pg036">36</a>, + <a href="#pg048">48</a>, + <a href="#pg057">57</a>, + <a href="#pg071">71</a>, + <a href="#pg140">140</a>, + <a href="#pg141">141</a>, + <a href="#pg142">142</a>, + <a href="#pg143">143</a>, + <a href="#pg144">144</a> +</p> +<p class="ind">southern yellow, + <a href="#pg022">22</a>, + <a href="#pg124">124</a> +</p> +<p class="ind">sugar, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg042">42</a>, + <a href="#pg057">57</a> +</p> +<p class="ind">western yellow, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg057">57</a> +</p> +<p class="ind">white, + <a href="#pg013">13</a>, + <a href="#pg015">15</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg022">22</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg051">51</a>, + <a href="#pg057">57</a>, + <a href="#pg144">144</a> +</p> + +<p>Plane, neutral, + <a href="#pg023">23</a>, + <a href="#pg033">33</a> +</p> + +<p>Plasticity, + <a href="#pg006">6</a> +</p> + +<p>Pliability, + <a href="#pg005">5</a>, + <a href="#pg038">38</a>, + <a href="#pg085">85</a> +</p> + +<p>Poplar, + <a href="#pg022">22</a>, + <a href="#pg044">44</a> +</p> +<p class="ind">yellow, + <a href="#pg044">44</a> +</p> + +<p>Pores, + <a href="#pg044">44</a> +</p> + +<p>Preservatives, effect of, + <a href="#pg086">86</a> +</p> + +<a name="Rays"></a> +<p>Rays, + <a href="#pg060">60</a> +</p> +<p class="ind">effect on compression failure, + <a href="#pg017">17</a>, + <a href="#pg018">18</a> +</p> +<p class="ind">shrinkage, + <a href="#pg081">81</a>-82 +</p> + +<p>Redwood, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg027">27</a>, + <a href="#pg036">36</a>, + <a href="#pg048">48</a>, + <a href="#pg057">57</a>, + <a href="#pg140">140</a>, + <a href="#pg141">141</a>, + <a href="#pg142">142</a>, + <a href="#pg143">143</a>, + <a href="#pg144">144</a> +</p> + +<a name="Resilience"></a> +<p>Resilience, + <a href="#pg002">2</a>, + <a href="#pg005">5</a>, + <a href="#pg049">49</a> +</p> +<p class="ind">elastic, + <a href="#pg006">6</a> +</p> +<p class="ind2">formulæ for, + <a href="#pg098">98</a>, + <a href="#pg102">102</a>, + <a href="#pg104">104</a>, + <a href="#pg114">114</a> +</p> + +<p>Resin, effect of, + <a href="#pg059">59</a> +</p> +<p class="ind">pockets, + <a href="#pg065">65</a> +</p> + +<p>Rind-gall, + <a href="#pg065">65</a> +</p> + +<p>Ring, annual, + <a href="#pg044">44</a> +</p> +<p class="ind">growth, + <a href="#pg044">44</a>, + <a href="#pg052">52</a> +</p> +<p class="ind">-shake, + <a href="#pg064">64</a>-65 +</p> +<p class="ind">-porous, + <a href="#pg044">44</a>, + <a href="#pg059">59</a> +</p> + +<p>Rot, + <a href="#pg068">68</a>, + <a href="#pg069">69</a> +</p> + +<p>Rupture, modulus of, + <a href="#pg026">26</a>, + <a href="#pg054">54</a>, + <a href="#pg062">62</a>, + <a href="#pg075">75</a> +</p> +<p class="ind">formulæ, + <a href="#pg098">98</a>, + <a href="#pg102">102</a> +</p> + +<p>Safe Load, + <a href="#pg029">29</a> +</p> + +<p>Sap, + <a href="#pg073">73</a>, + <a href="#pg074">74</a> +</p> +<p class="ind">-stain, + <a href="#pg059">59</a> +</p> +<p class="ind">-wood, + <a href="#pg050">50</a>-54, + <a href="#pg073">73</a>, + <a href="#pg074">74</a> +</p> + +<p>Sassafras, + <a href="#pg051">51</a> +</p> + +<p>Season checks, + <a href="#pg061">61</a>, + <a href="#pg078">78</a>-84 +</p> +<p class="ind">of cutting, effect of, + <a href="#pg073">73</a>-75 +</p> + +<p>Seasoning, + <a href="#pg055">55</a>, + <a href="#pg074">74</a>, + <a href="#pg075">75</a>-84 +</p> + +<p>Second-growth, + <a href="#pg049">49</a>, + <a href="#pg050">50</a> +</p> + +<p>Set, + <a href="#pg005">5</a> +</p> + +<p>Shake, + <a href="#pg064">64</a>-66, + <a href="#pg072">72</a> +</p> +<p class="ind">cup, + <a href="#pg064">64</a> +</p> +<p class="ind">heart, + <a href="#pg064">64</a> +</p> +<p class="ind">ring, + <a href="#pg064">64</a> +</p> +<p class="ind">star, + <a href="#pg064">64</a> +</p> + +<p>Shear 3, + <a href="#pg019">19</a>-22, + <a href="#pg133">133</a> +</p> +<p class="ind">across the grain, + <a href="#pg019">19</a>, + <a href="#pg021">21</a>, + <a href="#pg022">22</a> +</p> +<p class="ind">along the grain, + <a href="#pg019">19</a>, + <a href="#pg021">21</a>, + <a href="#pg076">76</a>, + <a href="#pg094">94</a>, + <a href="#pg107">107</a>-110 +</p> +<p class="ind2">formulæ, + <a href="#pg098">98</a>, + <a href="#pg102">102</a> +</p> +<p class="ind">horizontal, + <a href="#pg024">24</a> +</p> +<p class="ind">failure, + <a href="#pg035">35</a>-37 +</p> +<p class="ind">longitudinal, + <a href="#pg021">21</a>, + <a href="#pg024">24</a> +</p> +<p class="ind">oblique, + <a href="#pg021">21</a>, + <a href="#pg022">22</a> +</p> +<p class="ind">transverse, + <a href="#pg023">23</a> +</p> +<p class="ind">vertical, + <a href="#pg023">23</a> +</p> + +<p>Shearing strength, + <a href="#pg002">2</a>, + <a href="#pg019">19</a> +</p> + +<p>Shipping dry, + <a href="#pg057">57</a> +</p> + +<p>Shipworms, + <a href="#pg067">67</a> +</p> + +<p>Shock, + <a href="#pg030">30</a>, + <a href="#pg049">49</a> +</p> + +<p>Shortening, + <a href="#pg003">3</a>, + <a href="#pg033">33</a> +</p> + +<p>Shrinkage, + <a href="#pg054">54</a>, + <a href="#pg058">58</a>, + <a href="#pg074">74</a>, + <a href="#pg076">76</a>, + <a href="#pg078">78</a>-82, + <a href="#pg135">135</a>-137 +</p> + +<p><i>S</i>-irons, + <a href="#pg083">83</a> +</p> + +<p>Site, effect on wood, + <a href="#pg048">48</a>, + <a href="#pg049">49</a>, + <a href="#pg070">70</a>-73 +</p> + +<p>Size of test specimens, effect of, + <a href="#pg089">89</a>-90, + <a href="#pg138">138</a>-139 +</p> + +<p>Sketching test specimens, + <a href="#pg094">94</a>-95, + <a href="#pg100">100</a>, + <a href="#pg102">102</a>, + <a href="#pg106">106</a> +</p> + +<p>Softwood, + <a href="#pg044">44</a>, + <a href="#pg060">60</a> +</p> + +<p>Span, + <a href="#pg025">25</a> +</p> + +<p>Specific gravity, + <a href="#pg055">55</a>, + <a href="#pg135">135</a>-137 +</p> + +<p>Speed of testing machine, + <a href="#pg093">93</a>-94 +</p> +<p class="ind">-strength modulus, + <a href="#pg094">94</a> +</p> + +<p><i>Sphæeroma</i>, + <a href="#pg067">67</a> +</p> + +<p>Spike-pulling test, + <a href="#pg123">123</a> +</p> + +<p>Spiral grain, + <a href="#pg060">60</a> +</p> + +<p>Splintering tension failure, + <a href="#pg034">34</a> +</p> + +<p>Splitting, + <a href="#pg041">41</a>, + <a href="#pg060">60</a> +</p> + +<p>Spring wood (<a href="#Early_wood">see Early wood</a>) +</p> + +<p>Spruce, + <a href="#pg014">14</a>, + <a href="#pg015">15</a>, + <a href="#pg022">22</a>, + <a href="#pg044">44</a>, + <a href="#pg059">59</a>, + <a href="#pg075">75</a>, + <a href="#pg084">84</a>, + <a href="#pg144">144</a> +</p><p class="ind">Engelmann, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg057">57</a> +</p> +<p class="ind">red, + <a href="#pg007">7</a>, + <a href="#pg013">13</a>, + <a href="#pg027">27</a>, + <a href="#pg057">57</a>, + <a href="#pg140">140</a>, + <a href="#pg141">141</a> +</p> +<p class="ind">white, + <a href="#pg013">13</a>, + <a href="#pg027">27</a>, + <a href="#pg057">57</a>, + <a href="#pg140">140</a>, + <a href="#pg141">140</a> +</p> + +<p>Static tests, machine for, + <a href="#pg090">90</a>-92 +</p> + +<p>Steaming, effect of, + <a href="#pg085">85</a>, + <a href="#pg087">87</a> +</p> + +<p>Stiffness, + <a href="#pg001">1</a>, + <a href="#pg004">4</a>, + <a href="#pg005">5</a>, + <a href="#pg006">6</a>, + <a href="#pg025">25</a>, + <a href="#pg026">26</a>, + <a href="#pg062">62</a>, + <a href="#pg076">76</a> +</p> + +<p>Strain, definition of, + <a href="#pg002">2</a> +</p> +<p class="ind">unit, + <a href="#pg003">3</a> +</p> + +<p>Stress, compressive, + <a href="#pg003">3</a> +</p> +<p class="ind">definition of, + <a href="#pg002">2</a> +</p> +<p class="ind">due to impact, + <a href="#pg031">31</a>, + <a href="#pg032">32</a> +</p> +<p class="ind">external, + <a href="#pg002">2</a>, + <a href="#pg033">33</a> +</p> +<p class="ind">internal, + <a href="#pg002">2</a> +</p> +<p class="ind">shearing, + <a href="#pg003">3</a>, + <a href="#pg021">21</a> +</p> +<p class="ind">tensile, + <a href="#pg003">3</a>, + <a href="#pg062">62</a> +</p> +<p class="ind">torsional, + <a href="#pg038">38</a> +</p> + +<p>Stress, unit, + <a href="#pg003">3</a> +</p> +<p class="ind">-strain diagram, + <a href="#pg003">3</a>, + <a href="#pg097">97</a>-98, + <a href="#pg100">100</a> +</p> + +<p>Structural timbers, strength of, + <a href="#pg138">138</a>-144 +</p> + +<p>Summer wood, (<a href="#Late_wood">see Late wood</a>) +</p> + +<p>Sycamore, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg042">42</a>, + <a href="#pg057">57</a>, + <a href="#pg064">64</a> +</p> + +<p>Tamarack, + <a href="#pg009">9</a>, + <a href="#pg013">13</a>, + <a href="#pg016">16</a>, + <a href="#pg020">20</a>, + <a href="#pg027">27</a>, + <a href="#pg032">32</a>, + <a href="#pg036">36</a>, + <a href="#pg040">40</a>, + <a href="#pg042">42</a>, + <a href="#pg048">48</a>, + <a href="#pg057">57</a>, + <a href="#pg140">140</a>, + <a href="#pg141">141</a>, + <a href="#pg142">142</a>, + <a href="#pg143">143</a>, + <a href="#pg144">144</a> +</p> + +<p>Temperature, effect of, + <a href="#pg084">84</a>-86 +</p> + +<p>Tensile strength, + <a href="#pg001">1</a>, + <a href="#pg007">7</a>, + <a href="#pg023">23</a>, + <a href="#pg078">78</a> +</p> +<p class="ind">parallel to grain, + <a href="#pg007">7</a>, + <a href="#pg008">8</a> +</p> +<p class="ind">right angles to grain, + <a href="#pg008">8</a> +</p> + +<p>Tension, + <a href="#pg007">7</a> +</p> +<p class="ind">failures, + <a href="#pg034">34</a> +</p> +<p class="ind">tests, + <a href="#pg118">118</a>-122 +</p> + +<p>Teredo, + <a href="#pg067">67</a> +</p> + +<p>Tests, impact, + <a href="#pg031">31</a>-33 +</p> +<p class="ind">timber, + <a href="#pg088">88</a>-136 +</p> + +<p>Test specimens, size of, + <a href="#pg089">89</a>-90 +</p> + +<p>Timber testing, + <a href="#pg088">88</a>-136 +</p> + +<p>Vehicle woods, testing, + <a href="#pg124">124</a> +</p> + +<p>Variability of wood, + <a href="#pg001">1</a>, + <a href="#pg002">2</a>, + <a href="#pg043">43</a> +</p> + +<p>Walnut, black, + <a href="#pg022">22</a> +</p> +<p class="ind">common, + <a href="#pg022">22</a> +</p> + +<p>Water content, + <a href="#pg055">55</a>, + <a href="#pg073">73</a>, + <a href="#pg074">74</a> +</p> +<p class="ind">effect of, + <a href="#pg006">06</a>, + <a href="#pg008">08</a>, + <a href="#pg017">17</a>, + <a href="#pg033">33</a>, + <a href="#pg075">75</a>-84 +</p> + +<p>Wear, resistance to (<a href="#Abrasion">see Abrasion</a>) +</p> + +<p>Weight, relation to mechanical properties, + <a href="#pg054">54</a>-55 +</p> + +<p>Willow, + <a href="#pg044">44</a> +</p> +<p class="ind">black, + <a href="#pg013">13</a> +</p> + +<p>Work (<a href="#Resilience">see Resilience</a>), + <a href="#pg030">30</a>, + <a href="#pg054">54</a> +</p> + +<p>Working plan, + <a href="#pg088">88</a>, + <a href="#pg127">127</a>-137 +</p> + +<p>Xylotrya, + <a href="#pg067">67</a> +</p> + +<p>Yellow Poplar, + <a href="#pg044">44</a> +</p> + +<p>Zinc Chloride, effect of, + <a href="#pg087">87</a> +</p> + +<a name="FOOTNOTES"></a><h2>FOOTNOTES</h2> + +<a name="fn01"></a><a href="#fn01r">return</a> +<p>[Footnote 1: This is in accordance with the discovery made in +1678 by Robert Hooke, and is known as <i>Hooke's law</i>.]</p> + +<a name="fn02"></a><a href="#fn02r">return</a> +<p>[Footnote 2: If the straight portion does not pass through the +origin, a parallel line should be drawn through the origin, and +the load at elastic limit taken from this line. (<a href="#fig32">See Fig. 32</a>.)]</p> + +<a name="fn03"></a><a href="#fn03r">return</a> +<p>[Footnote 3: See Brush, Warren D.: A microscopic study of the +mechanical failure of wood. Vol. II, Rev. F.S. Investigations, +Washington, D.C., 1912, p. 35.]</p> + +<a name="fn04"></a><a href="#fn04r">return</a> +<p>[Footnote 4: See Circular No. 18, U.S. Division of Forestry: +Progress in timber physics, pp. 13-18; also Bulletin 70, U.S. +Forest Service: Effect of moisture on the strength and stiffness +of wood, pp. 42, 89-90.]</p> + +<a name="fn05"></a><a href="#fn05r">return</a> +<p>[Footnote 5: See Bulletin 70, <i>op. cit.</i>, p. 129.]</p> + +<a name="fn06"></a><a href="#fn06r">return</a> +<p>[Footnote 6: Jaccard, P.: Étude anatomique des bois comprimés. +Mit. d. Schw. Centralanstalt f.d. forst. Versuchswesen. X. Band, +1. Heft. Zurich, 1910, p. 66.]</p> + +<a name="fn07"></a><a href="#fn07r">return</a> +<p>[Footnote 7: This does not correspond exactly with the +conclusions of A. Thil, who says ("Constitution anatomique du +bois," pp. 140-141): "The sides of the medullary rays sometimes +produce planes of least resistance varying in size with the +height of the rays. The medullary rays assume a direction more +or less parallel to the lumen of the cells on which they border; +the latter curve to the right or left to make room for the ray +and then close again beyond it. If the force acts parallel to +the axis of growth, the tracheids are more likely to be +displaced if the marginal cells of the medullary rays are +provided with weak walls that are readily compressed. This +explains why on the radial surface of the test blocks the plane +of rupture passes in a direction nearly following a medullary +ray, whereas on the tangential surface the direction of the +plane of rupture is oblique—but with an obliquity varying with +the species and determined by the pitch of the spirals along +which the medullary rays are distributed in the stem." See +Jaccard, <i>op. cit.</i>, pp. 57 <i>et seq.</i>]</p> + +<a name="fn08"></a><a href="#fn08r">return</a> +<p>[Footnote 8: Shear should not be confused with ordinary cutting +or incision.]</p> + +<a name="fn09"></a><a href="#fn09r">return</a> +<p>[Footnote 9: While in reality this relationship does not exactly +hold, the formulæ for beams are based on its assumption.]</p> + +<a name="fn10"></a><a href="#fn10r">return</a> +<p>[Footnote 10: Only this form of beam is considered since it is +the simplest. For cantilever and continuous beams, and beams +rigidly fixed at one or both ends, as well as for different +methods of loading, different forms of cross section, etc., +other formulæ are required. See any book on mechanics.]</p> + +<a name="fn11"></a><a href="#fn11r">return</a> +<p>[Footnote 11: See Tiemann, Harry D.: Some results of dead load +bending tests of timber by means of a recording deflectometer. +Proc. Am. Soc. for Testing Materials. Phila. Vol. IX, 1909, pp. +534-548.]</p> + +<a name="fn12"></a><a href="#fn12r">return</a> +<p>[Footnote 12: A fourth might be added, namely, <b>vibratory</b>, or +<b>harmonic repetition</b>, which is frequently serious in the case +of bridges.]</p> + +<a name="fn13"></a><a href="#fn13r">return</a> +<p>[Footnote 13: Johnson, J.B.: The materials of construction, pp. +81-82.]</p> + +<a name="fn14"></a><a href="#fn14r">return</a> +<p>[Footnote 14: See Tiemann, Harry D.: The theory of impact and +its application to testing materials. Jour. Franklin Inst., +Oct., Nov., 1909, pp. 235-259, 336-364.]</p> + +<a name="fn15"></a><a href="#fn15r">return</a> +<p>[Footnote 15: See Proc. Int. Assn. for Testing Materials, 1912, +XXIII<sub><small>2</small></sub>, pp. 12-13.]</p> + +<a name="fn16"></a><a href="#fn16r">return</a> +<p>[Footnote 16: See articles by Gabriel Janka listed in +bibliography, <a href="#pg151">pages 151-152</a>.]</p> + +<a name="fn17"></a><a href="#fn17r">return</a> +<p>[Footnote 17: For details regarding the structure of wood see +Record, Samuel J.: Identification of the economic woods of the +United States. New York, John Wiley & Sons, 1912.]</p> + +<a name="fn18"></a><a href="#fn18r">return</a> +<p>[Footnote 18: Bul. 88: Properties and uses of Douglas fir, p. +29.]</p> + +<a name="fn19"></a><a href="#fn19r">return</a> +<p>[Footnote 19: Bul. 108, U. S. Forest Service: Tests of +structural timbers, p. 37.]</p> + +<a name="fn20"></a><a href="#fn20r">return</a> +<p>[Footnote 20: Bul. 80: The commercial hickories, pp. 48-50.]</p> + +<a name="fn21"></a><a href="#fn21r">return</a> +<p>[Footnote 21: Bul. 53: Chestnut in southern Maryland, pp. +20-21.]</p> + +<a name="fn22"></a><a href="#fn22r">return</a> +<p>[Footnote 22: Bul. 108: Tests of structural timber, p. 35.]</p> + +<a name="fn23"></a><a href="#fn23r">return</a> +<p>[Footnote 23: Bul. 80: The commercial hickories, p. 50.]</p> + +<a name="fn24"></a><a href="#fn24r">return</a> +<p>[Footnote 24: <i>Loc. cit.</i>]</p> + +<a name="fn25"></a><a href="#fn25r">return</a> +<p>[Footnote 25: Although the factor of heart or sapwood does not +influence the mechanical properties of the wood and there is +usually no difference in structure observable under the +microscope, nevertheless sapwood is generally decidedly +different from heartwood in its physical properties. It dries +better and more easily than heartwood, usually with less +shrinkage and little checking or honeycombing. This is +especially the case with the more refractory woods, such as +white oaks and <i>Eucalyptus globulus</i> and <i>viminalis</i>. It is +usually much more permeable to air, even in green wood, notably +so in loblolly pine and even in white oak. As already stated, it +is much more subject to decay. The sapwood of white oak may be +impregnated with creosote with comparative ease, while the +heartwood is practically impenetrable. These facts indicate a +difference in its chemical nature.—H.D. Tiemann.]</p> + +<a name="fn26"></a><a href="#fn26r">return</a> +<p>[Footnote 26: Bul. 108, U.S. Forest Service, p. 36.]</p> + +<a name="fn27"></a><a href="#fn27r">return</a> +<p>[Footnote 27: The oaks for some unknown reason fall below the +normal strength for weight, whereas the hickories rise above. +Certain other woods also are somewhat exceptional to the normal +relation of strength and density.]</p> + +<a name="fn28"></a><a href="#fn28r">return</a> +<p>[Footnote 28: Bul. 70, U.S. Forest Service, p. 92; also p. 126, +appendix.]</p> + +<a name="fn29"></a><a href="#fn29r">return</a> +<p>[Footnote 29: See Burke, H.E.: Black check in western hemlock. +Cir. No. 61, U.S. Bu. Entomology, 1905.]</p> + +<a name="fn30"></a><a href="#fn30r">return</a> +<p>[Footnote 30: See McAtee, W.L.: Woodpeckers in relation to trees +and wood products. Bul. No. 39, U.S. Biol. Survey, 1911.]</p> + +<a name="fn31"></a><a href="#fn31r">return</a> +<p>[Footnote 31: See Von Schrenck, Hermann: The "bluing" and the +"red rot" of the western yellow pine, with special reference to +the Black Hills forest reserve. Bul. No. 36, U.S. Bu. Plant +Industry, Washington, 1903, pp. 13-14.</p> + +<p>Weiss, Howard, and Barnum, Charles T.: The prevention of +sapstain in lumber. Cir. 192, U.S. Forest Service, Washington, +1911, pp. 16-17.]</p> + +<a name="fn32"></a><a href="#fn32r">return</a> +<p>[Footnote 32: See Standard classification of structural timber. +Yearbook Am. Soc. for Testing Materials, 1913, pp. 300-303. +Contains three plates showing standard defects.]</p> + +<a name="fn33"></a><a href="#fn33r">return</a> +<p>[Footnote 33: Bul. 108, pp. 52 <i>et seq.</i>]</p> + +<a name="fn34"></a><a href="#fn34r">return</a> +<p>[Footnote 34: Bul. 115, U.S. Forest Service: Mechanical +properties of western hemlock, p. 20.]</p> + +<a name="fn35"></a><a href="#fn35r">return</a> +<p>[Footnote 35: Hartig, R.: The diseases of trees (trans. by +Somerville and Ward), London and New York, 1894, pp. 282-294.]</p> + +<a name="fn36"></a><a href="#fn36r">return</a> +<p>[Footnote 36: Busse, W.: Frost-, Ring- und Kernrisse. Forstwiss. +Centralb., XXXII, 2, 1910, pp. 74-81.]</p> + +<a name="fn37"></a><a href="#fn37r">return</a> +<p>[Footnote 37: For detailed information regarding insect +injuries, the reader is referred to the various publications of +the U.S. Bureau of Entomology, Washington, D.C.]</p> + +<a name="fn38"></a><a href="#fn38r">return</a> +<p>[Footnote 38: See Smith, C. Stowell: Preservation of piling +against marine wood borers. Cir. 128, U.S. Forest Service, 1908, +pp. 15.]</p> + +<a name="fn39"></a><a href="#fn39r">return</a> +<p>[Footnote 39: See Von Schrenck, H.: The decay of timber and +methods of preventing it. Bul. 14, U.S. Bu. Plant Industry, +Washington, D.C., 1902. Also Buls. 32, 114, 214, 266.</p> + +<p>Meineoke, E.P.: Forest tree diseases common in California and +Nevada, U.S. Forest Service, Washington, D.C., 1914.</p> + +<p>Hartig, R.: The diseases of trees. London and New York, 1894.]</p> + +<a name="fn40"></a><a href="#fn40r">return</a> +<p>[Footnote 40: Dry rot in factory timbers, by Inspection Dept. +Associated Factory Mutual Fire Insurance Cos., 31 Milk Street, +Boston, 1913.]</p> + +<a name="fn41"></a><a href="#fn41r">return</a> +<p>[Footnote 41: Falck, Richard: Die Meruliusfaüle des Bauholzes, +Hausschwammforschungen, 6. Heft., Jena, 1912.]</p> + +<a name="fn42"></a><a href="#fn42r">return</a> +<p>[Footnote 42: Mez, Carl: Der Hausschwamm. Dresden, 1908, p. 63.]</p> + +<a name="fn43"></a><a href="#fn43r">return</a> +<p>[Footnote 43: A culture of fungus placed in a glass jar and the +air pumped out ceases to grow, but will start again as soon as +oxygen is admitted.]</p> + +<a name="fn44"></a><a href="#fn44r">return</a> +<p>[Footnote 44: Experiments in kiln-drying <i>Eucalyptus</i> in +Berkeley, U.S. Forest Service.]</p> + +<a name="fn45"></a><a href="#fn45r">return</a> +<p>[Footnote 45: See Anderson, Paul J.: The morphology and life +history of the chestnut blight fungus. Bul. No. 7, Penna. +Chestnut Tree Blight Com., Harrisburg, 1914, p. 17.]</p> + +<a name="fn46"></a><a href="#fn46r">return</a> +<p>[Footnote 46: See York, Harlan H.: The anatomy and some of the +biological aspects of the "American mistletoe." Bul. 120, Sci. +Ser. No. 13, Univ. of Texas, Austin, 1909.</p> + +<p>Bray, Wm. L.: The mistletoe pest in the Southwest. Bul. 166, +U.S. Bu. Plant Ind., Washington, 1910.</p> + +<p>Meinecke, E.P.: Forest tree diseases common in California and +Nevada. U.S. Forest Service, Washington, 1914, pp. 54-58.]</p> + +<a name="fn47"></a><a href="#fn47r">return</a> +<p>[Footnote 47: See Record, S.J.: Sap in relation to the +properties of wood. Proc. Am. Wood Preservers' Assn., Baltimore, +Md., 1913, pp. 160-166.</p> + +<p>Kempfer, Wm. H.: The air-seasoning of timber. In Bul. 161, Am. +Ry. Eng. Assn., 1913, p. 214.]</p> + +<a name="fn48"></a><a href="#fn48r">return</a> +<p>[Footnote 48: See Tiemann, H.D.: Effect of moisture upon the +strength and stiffness of wood. Bul. 70, U.S. Forest Service, +Washington, D.C., 1906; also Cir. 108, 1907.]</p> + +<a name="fn49"></a><a href="#fn49r">return</a> +<p>[Footnote 49: The wood of <i>Eucalyptus globulus</i> (blue gum) +appears to be an exception to this rule. Tiemann says: "The wood +of blue gum begins to shrink immediately from the green +condition, even at 70 to 90 per cent moisture content, instead +of from 30 or 25 per cent as in other species of hardwoods." +Proc. Soc. Am. For., Washington, Vol. VIII, No. 3, Oct., 1913, +p. 313.]</p> + +<a name="fn50"></a><a href="#fn50r">return</a> +<p>[Footnote 50: See Schlich's Manual of Forestry, Vol. V. (rev. +ed.), p. 75.]</p> + +<a name="fn51"></a><a href="#fn51r">return</a> +<p>[Footnote 51: Cir. 39. Experiments on the strength of treated +timber, p. 18.]</p> + +<a name="fn52"></a><a href="#fn52r">return</a> +<p>[Footnote 52: <i>Ibid.</i>, p. 21. See also Cir. 108, p. 19, table +5.]</p> + +<a name="fn53"></a><a href="#fn53r">return</a> +<p>[Footnote 53: Hatt, W. K.: Experiments on the strength of +treated timber. Cir. 39, U.S. Forest Service, 1906, p. 31.]</p> + +<a name="fn54"></a><a href="#fn54r">return</a> +<p>[Footnote 54: Teesdale, Clyde II.: The absorption of creosote by +the cell walls of wood. Cir. 200, U. S. Forest Service, 1912, p. +7.]</p> + +<a name="fn55"></a><a href="#fn55r">return</a> +<p>[Footnote 55: Tiemann, H.D.: Effect of moisture upon the +strength and stiffness of wood. Bul. 70, U. S. Forest Service, +1907, pp. 122-123, tables 43-44.]</p> + +<a name="fn56"></a><a href="#fn56r">return</a> +<p>[Footnote 56: The methods of timber testing described here are +for the most part those employed by the U. S. Forest Service. +See Cir. 38 (rev. ed.), 1909.]</p> + +<a name="fn57"></a><a href="#fn57r">return</a> +<p>[Footnote 57: Bul. 108, U. S. Forest Service: Tests of +structural timbers, pp. 53-54.]</p> + +<a name="fn58"></a><a href="#fn58r">return</a> +<p>[Footnote 58: See Tiemann, Harry Donald: The effect of the speed +of testing upon the strength and the standardization of tests +for speed. Proc. Am. Soc. for Testing Materials, Vol. VIII, +Philadelphia, 1908.]</p> + +<a name="fn59"></a><a href="#fn59r">return</a> +<p>[Footnote 59: For description of U.S. Forest Service automatic +and autographic impact testing machine, see Proc. Am. Soc. for +Testing Materials, Vol. VIII, 1908, pp. 538-540.]</p> + +<a name="fn60"></a><a href="#fn60r">return</a> +<p>[Footnote 60: See Warren, W.H.: The strength, elasticity, and +other properties of New South Wales hardwood timbers. Dept. +For., N.S.W., Sydney, 1911, pp. 88-95.]</p> + +<a name="fn61"></a><a href="#fn61r">return</a> +<p>[Footnote 61: Bul. No. 8: Timber physics, Part II., 1893, p. 7.]</p> + +<a name="fn62"></a><a href="#fn62r">return</a> +<p>[Footnote 62: Cir. 38: Instructions to engineers of timber +tests, 1906, p. 24.]</p> + +<a name="fn63"></a><a href="#fn63r">return</a> +<p>[Footnote 63: Warren, W.H.: The strength, elasticity, and other +properties of New South Wales hardwood timbers, 1911, pp. +58-62.]</p> + +<a name="fn64"></a><a href="#fn64r">return</a> +<p>[Footnote 64: Wood is so seldom subjected to a pure stress of +this kind that the torsion test is usually omitted.]</p> + + + + + + + +<pre> + + + + + +End of the Project Gutenberg EBook of The Mechanical Properties of Wood +by Samuel J. 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