,,the ,,mechanical ,,properties ,,of ,,wood ,illustration3 ,frontispiece4 ,photo by the author4 ,photomicrograph of a small block of western hemlock4 ,at the top is the cross section showing to the right the late wood of one season's growth1 to the left the early wood of the next season4 ,the other two sections are longitudinal and show the fibrous character of the wood4 ,to the left is the radial section with three rays crossing it4 ,to the right is the tangential section upon which the rays appear as vertical rows of beads4 ,x #ce4 ,,the ,,mechanical ,,properties ,,of ,,wood ,including a ,discussion of the ,factors ,affecting the ,mechanical ,properties1 and ,methods of ,timber ,testing ,,by ,,samuel ,j4 ,,record1 ,m4,a41 ,m4,f4 ,,assistant ,,professor ,,of ,,forest ,,products1 ,,yale ,,university ,,first ,,edition ,,first ,,thousand #aiad ,,by ,,the ,,same ,,author ,identification of the ,economic ,woods of the ,united ,states4 #hvo1 vi #aag pages1 #ae figures4 ,cloth1 #a4be net4 ,,to ,,the ,,staff ,,of ,,the ,,forest ,,products ,,laboratory1 ,,at ,,madison1 ,,wisconsin ,,in ,,appreciation ,,of ,,the ,,many ,,opportunities ,,afforded ,,and ,,courtesies ,,extended ,,the ,,author ,,preface ,this book was written primarily for students of forestry to whom a knowledge of the technical properties of wood is essential4 ,the mechanics involved is reduced to the simplest terms and without reference to higher mathematics1 with which the students rarely are familiar4 ,the intention throughout has been to avoid all unnecessarily technical language and descriptions1 thereby making the subject-matter readily available to every one interested in wood4 ,part ,i is devoted to a discussion of the mechanical properties of wood--the relation of wood material to stresses and strains4 ,much of the subject-matter is merely elementary mechanics of materials in general1 though written with reference to wood in particular4 ,numerous tables are included1 showing the various strength values of many of the more important ,american woods4 ,part ,,ii deals with the factors affecting the mechanical properties of wood4 ,this is a subject of interest to all who are concerned in the rational use of wood1 and to the forester it also1 by retrospection1 suggests ways and means of regulating his forest product through control of the conditions of production4 ,attempt has been made1 in the light of all data at hand1 to answer many moot questions1 such as the effect on the quality of wood of rate of growth1 season of cutting1 heartwood and sapwood1 locality of growth1 weight1 water content1 steaming1 and defects4 ,part ,,iii describes methods of timber testing4 ,they are for the most part those followed by the ,u4,s4 ,forest ,service4 ,in schools equipped with the necessary machinery the instructions will serve to direct the tests2 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 research4 ,the appendix contains a copy of the working plan followed by the ,u4,s4 ,forest ,service in the extensive investigations covering the mechanical properties of the woods grown in the ,united ,states4 ,it contains many valuable suggestions for the independent investigator4 ,in addition four tables of strength values for structural timbers1 both green and air-seasoned1 are included4 ,the relation of the stresses developed in different structural forms to those developed in the small clear specimens is given4 ,in the bibliography attempt was made to list all of the important publications and articles on the mechanical properties of wood1 and timber testing4 ,while admittedly incomplete1 it should prove of assistance to the student who desires a fuller knowledge of the subject than is presented here4 ,the writer is indebted to the ,u4,s4 ,forest ,service for nearly all of his tables and photographs as well as many of the data upon which the book is based1 since only the ,government is able to conduct the extensive investigations essential to a thorough understanding of the subject4 ,more than eighty thousand tests have been made at the ,madison laboratory alone1 and the work is far from completion4 ,the writer also acknowledges his indebtedness to ,mr4 ,emanuel ,fritz1 ,m4,e41 ,m4,f41 for many helpful suggestions in the preparation of ,part ,i2 and especially to ,mr4 ,harry ,donald ,tiemann1 ,m4,e41 ,m4,f41 engineer in charge of ,timber ,physics at the ,government ,forest ,products ,laboratory1 ,madison1 ,wisconsin1 for careful revision of the entire manuscript4 ,,samuel ,j4 ,,record4 ,,yale ,,forest ,,school1 ,july #a1 #aiad4 ,,contents ,,preface ,,part ,i ,,the ,,mechanical ,,properties ,,of ,,wood ,introduction ,fundamental considerations and definitions ,tensile strength ,compressive or crushing strength ,shearing strength ,transverse or bending strength3 ,beams ,toughness3 ,torsion ,hardness ,cleavability ,,part ,,ii ,,factors ,,affecting ,,the ,,mechanical ,,properties ,,of ,,wood ,introduction ,rate of growth ,heartwood and sapwood ,weight1 density1 and specific gravity ,color ,cross grain ,knots ,frost splits ,shakes1 galls1 pitch pockets ,insect injuries ,marine wood-borer injuries ,fungous injuries ,parasitic plant injuries ,locality of growth ,season of cutting ,water content ,temperature ,preservatives ,,part ,,iii ,,timber ,,testing ,working plan ,forms of material tested ,size of test specimens ,moisture determination ,machine for static tests ,speed of testing machine ,bending large beams ,bending small beams ,endwise compression ,compression across the grain ,shear along the grain ,impact test ,hardness test3 ,abrasion and indentation ,cleavage test ,tension test parallel to the grain ,tension test at right angles to the grain ,torsion test ,special tests ,spike pulling test ,packing boxes ,vehicle and implement woods ,cross-arms ,other tests ,,appendix ,sample working plan of ,united ,states ,forest ,service ,strength values for structural timbers ,,bibliography ,part ,i3 ,some general works on mechanics1 materials of construction1 and testing of materials ,part ,,ii3 ,publications and articles on the mechanical properties of wood1 and timber testing ,part ,,iii3 ,publications of the ,united ,states ,government on the mechanical properties of wood1 and timber testing ,,illustrations ,frontispiece ,photomicrograph of a small block of western hemlock #a4 ,stress-strain diagrams of two longleaf pine beams #b4 ,compression across the grain #c4 ,side view of failures in compression across the grain #d4 ,end view of failures in compression across the grain #e4 ,testing a buggy-spoke in endwise compression #f4 ,unequal distribution of stress in a long column due to lateral bending #g4 ,endwise compression of a short column #h4 ,failures of a short column of green spruce #i4 ,failures of short columns of dry chestnut #aj4 ,example of shear along the grain #aa4 ,failures of test specimens in shear along the grain #ab4 ,horizontal shear in a beam #ac4 ,oblique shear in a short column #ad4 ,failure of a short column by oblique shear #ae4 ,diagram of a simple beam #af4 ,three common forms of beams--7#a7 simple1 7#b7 cantilever1 7#c7 continuous #ag4 ,characteristic failures of simple beams #ah4 ,failure of a large beam by horizontal shear #ai4 ,torsion of a shaft #bj4 ,effect of torsion on different grades of hickory #ba4 ,cleavage of highly elastic wood #bb4 ,cross-sections of white ash1 red gum1 and eastern hemlock #bc4 ,cross-section of longleaf pine #bd4 ,relation of the moisture content to the various strength values of spruce #be4 ,cross-section of the wood of western larch showing fissures in the thick-walled cells of the late wood #bf4 ,progress of drying throughout the length of a chestnut beam #bg4 ,excessive season checking #bh4 ,control of season checking by the use of ,s-irons #bi4 ,static bending test on a large beam #cj4 ,two methods of loading a beam #ca4 ,static bending test on a small beam #cb4 ,sample log sheet1 giving full details of a transverse bending test on a small pine beam #cc4 ,endwise compression test #cd4 ,sample log sheet of an endwise compression test on a short pine column #ce4 ,compression across the grain #cf4 ,vertical section of shearing tool #cg4 ,front view of shearing tool #ch4 ,two forms of shear test specimens #ci4 ,making a shearing test #dj4 ,impact testing machine #da4 ,drum record of impact bending test #db4 ,abrasion machine for testing the wearing qualities of woods #dc4 ,design of tool for testing the hardness of woods by indentation #dd4 ,design of tool for cleavage test #de4 ,design of cleavage test specimen #df4 ,designs of tension test specimens used in ,united ,states #dg4 ,design of tension test specimen used in ,new ,south ,wales #dh4 ,design of tool and specimen for testing tension at right angles to the grain #di4 ,making a torsion test on hickory #ej4 ,method of cutting and marking test specimens #ea4 ,diagram of specific gravity apparatus ,,tables ,i4 ,comparative strength of iron1 steel1 and wood ,,ii4 ,ratio of strength of wood in tension and in compression ,,iii4 ,right-angled tensile strength of small clear pieces of #be woods in green condition ,,iv4 ,results of compression tests across the grain on #ea woods in green condition1 and comparison with white oak ,v4 ,relation of fibre stress at elastic limit in bending to the crushing strength of blocks cut therefrom in pounds per square inch ,,vi4 ,results of endwise compression tests on small clear pieces of #dj woods in green condition ,,vii4 ,shearing strength along the grain of small clear pieces of #da woods in green condition ,,viii4 ,shearing strength across the grain of various ,american woods ,,ix4 ,results of static bending tests on small clear beams of #di woods in green condition ,x4 ,results of impact bending tests on small clear beams of #cd woods in green condition ,,xi4 ,manner of first failure of large beams ,,xii4 ,hardness of #cb woods in green condition1 as indicated by the load required to imbed a #j4ddd-;inch steel ball to one-half its diameter ,,xiii4 ,cleavage strength of small clear pieces of #cb woods in green condition ,,xiv4 ,specific gravity1 and shrinkage of #ea ,american woods ,,xv4 ,effect of drying on the mechanical properties of wood1 shown in ratio of increase due to reducing moisture content from the green condition to kiln-dry ,,xvi4 ,effect of steaming on the strength of green loblolly pine ,,xvii4 ,speed-strength moduli1 and relative increase in strength at rates of fibre strain increasing in geometric ratio ,,xviii4 ,results of bending tests on green structural timbers ,,xix4 ,results of compression and shear tests on green structural timbers ,,xx4 ,results of bending tests on air-seasoned structural timbers ,,xxi4 ,results of compression and shear tests on air-seasoned structural timbers ,,xxii4 ,working unit stresses for structural timber expressed in pounds per square inch ,,part ,i ,,the ,,mechanical ,,properties ,,of ,,wood ,,introduction ,the mechanical properties of wood are its fitness and ability to resist applied or external forces4 ,by external force is meant any force outside of a given piece of material which tends to deform it in any manner4 ,it is largely such properties that determine the use of wood for structural and building purposes and innumerable other uses of which furniture1 vehicles1 implements1 and tool handles are a few common examples4 ,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 laboratory4 ,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 eliminated4 ,for comparison of different kinds or sizes a standard method of testing is necessary and the values must be expressed in some defined units4 ,for these reasons laboratory experiments if properly conducted have many advantages over any other method4 ,one object of such investigation is to find unit values for strength and stiffness1 etc4 ,these1 because of the complex structure of wood1 cannot have a constant value which will be exactly repeated in each test1 even though no error be made4 ,the most that can be accomplished is to find average values1 the amount of variation above and below1 and the laws which govern the variation4 ,on account of the great variability in strength of different specimens of wood even from the same stick and appearing to be alike1 it is important to eliminate as far as possible all extraneous factors liable to influence the results of the tests4 ,the mechanical properties of wood considered in this book are3 7#a7 stiffness and elasticity1 7#b7 tensile strength1 7#c7 compressive or crushing strength1 7#d7 shearing strength1 7#e7 transverse or bending strength1 7#f7 toughness1 7#g7 hardness1 7#h7 cleavability1 7#i7 resilience4 ,in connection with these1 associated properties of importance are briefly treated4 ,in making use of figures indicating the strength or other mechanical properties of wood for the purpose of comparing the relative merits of different species1 the fact should be borne in mind that there is a considerable range in variability of each individual material and that small differences1 such as a few hundred pounds in values of #aj1jjj pounds1 cannot be considered as a criterion of the quality of the timber4 ,in testing material of the same kind and grade1 differences of #be per cent between individual specimens may be expected in conifers and #ej per cent or even more in hardwoods4 ,the figures given in the tables should be taken as indications rather than fixed values1 and as applicable to a large number collectively and not to individual pieces4 ,,fundamental ,,considerations ,,and ,,definitions ,study of the mechanical properties of a material is concerned mostly with its behavior in relation to stresses and strains1 and the factors affecting this behavior4 ,a stress is a distributed force and may be defined as the mutual action 7#a7 of one body upon another1 or 7#b7 of one part of a body upon another part4 ,in the first case the stress is external2 in the other internal4 ,the same stress may be internal from one point of view and external from another4 ,an external force is always balanced by the internal stresses when the body is in equilibrium4 ,if no external forces act upon a body its particles assume certain relative positions1 and it has what is called its natural shape and size4 ,if sufficient external force is applied the natural shape and size will be changed4 ,this distortion or deformation of the material is known as the strain4 ,every stress produces a corresponding strain1 and within a certain limit 7see elastic limit1 in ,,fundamental ,,considerations ,,and ,,definitions1 above7 the strain is directly proportional to the stress producing it4#a ,the same intensity of stress1 however1 does not produce the same strain in different materials or in different qualities of the same material4 ,no strain would be produced in a perfectly rigid body1 but such is not known to exist4 ,footnote #a3 ,this is in accordance with the discovery made in #afgh by ,robert ,hooke1 and is known as ,hooke's law4 ,stress is measured in pounds 7or other unit of weight or force74 ,a unit stress is the stress on a unit of the sectional ,p area4 ,unit stress --- ,for instance1 if a load 7,p7 of one ,a hundred pounds is uniformly supported by a vertical post with a cross-sectional area 7,a7 of ten square inches1 the unit compressive stress is ten pounds per square inch4 ,strain is measured in inches 7or other linear unit74 ,a unit strain is the strain per unit of length4 ,thus if a post #aj inches long before compression is #i4i inches long under the compressive stress1 the total strain is #j4a inch1 and the unit l #j4a strain is --- ----- #j4ja inch per inch of length4 ,l #aj ,as the stress increases there is a corresponding increase in the strain4 ,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 absciss4 ,this is known as the stress-strain diagram4 ,within the limit mentioned above the diagram is a straight line4 7,see ,fig4 #a47 ,if the results of similar experiments on different specimens are plotted to the same scales1 the diagrams furnish a ready means for comparison4 ,the greater the resistance a material offers to deformation the steeper or nearer the vertical axis will be the line4 ,illustration3 ,,fig4 #a4--,stress-strain diagrams of two longleaf pine beams4 ,e4,l4 elastic limit4 ,the areas of the triangles #j7;,,el7,a and #j7;,,el7,b represent the elastic resilience of the dry and green beams1 respectively4 ,there are three kinds of internal stresses1 namely1 7#a7 tensile1 7#b7 compressive1 and 7#c7 shearing4 ,when external forces act upon a bar in a direction away from its ends or a direct pull1 the stress is a tensile stress2 when toward the ends or a direct push1 compressive stress4 ,in the first instance the strain is an elongation2 in the second a shortening4 ,whenever the forces tend to cause one portion of the material to slide upon another adjacent to it the action is called a shear4 ,the action is that of an ordinary pair of shears4 ,when riveted plates slide on each other the rivets are sheared off4 ,these three simple stresses may act together1 producing compound stresses1 as in flexure4 ,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 side4 ,there is also a tendency of the various fibres to slide past one another in a longitudinal direction4 ,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 contact1 and that the ends would no longer be even4 ,if these pieces were securely glued together they would no longer slip1 but the tendency to do so would exist just the same4 ,moreover1 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 words1 the stiffness of the bow would be materially increased4 ,stiffness is the property by means of which a body acted upon by external forces tends to retain its natural size and shape1 or resists deformation4 ,thus a material that is difficult to bend or otherwise deform is stiff2 one that is easily bent or otherwise deformed is flexible4 ,flexibility is not the exact counterpart of stiffness1 as it also involves toughness and pliability4 ,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 words1 the body is elastic4 ,no substance known is perfectly elastic1 though many are practically so under small loads4 ,eventually a point will be reached where the recovery of the specimen is incomplete4 ,this point is known as the elastic limit1 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 shape4 ,after this limit has been exceeded1 the size and shape of the specimen after removal of the load will not be the same as before1 and the difference or amount of change is known as the permanent set4 ,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 load4 ,in practice the elastic limit of a material under test is determined from the stress-strain diagram4 ,it is that point in the line where the diagram begins perceptibly to curve4#b 7,see ,fig4 #a47 ,footnote #b3 ,if the straight portion does not pass through the origin1 a parallel line should be drawn through the origin1 and the load at elastic limit taken from this line4 7,see ,fig4 #cb47 ,resilience is the amount of work done upon a body in deforming it4 ,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 stress4 ,this may be graphically represented by a diagram in which the absciss represent the amount of deflection and the ordinates the force acting4 ,the area included between the stress-strain curve and the initial line 7which is zero7 represents the work done4 7,see ,fig4 #a47 ,if the unit of space is in inches and the unit of force is in pounds the result is inch-pounds4 ,if the elastic limit is taken as the apex of the triangle the area of the triangle will represent the elastic resilience of the specimen4 ,this amount of work can be applied repeatedly and is perhaps the best measure of the toughness of the wood as a working quality1 though it is not synonymous with toughness4 ,permanent set is due to the plasticity of the material4 ,a perfectly plastic substance would have no elasticity and the smallest forces would cause a set4 ,lead and moist clay are nearly plastic and wood possesses this property to a greater or less extent4 ,the plasticity of wood is increased by wetting1 heating1 and especially by steaming and boiling4 ,were it not for this property it would be impossible to dry wood without destroying completely its cohesion1 due to the irregularity of shrinkage4 ,a substance that can undergo little change in shape without breaking or rupturing is brittle4 ,chalk and glass are common examples of brittle materials4 ,sometimes the word brash is used to describe this condition in wood4 ,a brittle wood breaks suddenly with a clean instead of a splintery fracture and without warning4 ,such woods are unfitted to resist shock or sudden application of load4 ,the measure of the stiffness of wood is termed the modulus of elasticity 7or coefficient of elasticity74 ,it is the ratio of stress per unit of area to the deformation per unit of unit stress length4 ,e ------------- ,it is a number indicative of unit strain stiffness1 not of strength1 and only applies to conditions within the elastic limit4 ,it is nearly the same whether derived from compression tests or from tension tests4 ,a large modulus indicates a stiff material4 ,thus in green wood tested in static bending it varies from #fdc1jjj pounds per square inch for arborvit to #a1ffb1jjj pounds for longleaf pine1 and #a1gfi1jjj pounds for pignut hickory4 7,see ,table ,,ix47 ,the values derived from tests of small beams of dry material are much greater1 approaching #c1jjj1jjj for some of our woods4 ,these values are small when compared with steel which has a modulus of elasticity of about #cj1jjj1jjj pounds per square inch4 7,see ,table ,i47 ---------------------------------------- -------------------------------------- ,,table ,i ---------------------------------------- -------------------------------------- ,,comparative ,,strength ,,of ,,iron1 ,,steel1 ,,and ,,wood ---------------------------------------- -------------------------------------- ,sp4 ,modulus of ,tensile ,crushing ,modulus ,,material gr41 elasticity strength strength of dry in bending rupture ------------------------------ ---------------------------------------- -- ,lbs4 per ,lbs4 per ,lbs4 per ,lbs4 per sq4 in4 sq4 in4 sq4 in4 sq4 in4 ,cast iron1 cold blast 7,hodgkinson7 #g4a #ag1bgj1jjj #af1gjj #ajf1jjj #ch1ejj ,bessenger steel1 high grade 7,fairbain7 #g4h #bi1bae1jjj #hh1djj #bbe1fjj ,longleaf pine1 #c4e moisture 7,u4,s47 4#fc #b1hjj1jjj #ac1jjj #ba1jjj ,redspruce1 #c4e moisture 7,u4,s47 4#da #a1hjj1jjj #h1hjj #ad1ejj ,pignut hickory1 #c4e moisture 7,u4,s47 4#hf #b1cgj1jjj #aa1acj #bd1jjj ---------------------------------------- -------------------------------------- ,,note4--,great variation may be found in different samples of metals as well as of wood4 ,the examples given represent reasonable values4 ---------------------------------------- -------------------------------------- ,,tensile ,,strength ,tension results when a pulling force is applied to opposite ends of a body4 ,this external pull is communicated to the interior1 so that any portion of the material exerts a pull or tensile force upon the remainder1 the ability to do so depending upon the property of cohesion4 ,the result is an elongation or stretching of the material in the direction of the applied force4 ,the action is the opposite of compression4 ,wood exhibits its greatest strength in tension parallel to the grain1 and it is very uncommon in practice for a specimen to be pulled in two lengthwise4 ,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 longitudinally4 ,this is not the case with metals1 and as a result they are used in almost all places where tensile strength is particularly needed1 even though the remainder of the structure1 such as sills1 beams1 joists1 posts1 and flooring1 may be of wood4 ,thus in a wooden truss bridge the tension members are steel rods4 ,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 arrangement4 ,it is greatest in straight-grained specimens with thick-walled fibres4 ,cross grain of any kind materially reduces the tensile strength of wood1 since the tensile strength at right angles to the grain is only a small fraction of that parallel to the grain4 ---------------------------------------- ---------------------- ,,table ,,ii ---------------------------------------- ---------------------- ,,ratio ,,of ,,strength ,,of ,,wood ,,in ,,tension ,,and ,,in ,,compression 7,bul4 #aj1 ,u4 ,s4 ,div4 of ,forestry1 p4 #dd7 ---------------------------------------- ---------------------- ,ratio3 ,a stick #a square inch in cross section4 ,tensile ,,kind ,,of ,,wood strength ,weight required to-- ,r ----------- ---------------------------- compressive ,pull apart ,crush endwise strength ---------------------------------------- ------------------- ,hickory #c4g #cb1jjj #h1ejj ,elm #c4h #bi1jjj #g1ejj ,larch #b4c #ai1djj #h1fjj ,longleaf ,pine #b4b #ag1cjj #g1djj ---------------------------------------- ---------------------- ,,note4--,moisture condition not given4 ---------------------------------------- ---------------------- ,failure of wood in tension parallel to the grain occurs sometimes in flexure1 especially with dry material4 ,the tension portion of the fracture is nearly the same as though the piece were pulled in two lengthwise4 ,the fibre walls are torn across obliquely and usually in a spiral direction4 ,there is practically no pulling apart of the fibres1 that is1 no separation of the fibres along their walls1 regardless of their thickness4 ,the nature of tension failure is apparently not affected by the moisture condition of the specimen1 at least not so much so as the other strength values4#c ,footnote #c3 ,see ,brush1 ,warren ,d43 ,a microscopic study of the mechanical failure of wood4 ,vol4 ,,ii1 ,rev4 ,f4,s4 ,investigations1 ,washington1 ,d4,c41 #aiab1 p4 #ce4 ,tension at right angles to the grain is closely related to cleavability4 ,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 wall4 ---------------------------------------- ---- ,,table ,,iii ---------------------------------------- ---- ,,tensile ,,strength ,,at ,,right ,,angles ,,to ,,the ,,grain ,,of ,,small ,,clear ,,pieces ,,of #be ,,woods ,,in ,,green ,,condition 7,forest ,service ,cir4 #bac7 ---------------------------------------- ---- ,when ,when ,,common ,,name surface of surface of ,,of ,,species failure is failure is radial tangential ---------------------------------------- -- ,lbs4 per ,lbs4 per sq4 inch sq4 inch ,hardwoods ,ash1 white #fde #fga ,basswood #bbf #cjc ,beech #fcc #ifi ,birch1 yellow #ddf #ebf ,elm1 slippery #gfe #hcb ,hackberry #ffa #ghf ,locust1 honey #a1acc #a1dde ,maple1 sugar #faj #hfd ,oak1 post #gad #ibd red #fci #hgd swamp white #geg #iji white #fbb #gdi yellow #gbh #ibi ,sycamore #edj #gha ,tupelo #dgb #gif ,conifers ,arborvit #bda #bce ,cypress1 bald #bdb #bea ,fir1 white #bac #cjd ,hemlock #bga #cbc ,pine1 longleaf #bdj #bih red #agi #bje sugar #bci #cjd western yellow #bcj #beb white #bbe #bhe ,tamarack #bcf #bgd ---------------------------------------- ---- ,,compressive ,,or ,,crushing ,,strength ,compression across the grain is very closely related to hardness and transverse shear4 ,there are two ways in which wood is subjected to stress of this kind1 namely1 7#a7 with the load acting over the entire area of the specimen1 and 7#b7 with a load concentrated over a portion of the area4 7,see ,fig4 #b47 ,the latter is the condition more commonly met with in practice1 as1 for example1 where a post rests on a horizontal sill1 or a rail rests on a cross-tie4 ,the former condition1 however1 gives the true resistance of the grain to simple crushing4 ,illustration3 ,,fig4 #b4--;,compression across the grain4 ,the first effect of compression across the grain is to compact the fibres1 the load gradually but irregularly increasing as the density of the material is increased4 ,if the specimen lies on a flat surface and the load is applied to only a portion of the upper area1 the bearing plate indents the wood1 crushing the upper fibres without affecting the lower part4 7,see ,fig4 #c47 ,as the load increases the projecting ends sometimes split horizontally4 7,see ,fig4 #d47 ,the irregularities in the load are due to the fact that the fibres collapse a few at a time1 beginning with those with the thinnest walls4 ,the projection of the ends increases the strength of the material directly beneath the compressing weight by introducing a beam action which helps support the load4 ,this influence is exerted for a short distance only4 ,illustration3 ,,fig4 #c4--,side view of failures in compression across the grain1 showing crushing of blocks under bearing plate4 ,specimen at right shows splitting at ends4 ,illustration3 ,,fig4 #d4--;,end view of failures in compression across the grain1 showing splitting of the ends of the test specimens4 ,when wood is used for columns1 props1 posts1 and spokes1 the weight of the load tends to shorten the material endwise4 ,this is endwise compression1 or compression parallel to the grain4 ,in the case of long columns1 that is1 pieces in which the length is very great compared with their diameter1 the failure is by sidewise bending or flexure1 instead of by crushing or splitting4 7,see ,fig4 #e47 ,a familiar instance of this action is afforded by a flexible walking-stick4 ,if downward pressure is exerted with the hand on the upper end of the stick placed vertically on the floor1 it will be noted that a definite amount of force must be applied in each instance before decided flexure takes place4 ,after this point is reached a very slight increase of pressure very largely increases the deflection1 thus obtaining so great a leverage about the middle section as to cause rupture4 ,illustration3 ,,fig4 #e4--,testing a buggy spoke in endwise compression1 illustrating the failure by sidewise bending of a long column fixed only at the lower end4 ,photo by ,u4 ,s4 ,forest ,service ,the lateral bending of a column produces a combination of bending with compressive stress over the section1 the compressive stress being maximum at the section of greatest deflection on the concave side4 ,the convex surface is under tension1 as in an ordinary beam test4 7,see ,fig4 #f47 ,if the same stick is braced in such a way that flexure is prevented1 its supporting strength is increased enormously1 since the compressive stress acts uniformly over the section1 and failure is by crushing or splitting1 as in small blocks4 ,in all columns free to bend in any direction the deflection will be seen in the direction in which the column is least stiff4 ,this sidewise bending can be overcome by making pillars and columns thicker in the middle than at the ends1 and by bracing studding1 props1 and compression members of trusses4 ,the strength of a column also depends to a considerable extent upon whether the ends are free to turn or are fixed4 ,illustration3 ,,fig4 #f4--,unequal distribution of stress in a long column due to lateral bending4 ---------------------------------------- --------------- ,,table ,,iv ---------------------------------------- --------------- ,,results ,,of ,,compression ,,tests ,,across ,,the ,,grain ,,on #ea ,,woods ,,in ,,green ,,condition1 ,,and ,,comparison ,,with ,,white ,,oak 7,u4 ,s4 ,forest ,service7 ---------------------------------------- --------------- ,fibre stress ,fiber stress ,,common ,,name at elastic in per cent ,,of ,,species limit of white oak1 perpendicular or #hec pounds to grain per sq4 in4 ---------------------------------------- ------------- ,lbs4 per sq4 inch ,per cent ,osage orange #b1bfj #bfe4j ,honey locust #a1fhd #aig4e ,black locust #a1dbf #afg4b ,post oak #a1adh #acd4f ,pignut hickory #a1adb #acc4i ,water hickory #a1jhh #abg4e ,shagbark hickory #a1jgj #abe4e ,mockernut hickory #a1jab #aah4f ,big shellbark hickory #iig #aaf4i ,bitternut hickory #ihf #aae4g ,nutmeg hickory #ich #aaj4j ,yellow oak #heg #ajj4e ,white oak #hec #ajj4j ,bur oak #hcf #ih4j ,white ash #hbh #ig4a ,red oak #ggh #ia4b ,sugar maple #gdb #hg4j ,rock elm #fif #ha4f ,beech #fjg #ga4b ,slippery elm #eii #gj4b ,redwood #egh #fg4h ,bald cypress #edh #fd4c ,red maple #eca #fb4c ,hackberry #ebe #fa4f ,incense cedar #eah #fj4h ,hemlock #dig #eh4c ,longleaf pine #dia #eg4f ,tamarack #dhj #ef4c ,silver maple #def #ec4e ,yellow birch #ded #ec4b ,tupelo #dea #eb4i ,black cherry #ddd #eb4a ,sycamore #dcc #ej4h ,douglas fir #dbg #ej4a ,cucumber tree #djh #dg4h ,shortleaf pine #djj #df4i ,red pine #ceh #db4j ,sugar pine #cec #da4a ,white elm #cea #da4b ,western yellow pine #cdh #dj4h ,lodgepole pine #cdh #dj4h ,red spruce #cde #dj4e ,white pine #cad #cf4h ,engelman spruce #bij #cd4j ,arborvit #bhh #cc4h ,largetooth aspen #bfi #ca4e ,white spruce #bfb #cj4g ,butternut #beh #cj4c ,buckeye 7yellow7 #baj #bd4f ,basswood #bji #bd4e ,black willow #aic #bb4f ---------------------------------------- --------------- ,the complexity of the computations depends upon the way in which the stress is applied and the manner in which the stick bends4 ,ordinarily where the length of the test specimen is not greater than four diameters and the ends are squarely faced 7see ,fig4 #g71 the force acts uniformly over each square inch of area and the crushing strength is equal to the maximum load 7,p7 divided ,p by the area of the cross-section 7,a74 ,c --- ,a ,illustration3 ,,fig4 #g4--;,endwise compression of a short column4 ,it has been demonstrated#d that the ultimate strength in compression parallel to the grain is very nearly the same as the extreme fibre stress at the elastic limit in bending4 7,see ,table ,v47 ,in other words1 the transverse strength of beams at elastic limit is practically equal to the compressive strength of the same material in short columns4 ,it is accordingly possible to calculate the approximate breaking strength of beams from the compressive strength of short columns except when the wood is brittle4 ,since tests on endwise compression are simpler1 easier to make1 and less expensive than transverse bending tests1 the importance of this relation is obvious1 though it does not do away with the necessity of making beam tests4 ,footnote #d3 ,see ,circular ,no4 #ah1 ,u4,s4 ,division of ,forestry3 ,progress in timber physics1 pp4 #ac-ah2 also ,bulletin #gj1 ,u4,s4 ,forest ,service3 ,effect of moisture on the strength and stiffness of wood1 pp4 #db1 #hi-ij4 ---------------------------------------- --------------------------------------- ,,table ,v ---------------------------------------- --------------------------------------- ,,relation ,,of ,,fibre ,,stress ,,at ,,elastic ,,limit 7r7 ,,in ,,bending ,,to ,,the ,,crushing ,,strength 7,c7 ,,of ,,blocks ,,cut ,,therefrom1 ,,in ,,pounds ,,per ,,square ,,inch 7,forest ,service ,bul4 #gj1 p4 #ij7 ---------------------------------------- --------------------------------------- ,,longleaf ,,pine ---------------------------------------- --------------------------------------- ,soaked ,green #ad #aa4e #i4e ,kiln-dry ,,moisture ,,condition #ej per #bc per per per per #f4b per cent cent cent cent cent cent ---------------------------------------- -------------------------------- ,number of tests averaged #e #e #e #e #d #e r in bending #d1ibj #e1idd #f1ibd #g1heb #i1bhj #aa1eej ,c in compression #d1ffh #e1ajj #f1dff #g1dff #h1ihe #aj1iaj ,per cent r is in excess of ,c #e4e #af4e #g4a #e4b #c4c #e4i ---------------------------------------- --------------------------------------- ,,spruce ---------------------------------------- --------------------------------------- ,soaked ,green #aj #h4a ,kiln-dry ,,moisture ,,condition #cj per #cj per per per #c4i per cent cent cent cent cent ---------------------------------------- ---------------------------------- ,number of tests averaged #e #d #e #c #d r in bending #c1jjb #c1cfb #f1deh #h1djj #aj1agj ,c in compression #b1fhj #c1jbe #f1abj #g1faj #i1cce ,per cent r is in excess of ,c #ab4j #aa4a #e4e #aj4d #i4j ---------------------------------------- --------------------------------------- ,when a short column is compressed until it breaks1 the manner of failure depends partly upon the anatomical structure and partly upon the degree of humidity of the wood4 ,the fibres 7tracheids in conifers7 act as hollow tubes bound closely together1 and in giving way they either 7#a7 buckle1 or 7#b7 bend4#e ,footnote #e3 ,see ,bulletin #gj1 op4 cit41 p4 #abi4 ,the first is typical of any dry thin-walled cells1 as is usually the case in seasoned white pine and spruce1 and in the early wood of hard pines1 hemlock1 and other species with decided contrast between the two portions of the growth ring4 ,as a rule buckling of a tracheid begins at the bordered pits which form places of least resistance in the walls4 ,in hardwoods such as oak1 chestnut1 ash1 etc41 buckling occurs only in the thinnest-walled elements1 such as the vessels1 and not in the true fibres4 ,according to ,jaccard#f the folding of the cells is accompanied by characteristic alterations of their walls which seem to split them into extremely thin layers4 ,when greatly magnified1 these layers appear in longitudinal sections as delicate threads without any definite arrangements1 while on cross section they appear as numerous concentric strata4 ,this may be explained on the ground that the growth of a fibre is by successive layers which1 under the influence of compression1 are sheared apart4 ,this is particularly the case with thick-walled cells such as are found in late wood4 ,footnote #f3 ,jaccard1 ,p43 tude anatomique des bois comprims4 ,mit4 d4 ,schw4 ,centralanstalt f4d4 forst4 ,versuchswesen4 ,x4 ,band1 #a4 ,heft4 ,zurich1 #aiaj1 p4 #ff4 ---------------------------------------- --------------- ,,table ,,vi ---------------------------------------- --------------- ,,results ,,of ,,endwise ,,compression ,,tests ,,on ,,small ,,clear ,,pieces ,,of #dj ,,woods ,,in ,,green ,,condition 7,forest ,service ,cir4 #bac7 ---------------------------------------- --------------- ,fibre ,modulus ,,common ,,name stress at ,crushing of ,,of ,,species elastic strength elasticity limit ---------------------------------------- ------------ ,lbs4 per ,lbs4 per ,lbs4 per sq4 inch sq4 inch sq4 inch ,hardwoods ,ash1 white #c1eaj #d1bbj #a1eca1jjj ,basswood #ghj #a1hbj #a1jaf1jjj ,beech #b1ggj #c1dhj #a1dab1jjj ,birch1 yellow #b1egj #c1djj #a1iae1jjj ,elm1 slippery #c1daj #c1iij #a1dec1jjj ,hackberry #b1gcj #c1caj #a1jfh1jjj ,hickory1 big shellbark #c1egj #d1ebj #a1feh1jjj bitternut #d1ccj #d1egj #a1faf1jjj mockernut #c1iij #d1cbj #a1cei1jjj nutmeg #c1fbj #c1ihj #a1daa1jjj pignut #c1ebj #d1hbj #a1ihj1jjj shagbark #c1gcj #d1fjj #a1idc1jjj water #c1bdj #d1ffj #a1ibf1jjj ,locust1 honey #d1cjj #d1igj #a1ecf1jjj ,maple1 sugar #c1jdj #c1fgj #a1dfc1jjj ,oak1 post #b1ghj #c1ccj #a1jfb1jjj red #b1bij #c1baj #a1bie1jjj swamp white #c1dgj #d1cfj #a1dhi1jjj white #b1djj #c1ebj #idf1jjj yellow #b1hgj #c1gjj #a1dfe1jjj ,osage orange #c1ihj #e1haj #a1cca1jjj ,sycamore #b1cbj #b1gij #a1jgc1jjj ,tupelo #b1bhj #c1eej #a1bhj1jjj ,conifers ,arborvit #a1dbj #a1iij #ged1jjj ,cedar1 incense #b1gaj #c1jcj #hfh1jjj ,cypress1 bald #c1efj #c1ifj #a1gch1jjj ,fir1 alpine #a1ffj #b1jfj #hhb1jjj amabilis #b1gfc #c1jdj #a1egi1jjj ,douglas #b1cij #b1ibj #a1ddj1jjj white #b1faj #b1hjj #a1ccb1jjj ,hemlock #b1aaj #b1gej #a1jed1jjj ,pine1 lodgepole #b1bij #b1ecj #a1bai1jjj longleaf #c1dbj #d1bhj #a1hij1jjj red #b1dgj #c1jhj #a1fdf1jjj sugar #b1cdj #b1fjj #a1jbi1jjj western yellow #b1ajj #b1dbj #a1bga1jjj white #b1cgj #b1gbj #a1cah1jjj ,redwood #c1dbj #c1hbj #a1age1jjj ,spruce1 ,engelmann #a1hhj #b1agj #a1jba1jjj ,tamarack #c1jaj #c1dhj #a1eif1jjj ---------------------------------------- --------------- ,the second case1 where the fibres bend with more or less regular curves instead of buckling1 is characteristic of any green or wet wood1 and in dry woods where the fibres are thick-walled4 ,in woods in which the fibre walls show all gradations of thickness--in other words1 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 failure1 namely1 buckling and bending1 grade into each other4 ,in woods with very decided contrast between early and late wood the two forms are usually distinct4 ,except in the case of complete failure the cavity of the deformed cells remains open1 and in hardwoods this is true not only of the wood fibres but also of the tube-like vessels4 ,in many cases longitudinal splits occur which isolate bundles of elements by greater or less intervals4 ,the splitting occurs by a tearing of the fibres or rays and not by the separation of the rays from the adjacent elements4 ,illustration3 ,,fig4 #h4--;,failures of short columns of green spruce4 ,illustration3 ,,fig4 #i4--;,failures of short columns of dry chestnut4 ,moisture in wood decreases the stiffness of the fibre walls and enlarges the region of failure4 ,the curve which the fibre walls make in the region of failure is more gradual and also more irregular than in dry wood1 and the fibres are more likely to be separated4 ,in examining the lines of rupture in compression parallel to the grain it appears that there does not exist any specific type1 that is1 one that is characteristic of all woods4 ,test blocks taken from different parts of the same log may show very decided differences in the manner of failure1 while blocks that are much alike in the size1 number1 and distribution of the elements of unequal resistance may behave very similarly4 ,the direction of rupture is1 according to ,jaccard1 not influenced by the distribution of the medullary rays4#g ,these are curved with the bundles of fibres to which they are attached4 ,in any case the failure starts at the weakest points and follows the lines of least resistance4 ,the plane of failure1 as visible on radial surfaces1 is horizontal1 and on the tangential surface it is diagonal4 ,footnote #g3 ,this does not correspond exactly with the conclusions of ,a4 ,thil1 who says 7,constitution anatomique du bois1 pp4 #adj-ada73 ,the sides of the medullary rays sometimes produce planes of least resistance varying in size with the height of the rays4 ,the medullary rays assume a direction more or less parallel to the lumen of the cells on which they border2 the latter curve to the right or left to make room for the ray and then close again beyond it4 ,if the force acts parallel to the axis of growth1 the tracheids are more likely to be displaced if the marginal cells of the medullary rays are provided with weak walls that are readily compressed4 ,this explains why on the radial surface of the test blocks the plane of rupture passes in a direction nearly following a medullary ray1 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 stem4 ,see ,jaccard1 op4 cit41 pp4 #eg et seq4 ,,shearing ,,strength ,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 shear4#h ,in wood this shearing action may be 7#a7 along the grain1 or 7#b7 across the grain4 ,a tenon breaking out its mortise is a familiar example of shear along the grain1 while the shoving off of the tenon itself would be shear across the grain4 ,the use of wood for pins or tree-nails involves resistance to shear across the grain4 ,another common instance of the latter is where the steel edge of the eye of an axe or hammer tends to cut off the handle4 ,in ,fig4 #aj the action of the wooden strut tends to shear off along the grain the portion ,,ab of the wooden tie rod1 and it is essential that the length of this portion be great enough to guard against it4 ,fig4 #aa shows characteristic failures in shear along the grain4 ,footnote #h3 ,shear should not be confused with ordinary cutting or incision4 ,illustration3 ,,fig4 #aj4--;,example of shear along the grain4 ,illustration3 ,,fig4 #aa4--;,failures of test specimens in shear along the grain4 ,in the block at the left the surface of failure is radial2 in the one at the right1 tangential ---------------------------------------- ----- ,,table ,,vii ---------------------------------------- ----- ,,shearing ,,strength ,,along ,,the ,,grain ,,of ,,small ,,clear ,,pieces ,,of #da ,,woods ,,in ,,green ,,condition 7,forest ,service ,cir4 #bac7 ---------------------------------------- ----- ,when ,when ,,common ,,name surface of surface of ,,of ,,species failure is failure is radial tangential ---------------------------------------- --- ,lbs4 per ,lbs4 per sq4 inch sq4 inch ,hardwoods ,ash1 black #hgf #hcb white #a1cfj #a1cab ,basswood #efj #fag ,beech #a1aed #a1cge ,birch1 yellow #a1ajc #a1ahh ,elm1 slippery #a1aig #a1agd white #ggh #hgb ,hackberry #a1jie #a1afa ,hickory1 big shellbark #a1acd #a1aia bitternut #a1acd #a1cdh mockernut #a1bea #a1cac nutmeg #a1jaj #a1jec pignut #a1ccd #a1deg shagbark #a1bcj #a1big water #a1cij #a1dij ,locust1 honey #a1hhe #b1jif ,maple1 red #a1acj #a1ccj sugar #a1aic #a1dee ,oak1 post #a1aif #a1djb red #a1acb #a1aie swamp white #a1aih #a1cid white #a1jif #a1bib yellow #a1afb #a1aif ,sycamore #ijj #a1ajb ,tupelo #igh #a1jhd ,conifers ,arborvit #fag #fad ,cedar1 incense #fac #ffb ,cypress1 bald #hcf #hjj ,fir1 alpine #egc #fed amabilis #eag #fci ,douglas #hec #heh white #gdb #gbc ,hemlock #gij #hac ,pine1 lodgepole #fgb #gdg longleaf #a1jfj #iec red #hab #gda sugar #gjb #gad western yellow #fhf #gjf white #fdi #fci ,spruce1 ,engelmann #fjg #fbd ,tamarack #hhc #hdc ---------------------------------------- ----- ,both shearing stresses may act at the same time4 ,thus the weight carried by a beam tends to shear it off at right angles to the axis2 this stress is equal to the resultant force acting perpendicularly at any point1 and in a beam uniformly loaded and supported at either end is maximum at the points of support and zero at the centre4 ,in addition there is a shearing force tending to move the fibres of the beam past each other in a longitudinal direction4 7,see ,fig4 #ab47 ,this longitudinal shear is maximum at the neutral plane and decreases toward the upper and lower surfaces4 ,illustration3 ,,fig4 #ab4--;,horizontal shear in a beam4 ,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 it4 ,knowledge of shear parallel to the grain is important1 since wood frequently fails in that way4 ,the value of shearing stress parallel to the grain is found by dividing the maximum load in pounds 7,p7 by the area of the cross section in inches 7,a74 ,p ,shear --- ,a ,oblique shearing stresses are developed in a bar when it is subjected to direct tension or compression4 ,the maximum shearing stress occurs along a plane when it makes an angle of #de degrees ,p with the axis of the specimen4 ,in this case1 shear -----4 ,when #b ,a the value of the angle ,greek3 theta is less than #de degrees1 ,p the shear along the plane --- sin ,greek3 theta cos ,greek3 ,a theta4 7,see ,fig4 #ac47 ,the effect of oblique shear is often visible in the failures of short columns4 7,see ,fig4 #ad47 ,illustration3 ,,fig4 #ac4--,oblique shear in a short column4 ,illustration3 ,,fig4 #ad4--;,failure of short column by oblique shear4 ---------------------------------------- ----------------------------------- ,,table ,,viii ---------------------------------------- ----------------------------------- ,,shearing ,,strength ,,across ,,the ,,grain ,,of ,,various ,,american ,,woods 7,j4,c4 ,trautwine4 ,jour4 ,franklin ,institute4 ,vol4 #aji1 #ahhj1 pp4 #aje-ajf7 ---------------------------------------- ----------------------------------- ,,kind ,,of ,,wood ,lbs4 per ,,kind ,,of ,,wood ,lbs4 per sq4 inch sq4 inch ---------------------------------------- -------------------------------- ,ash #f1bhj ,hickory #g1bhe ,beech #e1bbc ,locust #g1agf ,birch #e1eie ,maple #f1cee ,cedar 7white7 #a1cgb ,oak #d1dbe ,cedar 7white7 #a1eai ,oak 7live7 #h1dhj ,cedar 7,central ,amer47 #c1daj ,pine 7white7 #b1dhj ,cherry #b1ide ,pine 7northern yellow7 #d1cdj ,chestnut #a1ecf ,pine 7southernyellow7 #e1gce ,dogwood #f1eaj ,pine 7very resinous yellow7 #e1jec ,ebony #g1gej ,poplar #d1dah ,gum #e1hij ,spruce #c1bee ,hemlock #b1gej ,walnut 7black7 #d1gbh ,hickory #f1jde ,walnut 7common7 #b1hcj ---------------------------------------- ----------------------------------- ,,note4--,two specimens of each were tested4 ,all were fairly seasoned and without defects4 ,the piece sheared off was #e_/h in4 ,the single circular area of each pin was #j4cbb sq4 in4 ---------------------------------------- ----------------------------------- ,,transverse ,,or ,,bending ,,strength3 ,,beams ,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 bend1 they occasion a shortening of the longitudinal fibres on the concave side and an elongation of those on the convex side4 ,within the elastic limit the relative stretching and contraction of the fibres is directly#i proportional to their distances from a plane intermediate between them--the neutral plane4 7,n#a ,p in ,fig4 #ae47 ,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 fibres4 ,similarly for other distances4 ,the elements along the neutral plane experience no tension or compression in an axial direction4 ,the line of intersection of this plane and the plane of section is known as the neutral axis 7,n ,a in ,fig4 #ae7 of the section4 ,footnote #i3 ,while in reality this relationship does not exactly hold1 the formul for beams are based on its assumption4 ,illustration3 ,,fig4 #ae4--;,diagram of a simple beam4 ,n#a ,p neutral plane1 ,n ,a neutral axis of section ,r ,s4 ,if the bar is symmetrical and homogeneous the neutral plane is located half-way between the upper and lower surfaces1 so long as the deflection does not exceed the elastic limit of the material4 ,owing to the fact that the tensile strength of wood is from two to nearly four times the compressive strength1 it follows that at rupture the neutral plane is much nearer the convex than the concave side of the bar or beam1 since the sum of all the compressive stresses on the concave portion must always equal the sum of the tensile stresses on the convex portion4 ,the neutral plane begins to change from its central position as soon as the elastic limit has been passed4 ,its location at any time is very uncertain4 ,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 another4 ,this stress at any point is equal to the resultant perpendicular to the axis of the forces acting at this point1 and is termed the transverse shear 7or in the case of beams1 vertical shear74 ,in addition to this there is a shearing stress1 tending to move the fibres past one another in an axial direction1 which is called longitudinal shear 7or in the case of beams1 horizontal shear74 ,this stress must be taken into consideration in the design of timber structures4 ,it is maximum at the neutral plane and decreases to zero at the outer elements of the section4 ,the shorter the span of a beam in proportion to its height1 the greater is the liability of failure in horizontal shear before the ultimate strength of the beam is reached4 ,beams ,there are three common forms of beams1 as follows3 7#a7 ,simple beam--a bar resting upon two supports1 one near each end4 7,see ,fig4 #af1 ,no4 #a47 7#b7 ,cantilever beam--a bar resting upon one support or fulcrum1 or that portion of any beam projecting out of a wall or beyond a support4 7,see ,fig4 #af1 ,no4 #b47 7#c7 ,continuous beam--a bar resting upon more than two supports4 7,see ,fig4 #af1 ,no4 #c47 ,illustration3 ,,fig4 #af4--,three common forms of beams4 #a4 ,simple4 #b4 ,cantilever4 #c4 ,continuous4 ,stiffness of ,beams ,the two main requirements of a beam are stiffness and strength4 ,the formul for the modulus of elasticity 7,e7 or measure of stiffness of a rectangular prismatic simple beam loaded at the centre and resting freely on supports at either end is3#aj ,footnote #aj3 ,only this form of beam is considered since it is the simplest4 ,for cantilever and continuous beams1 and beams rigidly fixed at one or both ends1 as well as for different methods of loading1 different forms of cross section1 etc41 other formul are required4 ,see any book on mechanics4 ,p' l#c ,e ------------- #d ,d b h#c b breadth or width of beam1 inches4 h height or depth of beam1 inches4 l span 7length between points of supports7 of beam1 inches4 ,d deflection produced by load ,p'1 inches4 ,p' load at or below elastic limit1 pounds4 ,from this formul it is evident that for rectangular beams of the same material1 mode of support1 and loading1 the deflection is affected as follows3 7#a7 ,it is inversely proportional to the width for beams of the same length and depth4 ,if the width is tripled the deflection is one-third as great4 7#b7 ,it is inversely proportional to the cube of the depth for beams of the same length and breadth4 ,if the depth is tripled the deflection is one twenty-seventh as great4 7#c7 ,it is directly proportional to the cube of the span for beams of the same breadth and depth4 ,tripling the span gives twenty-seven times the deflection4 ,the number of pounds which concentrated at the centre will deflect a rectangular prismatic simple beam one inch may be found from the preceding formul by substituting ,d #a and solving for ,p'4 ,the formul then becomes3 #d ,e b h#c ,necessary weight 7,p'7 ------------- l#c ,in this case the values for ,e are read from tables prepared from data obtained by experimentation on the given material4 ,strength of ,beams ,the measure of the breaking strength of a beam is expressed in terms of unit stress by a modulus of rupture1 which is a purely hypothetical expression for points beyond the elastic limit4 ,the formul used in computing this modulus is as follows3 #a4e ,p l ,r --------- b h#b b1 h1 l breadth1 height1 and span1 respectively1 as in preceding formul4 ,r modulus of rupture1 pounds per square inch4 ,p maximum load1 pounds4 ,in calculating the fibre stress at the elastic limit the same formul is used except that the load at elastic limit 7,p#a7 is substituted for the maximum load 7,p74 ,from this formul it is evident that for rectangular prismatic beams of the same material1 mode of support1 and loading1 the load which a given beam can support varies as follows3 7#a7 ,it is directly proportional to the breadth for beams of the same length and depth1 as is the case with stiffness4 7#b7 ,it is directly proportional to the square of the height for beams of the same length and breadth1 instead of as the cube of this dimension as in stiffness4 7#c7 ,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 stiffness4 ,the fact that the strength varies as the square of the height and the stiffness as the cube explains the relationship of bending to thickness4 ,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 piece1 say an inch board4 ---------------------------------------- ---------------------------------------- ----- ,,table ,,ix ---------------------------------------- ---------------------------------------- ----- ,,results ,,of ,,static ,,bending ,,tests ,,on ,,small ,,clear ,,beams ,,of #di ,,woods ,,in ,,green ,,condition 7,forest ,service ,cir4 #bac7 ---------------------------------------- ---------------------------------------- ----- ,fibre ,work in ,bending ,,common ,,name stress at ,modulus ,modulus ------------------------------- ,,of ,,species elastic of of ,to ,to limit rupture elasticity elastic maximum ,total limit load ---------------------------------------- --------------------------------------- ,in4-lbs4 ,in4-lbs4 ,in4-lb4 ,lbs4 per ,lbs4 per ,lbs4 per per cu4 per cu4 per sq4 in4 sq4 in4 sq4 in4 inch inch inch ,hardwoods ,ash1 black #b1ehj #f1jjj #ifj1jjj #j4da #ac4a #ch4i white #e1ahj #i1ibj #a1daf1jjj #a4aj #bj4j #dc4g ,basswood #b1dhj #d1dej #hdb1jjj 4#de #e4h #h4i ,beech #d1dij #h1faj #a1cec1jjj 4#if #ad4a #ca4d ,birch1 yellow #d1aij #h1cij #a1eig1jjj 4#fb #ad4b #ca4e ,elm1 rock #d1bij #i1dcj #a1bbb1jjj 4#ij #ai4d #dg4d slippery #e1efj #i1eaj #a1cad1jjj #a4cb #aa4g #dd4b white #b1hej #f1idj #a1jeb1jjj 4#dd #aa4h #bg4d ,gum1 red #c1dfj #f1dej #a1ach1jjj ,hackberry #c1cbj #g1hjj #a1agj1jjj 4#ef #ai4f #eb4i ,hickory1 big shellbark #f1cgj #aa1aaj #a1efb1jjj #a4dg #bd4c #gh4j bitternut #e1dgj #aj1bhj #a1cii1jjj #a4bb #bj4j #ge4e mockernut #f1eej #aa1aaj #a1ejh1jjj #a4ej #ca4g #hd4d nutmeg #d1hfj #i1jfj #a1bhi1jjj #a4jf #bb4h #eh4b pignut #e1hfj #aa1haj #a1gfi1jjj #a4ab #cj4f #hf4g shagbark #f1abj #aa1jjj #a1geb1jjj #a4bb #ah4c #gb4c water #e1ihj #aj1gdj #a1efc1jjj #a4bi #ah4h #eb4i ,locust1 honey #f1jbj #ab1cfj #a1gcb1jjj #a4bh #ag4c #fd4d ,maple1 red #d1dej #h1caj #a1dde1jjj 4#gh #i4h #ag4a sugar #d1fcj #h1hfj #a1dfb1jjj 4#hh #ab4g #cb4j ,oak1 post #d1gbj #g1chj #iac1jjj #a4ci #i4a #ag4d red #c1dij #g1ghj #a1bfh1jjj 4#fj #aa4d #bf4j swamp white #e1chj #i1hfj #a1eic1jjj #a4je #ad4e #cg4f tanbark #f1ehj #aj1gaj #a1fgh1jjj #a4di white #d1cbj #h1jij #a1acg1jjj 4#ie #ab4a #cf4g yellow #e1jfj #h1egj #a1bai1jjj #a4bj #aa4g #cj4g ,osage orange #g1gfj #ac1ffj #a1cbi1jjj #b4ec #cg4i #aja4g ,sycamore #b1hbj #f1cjj #ifa1jjj 4#ea #g4a #ac4f ,tupelo #d1cjj #g1chj #a1jde1jjj #a4jj #g4h #bj4i ,conifers ,arborvit #b1fjj #d1bej #fdc1jjj 4#fj #e4g #i4e ,cedar1 incense #c1iej #f1jdj #ged1jjj ,cypress1 bald #d1dcj #g1aaj #a1cgh1jjj 4#if #e4a #ae4d ,fir1 alpine #b1cff #d1dej #hfa1jjj 4#ff #d4d #g4d amabilis #d1jfj #f1egj #a1cbc1jjj ,douglas #c1egj #f1cdj #a1bdb1jjj 4#ei #f4f #ac4f white #c1hhj #e1igj #a1aca1jjj 4#gg #e4b #ad4i ,hemlock #c1daj #e1ggj #iag1jjj 4#gc #f4f #ab4i ,pine1 lodgepole #c1jhj #e1acj #a1jae1jjj 4#ed #e4a #g4d longleaf #e1jij #h1fcj #a1ffb1jjj 4#hh #h4a #cd4h red #c1gdj #f1dcj #a1chd1jjj 4#ei #e4h #bh4j shortleaf #d1cfj #g1gaj #a1cie1jjj sugar #c1ccj #e1bgj #iff1jjj 4#ff #e4j #aa4f west1 yellow #c1ahj #e1ahj #a1aaa1jjj 4#eb #d4c #ae4f ,white #c1daj #e1caj #a1jgc1jjj 4#fb #e4i #ac4c ,redwood #d1ecj #f1efj #a1jbd1jjj ,spruce1 ,engelmann #b1gdj #d1eej #hff1jjj 4#ej #d4h #f4a red #c1ddj #e1hbj #a1adc1jjj 4#fb #f4j white #c1afj #e1bjj #ifh1jjj 4#eh #f4f ,tamarack #d1bjj #g1agj #a1bcf1jjj 4#hd #g4b #cj4j ---------------------------------------- ---------------------------------------- ----- ,kinds of ,loads ,there are various ways in which beams are loaded1 of which the following are the most important3 7#a7 ,uniform load occurs where the load is spread evenly over the beam4 7#b7 ,concentrated load occurs where the load is applied at single point or points4 7#c7 ,live or immediate load is one of momentary or short duration at any one point1 such as occurs in crossing a bridge4 7#d7 ,dead or permanent load is one of constant and indeterminate duration1 as books on a shelf4 ,in the case of a bridge the weight of the structure itself is the dead load4 ,all large beams support a uniform dead load consisting of their own weight4 ,the effect of dead load on a wooden beam may be two or more times that produced by an immediate load of the same weight4 ,loads greater than the elastic limit are unsafe and will generally result in rupture if continued long enough4 ,a beam may be considered safe under permanent load when the deflections diminish during equal successive periods of time4 ,a continual increase in deflection indicates an unsafe load which is almost certain to rupture the beam eventually4 ,variations in the humidity of the surrounding air influence the deflection of dry wood under dead load1 and increased deflections during damp weather are cumulative and not recovered by subsequent drying4 ,in the case of longleaf pine1 dry beams may with safety be loaded permanently to within three-fourths of their elastic limit as determined from ordinary static tests4 ,increased moisture content1 due to greater humidity of the air1 lowers the elastic limit of wood so that what was a safe load for the dry material may become unsafe4 ,when a dead load not great enough to rupture a beam has been removed1 the beam tends gradually to recover its former shape1 but the recovery is not always complete4 ,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 stiffness1 ultimate strength1 or elastic limit of the material4 ,in other words1 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 load4#aa ,footnote #aa3 ,see ,tiemann1 ,harry ,d43 ,some results of dead load bending tests of timber by means of a recording deflectometer4 ,proc4 ,am4 ,soc4 for ,testing ,materials4 ,phila4 ,vol4 ,,ix1 #aiji1 pp4 #ecd-edh4 ,maximum load is the greatest load a material will support and is usually greater than the load at rupture4 ,safe load is the load considered safe for a material to support in actual practice4 ,it is always less than the load at elastic limit and is usually taken as a certain proportion of the ultimate or breaking load4 ,the ratio of the breaking to the safe load is called the factor of safety4 7,factor of safety ultimate strength _/ safe load7 ,in order to make due allowance for the natural variations and imperfections in wood and in the aggregate structure1 as well as for variations in the load1 the factor of safety is usually as high as #f or #aj1 especially if the safety of human life depends upon the structure4 ,this means that only from one-sixth to one-tenth of the computed strength values is considered safe to use4 ,if the depth of timbers exceeds four times their thickness there is a great tendency for the material to twist when loaded4 ,it is to overcome this tendency that floor joists are braced at frequent intervals4 ,short deep pieces shear out or split before their strength in bending can fully come into play4 ,application of ,loads ,there are three#ab general methods in which loads may be applied to beams1 namely3 ,footnote #ab3 ,a fourth might be added1 namely1 vibratory1 or harmonic repetition1 which is frequently serious in the case of bridges4 7#a7 ,static loading or the gradual imposition of load so that the moving parts acquire no appreciable momentum4 ,loads are so applied in the ordinary testing machine4 7#b7 ,sudden imposition of load without initial velocity4 ,thus in the case of placing a load on a beam1 if the load be brought into contact with the beam1 but its weight sustained by external means1 as by a cord1 and then this external support be suddenly 7instantaneously7 removed1 as by quickly cutting the cord1 then1 although the load is already touching the beam 7and hence there is no real impact71 yet the beam is at first offering no resistance1 as it has yet suffered no deformation4 ,furthermore1 as the beam deflects the resistance increases1 but does not come to be equal to the load until it has attained its normal deflection4 ,in the meantime there has been an unbalanced force of gravity acting1 of a constantly diminishing amount1 equal at first to the entire load1 at the normal deflection4 ,but at this instant the load and the beam are in motion1 the hitherto unbalanced force having produced an accelerated velocity1 and this velocity of the weight and beam gives to them an energy1 or vis viva1 which must now spend itself in overcoming an excess of resistance over and above the imposed load1 and the whole mass will not stop until the deflection 7as well as the resistance7 has come to be equal to twice that corresponding to the static load imposed4 ,hence we say the effect of a suddenly imposed load is to produce twice the deflection and stress of the same load statically applied4 ,it must be evident1 however1 that this case has nothing in common with either the ordinary 'static' tests of structural materials in testing-machines1 or with impact tests4#ac ,footnote #ac3 ,johnson1 ,j4,b43 ,the materials of construction1 pp4 #ha-hb4 7#c7 ,impact1 shock1 or blow4#ad ,there are various common uses of wood where the material is subjected to sudden shocks and jars or impact4 ,such is the action on the felloes and spokes of a wagon wheel passing over a rough road2 on a hammer handle when a blow is struck2 on a maul when it strikes a wedge4 ,footnote #ad3 ,see ,tiemann1 ,harry ,d43 ,the theory of impact and its application to testing materials4 ,jour4 ,franklin ,inst41 ,oct41 ,nov41 #aiji1 pp4 #bce-bei1 #ccf-cfd4 ,resistance to impact is resistance to energy which is measured by the product of the force into the space through which it moves1 or by the product of one-half the moving mass which causes the shock into the square of its velocity4 ,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 body4 ,it is impossible1 however1 to get all of the energy of the striking body stored in the specimen1 though the greater the mass and the shorter the space through which it moves1 or1 in other words1 the greater the proportion of weight and the smaller the proportion of velocity making up the energy of the striking body1 the more energy the specimen will absorb4 ,the rest is lost in friction1 vibrations1 heat1 and motion of the anvil4 ,in impact the stresses produced become very complex and difficult to measure1 especially if the velocity is high1 or the mass of the beam itself is large compared to that of the weight4 ,the difficulties attending the measurement of the stresses beyond the elastic limit are so great that commonly they are not reckoned4 ,within the elastic limit the formul for calculating the stresses are based on the assumption that the deflection is proportional to the stress in this case as in static tests4 ,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 middle4 7,see ,fig4 #dj47 ,the height of the weight is increased after each drop and records of the deflection taken until failure4 ,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 contact4 ,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 spent3 7a7 ,it produces a local deformation of both bodies at the surface of contact1 within or beyond the elastic limit4 ,in testing wood the compression of the substance of the steel striking-weight may be neglected1 since the steel is very hard in comparison with the wood4 ,in addition to the compression of the fibres at the surface of contact resistance is also offered by the inertia of the particles there1 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 magnitude4 ,it frequently exceeds the crushing strength at the extreme surface of contact1 as in the case of the swaging action of a hammer on the head of an iron spike1 or of a locomotive wheel on the steel rail4 ,this is also the case when a bullet is shot through a board or a pane of glass without breaking it as a whole4 7b7 ,it may move the struck body as a whole with an accelerated velocity1 the resistance consisting of the inertia of the body4 ,this effect is seen when a croquet ball is struck with a mallet4 7c7 ,it may deform a fixed body against its external supports and resistances4 ,in making impact tests in the laboratory the test specimen is in reality in the nature of a cushion between two impacting bodies1 namely1 the striking weight and the base of the machine4 ,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 disregarded4 7d7 ,it may deform the struck body as a whole against the resisting stresses developed by its own inertia1 as1 for example1 when a baseball bat is broken by striking the ball4 ---------------------------------------- --------------- ,,table ,x ---------------------------------------- --------------- ,,results ,,of ,,impact ,,bending ,,tests ,,on ,,small ,,clear ,,beams ,,of #cd ,,woods ,,in ,,green ,,condition 7,forest ,service ,cir4 #bac7 ---------------------------------------- --------------- ,fibre ,work in ,,common ,,name stress at ,modulus of bending ,,of ,,species elastic elasticity to limit elastic limit ---------------------------------------- ------------ ,in4-lbs4 ,lbs4 per ,lbs4 per per cu4 sq4 in4 sq4 in4 inch ,hardwoods ,ash1 black #g1hdj #iee1jjj #c4fi white #aa1gaj #a1efd1jjj #d4ic ,basswood #e1dhj #iag1jjj #a4hd ,beech #aa1gfj #a1eja1jjj #e4aj ,birch1 yellow #aa1jhj #a1hab1jjj #c4gi ,elm1 rock #ab1jij #a1cfg1jjj #f4eb slippery #aa1gjj #a1efi1jjj #d4hf white #i1iaj #a1ach1jjj #d4hb ,hackberry #aj1dbj #a1cih1jjj #d4dh ,locust1 honey #ac1dfj #b1aad1jjj #d4gf ,maple1 red #aa1fgj #a1daa1jjj #e4de sugar #aa1fhj #a1fhj1jjj #d4ee ,oak1 post #aa1bfj #a1eif1jjj #d4da red #aj1ehj #a1ejf1jjj #d4af swamp white #ac1bhj #b1jdh1jjj #d4gi white #i1hfj #a1dad1jjj #c4hd yellow #aj1hdj #a1dgi1jjj #d4dd ,osage orange #ae1ebj #a1dih1jjj #h4ib ,sycamore #h1ahj #a1afe1jjj #c4bb ,tupelo #g1fej #a1caj1jjj #b4di ,conifers ,arborvit #e1bij #ggh1jjj #b4jd ,cypress1 bald #h1bij #a1dca1jjj #b4ga ,fir1 alpine #e1bhj #ihj1jjj #a4ei ,douglas #h1hgj #a1egi1jjj #b4gi white #g1bcj #a1cbf1jjj #b4ba ,hemlock #f1ccj #a1jbe1jjj #b4ai ,pine1 lodgepole #f1hgj #a1adb1jjj #b4ca longleaf #i1fhj #a1gci1jjj #c4jb red #g1dhj #a1dch1jjj #b4ah sugar #f1gdj #a1jhc1jjj #b4cd western yellow #g1jgj #a1aae1jjj #b4ea white #f1dij #a1aef1jjj #b4jf ,spruce1 ,engelmann #f1cjj #a1jgf1jjj #b4ji ,tamarack #g1gej #a1bfc1jjj #b4fg ---------------------------------------- --------------- ,impact testing is difficult to conduct satisfactorily and the data obtained are of chief value in a relative sense1 that is1 for comparing the shock-resisting ability of woods of which like specimens have been subjected to exactly identical treatment4 ,yet this test is one of the most important made on wood1 as it brings out properties not evident from other tests4 ,defects and brittleness are revealed by impact better than by any other kind of test4 ,in common practice nearly all external stresses are of the nature of impact4 ,in fact1 no two moving bodies can come together without impact stress4 ,impact is therefore the commonest form of applied stress1 although the most difficult to measure4 ,failures in ,timber ,beams ,if a beam is loaded too heavily it will break or fail in some characteristic manner4 ,these failures may be classified according to the way in which they develop1 as tension1 compression1 and horizontal shear2 and according to the appearance of the broken surface1 as brash1 and fibrous4 ,a number of forms may develop if the beam is completely ruptured4 ,since the tensile strength of wood is on the average about three times as great as the compressive strength1 a beam should1 therefore1 be expected to fail by the formation in the first place of a fold on the compression side due to the crushing action1 followed by failure on the tension side4 ,this is usually the case in green or moist wood4 ,in dry material the first visible failure is not infrequently on the lower or tension side1 and various attempts have been made to explain why such is the case4#ae ,footnote #ae3 ,see ,proc4 ,int4 ,assn4 for ,testing ,materials1 #aiab1 ,,xxiii#b1 pp4 #ab-ac4 ,within the elastic limit the elongations and shortenings are equal1 and the neutral plane lies in the middle of the beam4 7,see ,,transverse ,,or ,,bending ,,strength3 ,,beams1 above47 ,later the top layer of fibres on the upper or compression side fail1 and on the load increasing1 the next layer of fibres fail1 and so on1 even though this failure may not be visible4 ,as a result the shortenings on the upper side of the beam become considerably greater than the elongations on the lower side4 ,the neutral plane must be presumed to sink gradually toward the tension side1 and when the stresses on the outer fibres at the bottom have become sufficiently great1 the fibres are pulled in two1 the tension area being much smaller than the compression area4 ,the rupture is often irregular1 as in direct tension tests4 ,failure may occur partially in single bundles of fibres some time before the final failure takes place4 ,one reason why the failure of a dry beam is different from one that is moist1 is that drying increases the stiffness of the fibres so that they offer more resistance to crushing1 while it has much less effect upon the tensile strength4 ,there is considerable variation in tension failures depending upon the toughness or the brittleness of the wood1 the arrangement of the grain1 defects1 etc41 making further classification desirable4 ,the four most common forms are3 7#a7,simple tension1 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 grain1 7,see ,fig4 #ag1 ,no4 #a47 ,this is common in straight-grained beams1 particularly when the wood is seasoned4 ,illustration3 ,,fig4 #ag4--;,characteristic failures of simple beams4 7#b7;,cross-grained tension1 in which the fracture is caused by a tensile force acting oblique to the grain4 7,see ,fig4 #ag1 ,no4 #b47 ,this is a common form of failure where the beam has diagonal1 spiral or other form of cross grain on its lower side4 ,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 manner4 7#c7,splintering tension1 in which the failure consists of a considerable number of slight tension failures1 producing a ragged or splintery break on the under surface of the beam4 7,see ,fig4 #ag1 ,no4 #c47 ,this is common in tough woods4 ,in this case the surface of fracture is fibrous4 7#d7;,brittle tension1 in which the beam fails by a clean break extending entirely through it4 7,see ,fig4 #ag1 ,no4 #d47 ,it is characteristic of a brittle wood which gives way suddenly without warning1 like a piece of chalk4 ,in this case the surface of fracture is described as brash4 ,compression failure 7see ,fig4 #ag1 ,no4 #e7 has few variations except that it appears at various distances from the neutral plane of the beam4 ,it is very common in green timbers4 ,the compressive stress parallel to the fibres causes them to buckle or bend as in an endwise compressive test4 ,this action usually begins on the top side shortly after the elastic limit is reached and extends downward1 sometimes almost reaching the neutral plane before complete failure occurs4 ,frequently two or more failures develop at about the same time4 ,horizontal shear failure1 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 7see ,fig4 #ag1 ,no4 #f71 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 large4 ,it is not common in small clear specimens4 ,it is often due to shake or season checks1 common in large timbers1 which reduce the actual area resisting the shearing action considerably below the calculated area used in the formul for horizontal shear4 7,see page #ih for this formul47 ,for this reason it is unsafe1 in designing large timber beams1 to use shearing stresses higher than those calculated for beams that failed in horizontal shear4 ,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 beam4 ,fig4 #ah shows a large beam in which two failures in horizontal shear occurred at the same end4 ,that the parts behave independently is shown by the compression failure below the original location of the neutral plane4 ,illustration3 ,,fig4 #ah4--;,failure of a large beam by horizontal shear4 ,photo by ,u4 ,s1 ,forest ,service4 ,table ,,xi gives an analysis of the causes of first failure in #hdj large timber beams of nine different species of conifers4 ,of the total number tested #afe were air-seasoned1 the remainder green4 ,the failure occurring first signifies the point of greatest weakness in the specimen under the particular conditions of loading employed 7in this case1 third-point static loading74 ---------------------------------------- ------------------- ,,table ,,xi ---------------------------------------- ------------------- ,,manner ,,of ,,first ,,failure ,,of ,,large ,,beams 7,forest ,service ,bul4 #ajh1 p4 #ef7 ---------------------------------------- ------------------- ,total ,per cent of total failing by ,,common ,,name number ----------------------------- ,,of ,,species of ,tension ,compression ,shear tests ---------------------------------------- --------------- ,longleaf pine3 green #ag #ah #bd #eh dry #i #bb #bb #ef ,douglas fir3 green #aia #bg #gb #a dry #ia #ai #gf #e ,shortleaf pine3 green #dh #bg #ef #ag dry #ac #ed #df ,western larch3 green #fb #bc #ga #f dry #eb #ed #ai #bg ,loblolly pine3 green #aaa #dj #ec #g dry #be #fj #ab #bh ,tamarack3 green #cj #cg #ec #aj dry #i #de #bb #cc ,western hemlock3 green #ci #ba #gd #e dry #dd #aa #ff #bc ,redwood3 green #bh #dc #ej #g dry #ab #hc #ag ,norway pine3 green #di #ah #gf #f dry #aj #cj #fj #aj ---------------------------------------- ------------------- ,,note4--,these tests were made on timbers ranging in cross section from #d x #aj to #h x #af1 and with a span of #ae feet4 ---------------------------------------- ------------------- ,,toughness3 ,,torsion ,toughness is a term applied to more than one property of wood4 ,thus wood that is difficult to split is said to be tough4 ,again1 a tough wood is one that will not rupture until it has deformed considerably under loads at or near its maximum strength1 or one which still hangs together after it has been ruptured and may be bent back and forth without breaking apart4 ,toughness includes flexibility and is the reverse of brittleness1 in that tough woods break gradually and give warning of failure4 ,tough woods offer great resistance to impact and will permit rougher treatment in manipulations attending manufacture and use4 ,toughness is dependent upon the strength1 cohesion1 quality1 length1 and arrangement of fibre1 and the pliability of the wood4 ,coniferous woods as a rule are not as tough as hardwoods1 of which hickory and elm are the best examples4 ,the torsion or twisting test is useful in determining the toughness of wood4 ,if the ends of a shaft are turned in opposite directions1 or one end is turned and the other is fixed1 all of the fibres except those at the axis tend to assume the form of helices4 7,see ,fig4 #ai47 ,the strain produced by torsion or twisting is essentially shear transverse and parallel to the fibres1 combined with longitudinal tension and transverse compression4 ,within the elastic limit the strains increase directly as the distance from the axis of the specimen4 ,the outer elements are subjected to tensile stresses1 and as they become twisted tend to compress those near the axis4 ,the elongated elements also contract laterally4 ,cross sections which were originally plane become warped4 ,with increasing strain the lateral adhesion of the outer fibres is destroyed1 allowing them to slide past each other1 and reducing greatly their power of resistance4 ,in this way the strains on the fibres nearer the axis are progressively increased until finally all of the elements are sheared apart4 ,it is only in the toughest materials that the full effect of this action can be observed4 7,see ,fig4 #bj47 ,brittle woods snap off suddenly with only a small amount of torsion1 and their fracture is irregular and oblique to the axis of the piece instead of frayed out and more nearly perpendicular to the axis as is the case with tough woods4 ,illustration3 ,,fig4 #ai4--,torsion of a shaft4 ,illustration3 ,,fig4 #bj4--;,effect of torsion on different grades of hickory4 ,photo by ,u4 ,s4 ,forest ,service4 ,,hardness ,the term hardness is used in two senses1 namely3 7#a7 resistance to indentation1 and 7#b7 resistance to abrasion or scratching4 ,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 floors1 paving blocks1 bearings1 and rollers4 ,while resistance to indentation is dependent mostly upon the density of the wood1 the wearing qualities may be governed by other factors such as toughness1 and the size1 cohesion1 and arrangement of the fibres4 ,in use for floors1 some woods tend to compact and wear smooth1 while others become splintery and rough4 ,this feature is affected to some extent by the manner in which the wood is sawed2 thus edge-grain pine flooring is much better than flat-sawn for uniformity of wear4 ---------------------------------------- --------------------------- ,,table ,,xii ---------------------------------------- --------------------------- ,,hardness ,,of #cb ,,woods ,,in ,,green ,,condition1 ,,as ,,indicated ,,by ,,the ,,load ,,required ,,to ,,imbed ,a #j4ddd-;,,inch ,,steel ,,ball ,,to ,,one-,,half ,,its ,,diameter 7,forest ,service ,cir4 #bac7 ---------------------------------------- --------------------------- ,,common ,,name ,,of ,,species ,average ,end ,radial ,tangential surface surface surface ---------------------------------------- ----------------------- ,pounds ,pounds ,pounds ,pounds ,hardwoods #a ,osage orange #a1iga #a1hch #b1cab #a1gfb #b ,honey locust #a1hea #a1hfb #a1hfj #a1hcb #c ,swamp white oak #a1agd #a1bje #a1bag #a1jii #d ,white oak #a1afd #a1ahc #a1afc #a1adg #e ,post oak #a1jii #a1aci #a1jfh #a1jha #f ,black oak #a1jfi #a1jic #a1jhc #a1jca #g ,red oak #a1jdc #a1ajg #a1jbj #a1jjb #h ,white ash #a1jdf #a1aba #a1jjj #a1jag #i ,beech #idb #a1jab #hig #iah #aj ,sugar maple #icg #iib #iah #ija #aa ,rock elm #iaj #ied #hhc #hic #ab ,hackberry #gii #hbi #gie #ggc #ac ,slippery elm #ghh #iai #geg #fhg #ad ,yellow birch #ggh #hbg #gfh #gci #ae ,tupelo #gch #had #fff #gcc #af ,red maple #fga #gff #fba #fbf #ag ,sycamore #fjh #ffd #efj #eii #ah ,black ash #eea #efe #edb #edf #ai ,white elm #dif #ecf #def #dig #bj ,basswood #bci #bgc #bbf #bag ,conifers #a ,longleaf pine #ecb #egd #ejb #eba #b ,douglas fir #daj #dae #cii #daf #c ,bald cypress #cij #dfj #cee #ced #d ,hemlock #chd #dfc #ced #ccd #e ,tamarack #chd #dja #chj #cgj #f ,red pine #cdg #cee #cde #cdj #g ,white fir #cdf #cha #cbb #ccd #h ,western yellow pine #cbh #ccd #cjg #cdb #i ,lodgepole pine #cah #caf #cah #cai #aj ,white pine #bii #cjd #bid #bii #aa ,engelmann pine #bff #bgb #bec #bgd #ab ,alpine fir #bda #bhd #bjc #bce ---------------------------------------- --------------------------- ,,note4--,black locust and hickory are not included in this table1 but their position would be near the head of the list4 ---------------------------------------- --------------------------- ,tests for either form of hardness are of comparative value only4 ,tests for indentation are commonly made by penetrations of the material with a steel punch or ball4#af ,tests for abrasion are made by wearing down wood with sandpaper or by means of a sand blast4 ,footnote #af3 ,see articles by ,gabriel ,janka listed in bibliography1 pages #aea-aeb4 ,,cleavability ,cleavability is the term used to denote the facility with which wood is split4 ,a splitting stress is one in which the forces act normally like a wedge4 7,see ,fig4 #ba47 ,the plane of cleavage is parallel to the grain1 either radially or tangentially4 ,illustration3 ,,fig4 #ba4--;,cleavage of highly elastic wood4 ,the cleft runs far ahead of the wedge4 ,this property of wood is very important in certain uses such as firewood1 fence rails1 billets1 and squares4 ,resistance to splitting or low cleavability is desirable where wood must hold nails or screws1 as in box-making4 ,wood usually splits more readily along the radius than parallel to the growth rings though exceptions occur1 as in the case of cross grain4 ,splitting involves transverse tension1 but only a portion of the fibres are under stress at a time4 ,a wood of little stiffness and strong cohesion across the grain is difficult to split1 while one with great stiffness1 such as longleaf pine1 is easily split4 ,the form of the grain and the presence of knots greatly affect this quality4 ---------------------------------------- ----- ,,table ,,xiii ---------------------------------------- ----- ,,cleavage ,,strength ,,of ,,small ,,clear ,,pieces ,,of #cb ,,woods ,,in ,,green ,,condition 7,forest ,service ,cir4 #bac7 ---------------------------------------- ----- ,when ,when ,,common ,,name surface of surface of ,,of ,,species failure is failure is radial tangential ---------------------------------------- --- ,lbs4 per ,lbs4 per sq4 inch sq4 inch ,hardwoods ,ash1 black #bge #bfj white #ccc #cdf ,bashwood #acj #afh ,beech #cci #ebg ,birch1 yellow #bid #bhg ,elm1 slippery #dja #dbd white #baj #bgj ,hackberry #dbb #dcf ,locust1 honey #eeb #faj ,maple1 red #big #ccj sugar #cgf #eac ,oak1 post #ced #dhg red #chj #dgj swamp white #dbh #ecf white #chb #deg yellow #cgi #dgj ,sycamore #bfe #dbe ,tupelo #bgg #chj ,conifers ,arborvit #adh #aci ,cypress1 bald #afg #aed ,fir1 alpine #acj #acc ,douglas #aci #abg white #ade #ahg ,hemlock #afh #aea ,pine1 lodgepole #adb #adj longleaf #ahg #ahj red #afa #aed sugar #afh #ahi western yellow #afb #ahg white #add #afj ,spruce1 ,engelmann #aaj #ace ,tamarack #afg #aei ---------------------------------------- ----- ,,part ,,ii ,,factors ,,affecting ,,the ,,mechanical ,,properties ,,of ,,wood ,,introduction ,wood is an organic product--a structure of infinite variation of detail and design4#ag ,it is on this account that no two woods are alike--in reality no two specimens from the same log are identical4 ,there are certain properties that characterize each species1 but they are subject to considerable variation4 ,oak1 for example1 is considered hard1 heavy1 and strong1 but some pieces1 even of the same species of oak1 are much harder1 heavier1 and stronger than others4 ,with hickory are associated the properties of great strength1 toughness1 and resilience1 but some pieces are comparatively weak and brash and ill-suited for the exacting demands for which good hickory is peculiarly adapted4 ,footnote #ag3 ,for details regarding the structure of wood see ,record1 ,samuel ,j43 ,identification of the economic woods of the ,united ,states4 ,new ,york1 ,john ,wiley ,sons1 #aiab4 ,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 stick4 ,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 average4 ,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 conclusions4 ,,rate ,,of ,,growth ,to understand the effect of variations in the rate of growth it is first necessary to know how wood is formed4 ,a tree increases in diameter by the formation1 between the old wood and the inner bark1 of new woody layers which envelop the entire stem1 living branches1 and roots4 ,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 annual rings4 ,these growth layers are made up of wood cells of various kinds1 but for the most part fibrous4 ,in timbers like pine1 spruce1 hemlock1 and other coniferous or softwood species the wood cells are mostly of one kind1 and as a result the material is much more uniform in structure than that of most hardwoods4 7,see ,frontispiece47 ,there are no vessels or pores in coniferous wood such as one sees so prominently in oak and ash1 for example4 7,see ,fig4 #bb47 ,illustration3 ,,fig4 #bb4--;,cross sections of a ring-porous hardwood 7white ash71 a diffuse-porous hardwood 7red gum71 and a non-porous or coniferous wood 7eastern hemlock74 ,x #cj4 ,photomicrographs by the author4 ,the structure of the hardwoods is more complex4 ,they are more or less filled with vessels1 in some cases 7oak1 chestnut1 ash7 quite large and distinct1 in others 7buckeye1 poplar1 gum7 too small to be seen plainly without a small hand lens4 ,in discussing such woods it is customary to divide them into two large classes--ring-porous and diffuse-porous4 7,see ,fig4 #bb47 ,in ring-porous species1 such as oak1 chestnut1 ash1 black locust1 catalpa1 mulberry1 hickory1 and elm1 the larger vessels or pores 7as cross sections of vessels are called7 become localized in one part of the growth ring1 thus forming a region of more or less open and porous tissue4 ,the rest of the ring is made up of smaller vessels and a much greater proportion of wood fibres4 ,these fibres are the elements which give strength and toughness to wood1 while the vessels are a source of weakness4 ,in diffuse-porous woods the pores are scattered throughout the growth ring instead of being collected in a band or row4 ,examples of this kind of wood are gum1 yellow poplar1 birch1 maple1 cottonwood1 basswood1 buckeye1 and willow4 ,some species1 such as walnut and cherry1 are on the border between the two classes1 forming a sort of intermediate group4 ,if one examines the smoothly cut end of a stick of almost any kind of wood1 he will note that each growth ring is made up of two more or less well-defined parts4 ,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 ring4 ,the inner portion was formed early in the season1 when growth was comparatively rapid and is known as early wood 7also spring wood72 the outer portion is the late wood1 being produced in the summer or early fall4 ,in soft pines there is not much contrast in the different parts of the ring1 and as a result the wood is very uniform in texture and is easy to work4 ,in hard pine1 on the other hand1 the late wood is very dense and is deep-colored1 presenting a very decided contrast to the soft1 straw-colored early wood4 7,see ,fig4 #bc47 ,in ring-porous woods each season's growth is always well defined1 because the large pores of the spring abut on the denser tissue of the fall before4 ,in the diffuse-porous1 the demarcation between rings is not always so clear and in not a few cases is almost1 if not entirely1 invisible to the unaided eye4 7,see ,fig4 #bb47 ,illustration3 ,,fig4 #bc4--;,cross section of longleaf pine showing several growth rings with variations in the width of the dark-colored late wood4 ,seven resin ducts are visible4 ,x #cc4 ,photomicrograph by ,u4,s4 ,forest ,service ,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 other1 and is therefore considerably darker4 ,the late wood of all species is denser than that formed early in the season1 hence the greater the proportion of late wood the greater the density and strength4 ,when examined under a microscope the cells of the late wood are seen to be very thick-walled and with very small cavities1 while those formed first in the season have thin walls and large cavities4 ,the strength is in the walls1 not the cavities4 ,in choosing a piece of pine where strength or stiffness is the important consideration1 the principal thing to observe is the comparative amounts of early and late wood4 ,the width of ring1 that is1 the number per inch1 is not nearly so important as the proportion of the late wood in the ring4 ,it is not only the proportion of late wood1 but also its quality1 that counts4 ,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 little4 ,one can judge comparative density1 and therefore to some extent weight and strength1 by visual inspection4 ,the conclusions of the ,u4,s4 ,forest ,service regarding the effect of rate of growth on the properties of ,douglas fir are summarized as follows3 #a4 ,in general1 rapidly grown wood 7less than eight rings per inch7 is relatively weak4 ,a study of the individual tests upon which the average points are based shows1 however1 that when it is not associated with light weight and a small proportion of summer wood1 rapid growth is not indicative of weak wood4 #b4 ,an average rate of growth1 indicated by from #ab to #af rings per inch1 seems to produce the best material4 #c4 ,in rates of growths lower than #af rings per inch1 the average strength of the material decreases1 apparently approaching a uniform condition above #bd rings per inch4 ,in such slow rates of growth the texture of the wood is very uniform1 and naturally there is little variation in weight or strength4 ,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 beams4 ,the analysis indicated conclusively that there was no such relation4 ,average rate of growth without consideration also of density1 therefore1 has little significance in grading structural timber4#ah ,this is because of the wide variation in the percentage of late wood in different parts of the cross section4 ,footnote #ah3 ,bul4 #hh3 ,properties and uses of ,douglas fir1 p4 #bi4 ,experiments seem to indicate that for most species there is a rate of growth which1 in general1 is associated with the greatest strength1 especially in small specimens4 ,for eight conifers it is as follows3#ai ,footnote #ai3 ,bul4 #ajh1 ,u4 ,s4 ,forest ,service3 ,tests of structural timbers1 p4 #cg4 ,rings per inch ,douglas fir #bd ,shortleaf pine #ab ,loblolly pine #f ,western larch #ah ,western hemlock #ad ,tamarack #bj ,norway pine #ah ,redwood #cj ,no satisfactory explanation can as yet be given for the real causes underlying the formation of early and late wood4 ,several factors may be involved4 ,in conifers1 at least1 rate of growth alone does not determine the proportion of the two portions of the ring1 for in some cases the wood of slow growth is very hard and heavy1 while in others the opposite is true4 ,the quality of the site where the tree grows undoubtedly affects the character of the wood formed1 though it is not possible to formulate a rule governing it4 ,in general1 however1 it may be said that where strength or ease of working is essential1 woods of moderate to slow growth should be chosen4 ,but in choosing a particular specimen it is not the width of ring1 but the proportion and character of the late wood which should govern4 ,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 properties4 ,this may be briefly summed up in the general statement that the more rapid the growth or the wider the rings of growth1 the heavier1 harder1 stronger1 and stiffer the wood4 ,this1 it must be remembered1 applies only to ring-porous woods such as oak1 ash1 hickory1 and others of the same group1 and is1 of course1 subject to some exceptions and limitations4 ,in ring-porous woods of good growth it is usually the middle portion of the ring in which the thick-walled1 strength-giving fibres are most abundant4 ,as the breadth of ring diminishes1 this middle portion is reduced so that very slow growth produces comparatively light1 porous wood composed of thin-walled vessels and wood parenchyma4 ,in good oak these large vessels of the early wood occupy from #f to #aj per cent of the volume of the log1 while in inferior material they may make up #be per cent or more4 ,the late wood of good oak1 except for radial grayish patches of small pores1 is dark colored and firm1 and consists of thick-walled fibres which form one-half or more of the wood4 ,in inferior oak1 such fibre areas are much reduced both in quantity and quality4 ,such variation is very largely the result of rate of growth4 ,wide-ringed wood is often called second-growth1 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 forest1 and in the manufacture of articles where strength is an important consideration such second-growth hardwood material is preferred4 ,this is particularly the case in the choice of hickory for handles and spokes4 ,here not only strength1 but toughness and resilience are important4 ,the results of a series of tests on hickory by the ,u4,s4 ,forest ,service show that the work or shock-resisting ability is greatest in wide-ringed wood that has from #e to #ad rings per inch1 is fairly constant from #ad to #ch rings1 and decreases rapidly from #ch to #dg rings4 ,the strength at maximum load is not so great with the most rapid-growing wood2 it is maximum with from #ad to #bj rings per inch1 and again becomes less as the wood becomes more closely ringed4 ,the natural deduction is that wood of first-class mechanical value shows from #e to #bj rings per inch and that slower growth yields poorer stock4 ,thus the inspector or buyer of hickory should discriminate against timber that has more than #bj rings per inch4 ,exceptions exist1 however1 in the case of normal growth upon dry situations1 in which the slow-growing material may be strong and tough4#bj ,footnote #bj3 ,bul4 #hj3 ,the commercial hickories1 pp4 #dh-ej4 ,the effect of rate of growth on the qualities of chestnut wood is summarized by the same authority as follows3 ,when the rings are wide1 the transition from spring wood to summer wood is gradual1 while in the narrow rings the spring wood passes into summer wood abruptly4 ,the width of the spring wood changes but little with the width of the annual ring1 so that the narrowing or broadening of the annual ring is always at the expense of the summer wood4 ,the narrow vessels of the summer wood make it richer in wood substance than the spring wood composed of wide vessels4 ,therefore1 rapid-growing specimens with wide rings have more wood substance than slow-growing trees with narrow rings4 ,since the more the wood substance the greater the weight1 and the greater the weight the stronger the wood1 chestnuts with wide rings must have stronger wood than chestnuts with narrow rings4 ,this agrees with the accepted view that sprouts 7which always have wide rings7 yield better and stronger wood than seedling chestnuts1 which grow more slowly in diameter4#ba ,footnote #ba3 ,bul4 #ec3 ,chestnut in southern ,maryland1 pp4 #bj-ba4 ,in diffuse-porous woods1 as has been stated1 the vessels or pores are scattered throughout the ring instead of collected in the early wood4 ,the effect of rate of growth is1 therefore1 not the same as in the ring-porous woods1 approaching more nearly the conditions in the conifers4 ,in general it may be stated that such woods of medium growth afford stronger material than when very rapidly or very slowly grown4 ,in many uses of wood1 strength is not the main consideration4 ,if ease of working is prized1 wood should be chosen with regard to its uniformity of texture and straightness of grain1 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 next4 ,,heartwood ,,and ,,sapwood ,examination of the end of a log of many species reveals a darker-colored inner portion--the heartwood1 surrounded by a lighter-colored zone--the sapwood4 ,in some instances this distinction in color is very marked2 in others1 the contrast is slight1 so that it is not always easy to tell where one leaves off and the other begins4 ,the color of fresh sapwood is always light1 sometimes pure white1 but more often with a decided tinge of green or brown4 ,sapwood is comparatively new wood4 ,there is a time in the early history of every tree when its wood is all sapwood4 ,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 leaves4 ,the more leaves a tree bears and the more thrifty its growth1 the larger the volume of sapwood required1 hence trees making rapid growth in the open have thicker sapwood for their size than trees of the same species growing in dense forests4 ,sometimes trees grown in the open may become of considerable size1 a foot or more in diameter1 before any heartwood begins to form1 for example1 in second-growth hickory1 or field-grown white and loblolly pines4 ,as a tree increases in age and diameter an inner portion of the sapwood becomes inactive and finally ceases to function4 ,this inert or dead portion is called heartwood1 deriving its name solely from its position and not from any vital importance to the tree1 as is shown by the fact that a tree can thrive with its heart completely decayed4 ,some1 species begin to form heartwood very early in life1 while in others the change comes slowly4 ,thin sapwood is characteristic of such trees as chestnut1 black locust1 mulberry1 ,osage orange1 and sassafras1 while in maple1 ash1 gum1 hickory1 hackberry1 beech1 and loblolly pine1 thick sapwood is the rule4 ,there is no definite relation between the annual rings of growth and the amount of sapwood4 ,within the same species the cross-sectional area of the sapwood is roughly proportional to the size of the crown of the tree4 ,if the rings are narrow1 more of them are required than where they are wide4 ,as the tree gets larger1 the sapwood must necessarily become thinner or increase materially in volume4 ,sapwood is thicker in the upper portion of the trunk of a tree than near the base1 because the age and the diameter of the upper sections are less4 ,when a tree is very young it is covered with limbs almost1 if not entirely1 to the ground1 but as it grows older some or all of them will eventually die and be broken off4 ,subsequent growth of wood may completely conceal the stubs which1 however1 will remain as knots4 ,no matter how smooth and clear a log is on the outside1 it is more or less knotty near the middle4 ,consequently the sapwood of an old tree1 and particularly of a forest-grown tree1 will be freer from knots than the heartwood4 ,since in most uses of wood1 knots are defects that weaken the timber and interfere with its ease of working and other properties1 it follows that sapwood1 because of its position in the tree1 may have certain advantages over heartwood4 ,it is really remarkable that the inner heartwood of old trees remains as sound as it usually does1 since in many cases it is hundreds of years1 and in a few instances thousands of years1 old4 ,every broken limb or root1 or deep wound from fire1 insects1 or falling timber1 may afford an entrance for decay1 which1 once started1 may penetrate to all parts of the trunk4 ,the larv of many insects bore into the trees and their tunnels remain indefinitely as sources of weakness4 ,whatever advantages1 however1 that sapwood may have in this connection are due solely to its relative age and position4 ,if a tree grows all its life in the open and the conditions of soil and site remain unchanged1 it will make its most rapid growth in youth1 and gradually decline4 ,the annual rings of growth are for many years quite wide1 but later they become narrower and narrower4 ,since each succeeding ring is laid down on the outside of the wood previously formed1 it follows that unless a tree materially increases its production of wood from year to year1 the rings must necessarily become thinner4 ,as a tree reaches maturity its crown becomes more open and the annual wood production is lessened1 thereby reducing still more the width of the growth rings4 ,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 alternate4 ,some trees1 such as southern oaks1 maintain the same width of ring for hundreds of years4 ,upon the whole1 however1 as a tree gets larger in diameter the width of the growth rings decreases4 ,it is evident that there may be decided differences in the grain of heartwood and sapwood cut from a large tree1 particularly one that is overmature4 ,the relationship between width of growth rings and the mechanical properties of wood is discussed under ,rate of ,growth4 ,in this connection1 however1 it may be stated that as a general rule the wood laid on late in the life of a tree is softer1 lighter1 weaker1 and more even-textured than that produced earlier4 ,it follows that in a large log the sapwood1 because of the time in the life of the tree when it was grown1 may be inferior in hardness1 strength1 and toughness to equally sound heartwood from the same log4 ,after exhaustive tests on a number of different woods the ,u4,s4 ,forest ,service concludes as follows3 ,sapwood1 except that from old1 overmature trees1 is as strong as heartwood1 other things being equal1 and so far as the mechanical properties go should not be regarded as a defect4#bb ,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 timber4 ,footnote #bb3 ,bul4 #ajh3 ,tests of structural timber1 p4 #ce4 ,in the study of the hickories the conclusion was3 ,there is an unfounded prejudice against the heartwood4 ,specifications place white hickory1 or sapwood1 in a higher grade than red hickory1 or heartwood1 though there is no inherent difference in strength4 ,in fact1 in the case of large and old hickory trees1 the sapwood nearest the bark is comparatively weak1 and the best wood is in the heart1 though in young trees of thrifty growth the best wood is in the sap4#bc ,the results of tests from selected pieces lying side by side in the same tree1 and also the average values for heartwood and sapwood in shipments of the commercial hickories without selection1 show conclusively that the transformation of sapwood into heartwood does not affect either the strength or toughness of the wood4444 ,it is true1 however1 that sapwood is usually more free from latent defects than heartwood4#bd ,footnote #bc3 ,bul4 #hj3 ,the commercial hickories1 p4 #ej4 ,footnote #bd3 ,loc4 cit4 ,specifications for paving blocks often require that longleaf pine be #ij per cent heart4 ,this is on the belief that sapwood is not only more subject to decay1 but is also weaker than heartwood4 ,in reality there is no sound basis for discrimination against sapwood on account of strength1 provided other conditions are equal4 ,it is true that sapwood will not resist decay as long as heartwood1 if both are untreated with preservatives4 ,it is especially so of woods with deep-colored heartwood1 and is due to infiltrations of tannins1 oils1 and resins1 which make the wood more or less obnoxious to decay-producing fungi4 ,if1 however1 the timbers are to be treated1 sapwood is not a defect2 in fact1 because of the relative ease with which it can be impregnated with preservatives it may be made more desirable than heartwood4#be ,footnote #be3 ,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 microscope1 nevertheless sapwood is generally decidedly different from heartwood in its physical properties4 ,it dries better and more easily than heartwood1 usually with less shrinkage and little checking or honeycombing4 ,this is especially the case with the more refractory woods1 such as white oaks and ,eucalyptus globulus and viminalis4 ,it is usually much more permeable to air1 even in green wood1 notably so in loblolly pine and even in white oak4 ,as already stated1 it is much more subject to decay4 ,the sapwood of white oak may be impregnated with creosote with comparative ease1 while the heartwood is practically impenetrable4 ,these facts indicate a difference in its chemical nature4--,h4,d4 ,tiemann4 ,in specifications for structural timbers reference is sometimes made to boxheart1 meaning the inclusion of the pith or centre of the tree within a cross section of the timber4 ,from numerous experiments it appears that the position of the pith does not bear any relation to the strength of the material4 ,since most season checks1 however1 are radial1 the position of the pith may influence the resistance of a seasoned beam to horizontal shear1 being greatest when the pith is located in the middle half of the section4#bf ,footnote #bf3 ,bul4 #ajh1 ,u4,s4 ,forest ,service1 p4 #cf4 ,,weight1 ,,density1 ,,and ,,specific ,,gravity ,from data obtained from a large number of tests on the strength of different woods it appears that1 other things being equal1 the crushing strength parallel to the grain1 fibre stress at elastic limit in bending1 and shearing strength along the grain of wood vary in direct proportion to the weight of dry wood per unit of volume when green4 ,other strength values follow different laws4 ,the hardness varies in a slightly greater ratio than the square of the density4 ,the work to the breaking point increases even more rapidly than the cube of density4 ,the modulus of rupture in bending lies between the first power and the square of the density4 ,this1 of course1 is true only in case the greater weight is due to increase in the amount of wood substance4 ,a wood heavy with resin or other infiltrated substance is not necessarily stronger than a similar specimen free from such materials4 ,if differences in weight are due to degree of seasoning1 in other words1 to the relative amounts of water contained1 the rules given above will of course not hold1 since strength increases with dryness4 ,but of given specimens of pine or of oak1 for example1 in the green condition1 the comparative strength may be inferred from the weight4 ,it is not permissible1 however1 to compare such widely different woods as oak and pine on a basis of their weights4#bg ,footnote #bg3 ,the oaks for some unknown reason fall below the normal strength for weight1 whereas the hickories rise above4 ,certain other woods also are somewhat exceptional to the normal relation of strength and density4 ,the weight of wood substance1 that is1 the material which composes the walls of the fibres and other cells1 is practically the same in all species1 whether pine1 hickory1 or cottonwood1 being a little greater than half again as heavy as water4 ,it varies slightly from beech sapwood1 #a4ej1 to ,douglas fir heartwood1 #a4eg1 averaging about #a4ee at #cj to #ce ,c41 in terms of water at its greatest density #d ,c4 ,the reason any wood floats is that the air imprisoned in its cavities buoys it up4 ,when this is displaced by water the wood becomes water-logged and sinks4 ,leaving out of consideration infiltrated substances1 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 substance4 ,density is merely the weight of a unit of volume1 as #ce pounds per cubic foot1 or #j4ef grams per cubic centimetre4 ,specific gravity or relative density is the ratio of the density of any material to the density of distilled water at #d ,c4 7#ci4b ,f474 ,a cubic foot of distilled water at #d ,c4 weighs #fb4dc pounds4 ,hence the specific gravity of a piece of wood with a density of #ce pounds is #ce _/ #fb4dc #j4efa4 ,to find the weight per cubic foot when the specific gravity is given1 simply multiply by #fb4dc4 ,thus1 #j4efa ,x #fb4dc #ce4 ,in the metric system1 since the weight of a cubic centimetre of pure water is one gram1 the density in grams per cubic centimetre has the same numerical value as the specific gravity4 ,since the amount of water in wood is extremely variable it usually is not satisfactory to refer to the density of green wood4 ,for scientific purposes the density of oven-dry wood is used2 that is1 the wood is dried in an oven at a temperature of #ajj;,c4 7#bab;,f47 until a constant weight is attained4 ,for commercial purposes the weight or density of air-dry or shipping-dry wood is used4 ,this is usually expressed in pounds per thousand board feet1 a board foot being considered as one-twelfth of a cubic foot4 ,wood shrinks greatly in drying from the green to the oven-dry condition4 7,see ,table ,,xiv47 ,consequently a block of wood measuring a cubic foot when green will measure considerably less when oven-dry4 ,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 wood4 ,in other words1 it is not the weight of a cubic foot of green wood minus the weight of the water which it contains4 ,since the latter is often a more convenient figure to use and much easier to obtain than the weight of oven-dry wood1 it is commonly expressed in tables of specific gravity or density of dry wood4 ---------------------------------------- ------------------------------------ ,,table ,,xiv ---------------------------------------- ------------------------------------ ,,specific ,,gravity1 ,,and ,,shrinkage ,,of #ea ,,american ,,woods 7,forest ,service ,cir4 #bac7 ---------------------------------------- ------------------------------------ ,specific gravity ,shrinkage from green to ,mois- oven-dry1 based on oven-dry condition ,,common ,,name ture ---------------------------------------- ------- ,,of ,,species content ,volume ,volume ,in ,tangen- when when volume ,radial tial green oven-dry ---------------------------------------- ------------------------------ ,per ,per ,per ,per cent cent cent cent ,hardwoods ,ash1 black #gg #j4dff white #ch 4#eej #j4fdj #ab4f #d4c #f4d #dg 4#eaf 4#eij #aa4g ,basswood #aaj 4#cae 4#cgd #ad4e #f4b #h4d ,beech #fa 4#eef 4#ffi #af4e #d4f #aj4e ,birch1 yellow #gb 4#ede 4#ffa #ag4j #g4i #i4j ,elm1 rock #df 4#egh slippery #eg 4#eda 4#fci #ae4e #e4a #i4i white #ff 4#dcj ,gum1 red #ga 4#dcd ,hackberry #ej 4#ejd 4#egf #ad4j #d4b #h4i ,hickory1 big shellbark #fd 4#fja #ag4f #g4d #aa4b #ee 4#fff #bj4i #g4i #ad4b bitternut #fe 4#fbd mockernut #fd 4#fjf #af4e #f4i #aj4d #eg 4#ffb #ah4i #h4d #aa4d #dh 4#fff nutmeg #gf 4#eeh pignut #ei 4#fbg #ae4j #e4f #i4h #ed 4#ffg #ae4c #f4c #i4e #ee 4#ffg #af4i #f4h #aj4i #eb 4#ffg #ba4b #h4e #ac4h shagbark #fe 4#fjh #af4j #f4e #aj4b #eh 4#fdf #ah4d #g4i #aa4d #fd 4#fag #fj 4#fec #ae4e #f4e #i4g water #gd 4#fcj ,locust1 honey #ec 4#fie 4#gei #h4f ,maple1 red #fi 4#eab sugar #eg 4#edf 4#fdc #ad4c #d4i #i4a #ef 4#egg ,oak1 post #fd 4#eij 4#gcb #af4j #e4g #aj4f red #hj 4#efh 4#ffj #ac4a #c4g #h4c swamp white #gd 4#fcg 4#gib #ag4g #e4e #aj4f tanbark #hh 4#ehe white #eh 4#eid 4#gjd #ae4h #f4b #h4c #fb 4#fjc 4#fif #ad4c #d4i #i4j #gh 4#fjj 4#gjh #af4j #d4h #i4b yellow #gg 4#egc 4#ffi #ad4b #d4e #i4g #hj 4#eej ,osage orange #ca 4#gfa 4#hch #h4i ,sycamore #ha 4#ded 4#ebf #ac4e #e4j #g4c ,tupelo #aba 4#dge 4#ede #ab4d #d4d #g4i ---------------------------------------- ------------------------------------ ---------------------------------------- ------------------------------------ ,,table ,,xiv 7,,cont47 ---------------------------------------- ------------------------------------ ,,specific ,,gravity1 ,,and ,,shrinkage ,,of #ea ,,american ,,woods 7,forest ,service ,cir4 #bac7 ---------------------------------------- ------------------------------------ ,specific gravity ,shrinkage from green to oven-dry1 based on oven-dry condition ,,common ,,name ---------------------------------------- ------- ,,of ,,species ,mois- ,volume ,volume ,in ,tangen- ture when when volume ,radial tial content green oven-dry ---------------------------------------- ------------------------------ ,per ,per ,per ,per cent cent cent cent ,conifers ,arborvit #ee 4#bic 4#cae #g4j #b4a #d4i ,cedar1 incense #hj 4#cfc ,cypress1 bald #gi 4#deb 4#eac #aa4e #c4h #f4j ,fir1 alpine #dg 4#cjf 4#cba #i4j #b4e #g4a amabilis #aag 4#chc ,douglas #cb 4#dah 4#deh #aj4i #c4g #f4f white #aef 4#cej 4#dcg #aj4b #c4d #g4j ,hemlock 7east47 #abi 4#cdj 4#cid #i4b #b4c #e4j ,pine1 lodgepole #dd 4#cgj 4#dae #aa4c #d4b #g4a #eh 4#cga 4#djg #aj4a #c4f #e4i longleaf #fc 4#ebh 4#eii #ab4h #f4j #g4f red or ,nor #ed 4#ddj 4#ejg #aa4e #d4e #g4b shortleaf #eb 4#ddg sugar #abc 4#cfj 4#chf #h4d #b4i #e4f west yellow #ih 4#cec 4#cie #i4b #d4a #f4d #abe 4#cgg 4#dcc #aa4e #d4c #g4c #ic 4#cia 4#dce #i4i #c4h #e4h white #gd 4#cfc 4#cia #g4h #b4b #e4i ,redwood #ha 4#ccd #fi 4#cff ,spruce1 ,engelmann #de 4#cbe 4#cei #aj4e #c4g #f4i #aef 4#bii 4#cce #aj4c #c4j #f4b red #ca 4#cif white #da 4#cah ,tamarack #eb 4#dia 4#eeh #ac4f #c4g #g4d ---------------------------------------- ------------------------------------ ,this weight divided by #fb4dc gives the specific gravity per green volume4 ,it is purely a fictitious quantity4 ,to convert this figure into actual density or specific gravity of the dry wood1 it is necessary to know the amount of shrinkage in volume4 ,if ,s is the percentage of shrinkage from the green to the oven-dry condition1 based on the green volume2 ,d1 the density of the dry wood per cubic foot while green2 and d the actual ,d density of oven-dry wood1 then ---------- d4 #a - 4#j ,s ,this relation becomes clearer from the following analysis3 ,taking ,v and ,w as the volume and weight1 respectively1 when green1 and v and w as the corresponding volume and weight when w ,w ,v - v oven-dry1 then1 d --- 2 ,d --- 2 ,s ------- ,x #ajj1 and v ,v ,v ,v - v s ------- ,x #ajj1 in which ,s is the percentage of shrinkage v from the green to the oven-dry condition1 based on the green volume1 and s the same based on the oven-dry volume4 ,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 intended1 since the shrinkage in volume may vary from #f to #ej per cent1 though in conifers it is usually about #aj per cent1 and in hardwoods nearer #ae per cent4 7,see ,table ,,xiv47 ,,color ,in species which show a distinct difference between heartwood and sapwood the natural color of heartwood is invariably darker than that of the sapwood1 and very frequently the contrast is conspicuous4 ,this is produced by deposits in the heartwood of various materials resulting from the process of growth1 increased possibly by oxidation and other chemical changes1 which usually have little or no appreciable effect on the mechanical properties of the wood4 7,see ,,heartwood ,,and ,,sapwood1 above47 ,some experiments#bh on very resinous longleaf pine specimens1 however1 indicate an increase in strength4 ,this is due to the resin which increases the strength when dry4 ,spruce impregnated with crude resin and dried is greatly increased in strength thereby4 ,footnote #bh3 ,bul4 #gj1 ,u4,s4 ,forest ,service1 p4 #ib2 also p4 #abf1 appendix4 ,since the late wood of a growth ring is usually darker in color than the early wood1 this fact may be used in judging the density1 and therefore the hardness and strength of the material4 ,this is particularly the case with coniferous woods4 ,in ring-porous woods the vessels of the early wood not infrequently appear on a finished surface as darker than the denser late wood1 though on cross sections of heartwood the reverse is commonly true4 ,except in the manner just stated the color of wood is no indication of strength4 ,abnormal discoloration of wood often denotes a diseased condition1 indicating unsoundness4 ,the black check in western hemlock is the result of insect attacks4#bi ,the reddish-brown streaks so common in hickory and certain other woods are mostly the result of injury by birds4#cj ,the discoloration is merely an indication of an injury1 and in all probability does not of itself affect the properties of the wood4 ,certain rot-producing fungi impart to wood characteristic colors which thus become criterions of weakness4 ,ordinary sap-staining is due to fungous growth1 but does not necessarily produce a weakening effect4#ca ,footnote #bi3 ,see ,burke1 ,h4,e43 ,black check in western hemlock4 ,cir4 ,no4 #fa1 ,u4,s4 ,bu4 ,entomology1 #aije4 ,footnote #cj3 ,see ,mc,atee1 ,w4,l43 ,woodpeckers in relation to trees and wood products4 ,bul4 ,no4 #ci1 ,u4,s4 ,biol4 ,survey1 #aiaa4 ,footnote #ca3 ,see ,von ,schrenck1 ,hermann3 ,the bluing and the red rot of the western yellow pine1 with special reference to the ,black ,hills forest reserve4 ,bul4 ,no4 #cf1 ,u4,s4 ,bu4 ,plant ,industry1 ,washington1 #aijc1 pp4 #ac-ad4 ,weiss1 ,howard1 and ,barnum1 ,charles ,t43 ,the prevention of sapstain in lumber4 ,cir4 #aib1 ,u4,s4 ,forest ,service1 ,washington1 #aiaa1 pp4 #af-ag4 ,,cross ,,grain ,cross grain is a very common defect in timber4 ,one form of it is produced in lumber by the method of sawing and has no reference to the natural arrangement of the wood elements4 ,thus 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 diagonal4 ,this is likely to occur where the logs have considerable taper1 and in this case may be produced if sawed parallel to the axis of growth instead of parallel to the growth rings4 ,lumber and timber with diagonal grain is always weaker than straight-grained material1 the extent of the defect varying with the degree of the angle the fibres make with the axis of the stick4 ,in the vicinity of large knots the grain is likely to be cross4 ,the defect is most serious where wood is subjected to flexure1 as in beams4 ,spiral grain is a very common defect in a tree1 and when excessive renders the timber valueless for use except in the round4 ,it is produced by the arrangement of the wood fibres in a spiral direction about the axis instead of exactly vertical4 ,timber with spiral grain is also known as torse wood4 ,spiral grain usually cannot be detected by casual inspection of a stick1 since it does not show in the so-called visible grain of the wood1 by which is commonly meant a sectional view of the annual rings of growth cut longitudinally4 ,it is accordingly very easy to allow spiral-grained material to pass inspection1 thereby introducing an element of weakness in a structure4 ,there are methods for readily detecting spiral grain4 ,the simplest is that of splitting a small piece radially4 ,it is necessary1 of course1 that the split be radial1 that is1 in a plane passing through the axis of the log1 and not tangentially4 ,in the latter case it is quite probable that the wood would split straight1 the line of cleavage being between the growth rings4 ,in inspection1 the elements to examine are the rays4 ,in the case of oak and certain other hardwoods these rays are so large that they are readily seen not only on a radial surface1 but on the tangential as well4 ,on the former they appear as flakes1 on the latter as short lines4 ,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-grained4 ,while they are not conspicuous in the softwoods1 they can be seen upon close scrutiny1 and particularly so if a small hand magnifier is used4 ,when wood has begun to dry and check it is very easy to see whether or not it is straight- or spiral-grained1 since the checks will for the most part follow along the rays4 ,if one examines a row of telephone poles1 for example1 he will probably find that most of them have checks running spirally around them4 ,if boards were sawed from such a pole after it was badly checked they would fall to pieces of their own weight4 ,the only way to get straight material would be to split it out4 ,it is for this reason that split billets and squares are stronger than most sawed material4 ,the presence of the spiral grain has little1 if any1 effect on the timber when it is used in the round1 but in sawed material the greater the pitch of the spiral the greater is the defect4 ,,knots ,knots are portions of branches included in the wood of the stem or larger branch4 ,branches originate as a rule from the central axis of a stem1 and while living increase in size by the addition of annual woody layers which are a continuation of those of the stem4 ,the included portion is irregularly conical in shape with the tip at the pith4 ,the direction of the fibre is at right angles or oblique to the grain of the stem1 thus producing local cross grain4 ,during the development of a tree most of the limbs1 especially the lower ones1 die1 but persist for a time--often for years4 ,subsequent layers of growth of the stem are no longer intimately joined with the dead limb1 but are laid around it4 ,hence dead branches produce knots which are nothing more than pegs in a hole1 and likely to drop out after the tree has been sawed into lumber4 ,in grading lumber and structural timber1 knots are classified according to their form1 size1 soundness1 and the firmness with which they are held in place4#cb ,footnote #cb3 ,see ,standard classification of structural timber4 ,yearbook ,am4 ,soc4 for ,testing ,materials1 #aiac1 pp4 #cjj-cjc4 ,contains three plates showing standard defects4 ,knots materially affect checking and warping1 ease in working1 and cleavability of timber4 ,they are defects which weaken timber and depreciate its value for structural purposes where strength is an important consideration4 ,the weakening effect is much more serious where timber is subjected to bending and tension than where under compression4 ,the extent to which knots affect the strength of a beam depends upon their position1 size1 number1 direction of fibre1 and condition4 ,a knot on the upper side is compressed1 while one on the lower side is subjected to tension4 ,the knot1 especially 7as is often the case7 if there is a season check in it1 offers little resistance to this tensile stress4 ,small1 knots1 however1 may be so located in a beam along the neutral plane as actually to increase the strength by tending to prevent longitudinal shearing4 ,knots in a board or plank are least injurious when they extend through it at right angles to its broadest surface4 ,knots which occur near the ends of a beam do not weaken it4 ,sound knots which occur in the central portion one-fourth the height of the beam from either edge are not serious defects4 ,extensive experiments by the ,u4,s4 ,forest ,service#cc indicate the following effects of knots on structural timbers3 ,footnote #cc3 ,bul4 #ajh1 pp4 #eb et seq4 7#a7 ,knots do not materially influence the stiffness of structural timber4 7#b7 ,only defects of the most serious character affect the elastic limit of beams4 ,stiffness and elastic strength are more dependent upon the quality of the wood fibre than upon defects in the beam4 7#c7 ,the effect of knots is to reduce the difference between the fibre stress at elastic limit and the modulus of rupture of beams4 ,the breaking strength is very susceptible to defects4 7#d7 ,sound knots do not weaken wood when subject to compression parallel to the grain4#cd ,footnote #cd3 ,bul4 #aae1 ,u4,s4 ,forest ,service3 ,mechanical properties of western hemlock1 p4 #bj4 ,,frost ,,splits ,a common defect in standing timber results from radial splits which extend inward from the periphery of the tree1 and almost1 if not always1 near the base4 ,it is most common in trees which split readily1 and those with large rays and thin bark4 ,the primary cause of the splitting is frost1 and various theories have been advanced to explain the action4 ,r4 ,hartig#ce believes that freezing forces out a part of the imbibition water of the cell walls1 thereby causing the wood to shrink1 and if the interior layers have not yet been cooled1 tangential strains arise which finally produce radial clefts4 ,footnote #ce3 ,hartig1 ,r43 ,the diseases of trees 7trans4 by ,somerville and ,ward71 ,london and ,new ,york1 #ahid1 pp4 #bhb-bid4 ,another theory holds that the water is not driven out of the cell walls1 but that difference in temperature conditions of inner and outer layers is itself sufficient to set up the strains1 resulting in splitting4 ,an air temperature of #ad;,f4 or less is considered necessary to produce frost splits4 ,a still more recent theory is that of ,busse#cf who considers the mechanical action of the wind a very important factor4 ,he observed3 7a7 ,frost splits sometimes occur at higher temperatures than #ad;,f4 7b7 ,most splits take place shortly before sunrise1 i4e41 at the time of lowest air and soil temperature2 they are never heard to take place at noon1 afternoon1 or evening4 7c7 ,they always occur between two roots or between the collars of two roots1 7d7 ,they are most frequent in old1 stout-rooted1 broad-crowned trees2 in younger stands it is always the stoutest members that are found with frost splits1 while in quite young stands they are altogether absent1 7e7 ,trees on wet sites are most liable to splits1 due to difference in wood structure1 just as difference in wood structure makes different species vary in this regard4 7f7 ,frost splits are most numerous less than three feet above the ground4 ,footnote #cf3 ,busse1 ,w43 ,frost-1 ,ring- und ,kernrisse4 ,forstwiss4 ,centralb41 ,,xxxii1 #b1 #aiaj1 pp4 #gd-ha4 ,when a tree is swayed by the wind the roots are counteracting forces1 and the wood fibres are tested in tension and compression by the opposing forces2 where the roots exercise tension stresses most effectively the effect of compression stresses is at a minimum2 only where the pressure is in excess of the tension1 i4e41 between the roots1 can a separation of the fibre result4 ,hence1 when by frost a tension on the entire periphery is established1 and the wind localizes additional strains1 failure occurs4 ,the stronger the compression and tension1 the severer the strains and the oftener failures occur4 ,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 sufficient4 ,frost splits may heal over temporarily1 but usually open up again during the following winter4 ,the presence of old splits is often indicated by a ridge of callous1 the result of the cambium's effort to occlude the wound4 ,frost splits not only affect the value of lumber1 but also afford an entrance into the living tree for disease and decay4 ,,shakes1 ,,galls1 ,,pitch ,,pockets ,heart shake occurs in nearly all overmature timber1 being more frequent in hardwoods 7especially oak7 than in conifers4 ,in typical heart shake the centre of the hole shows indications of becoming hollow and radial clefts of varying size extend outward from the pith1 being widest inward4 ,it frequently affects only the butt log1 but may extend to the entire hole and even the larger branches4 ,it usually results from a shrinkage of the heartwood due probably to chemical changes in the wood4 ,when it consists of a single cleft extending across the pith it is termed simple heart shake4 ,shake of this character in straight-grained trees affects only one or two central boards when cut into lumber1 but in spiral-grained timber the damage is much greater4 ,when shake consists of several radial clefts it is termed star shake4 ,in some instances one or more of these clefts may extend nearly to the bark4 ,in felled or converted timber clefts due to heart shake may be distinguished from seasoning cracks by the darker color of the exposed surfaces4 ,such clefts1 however1 tend to open up more and more as the timber seasons4 ,cup or ring shake results from the pulling apart of two or more growth rings4 ,it is one of the most serious defects to which sound timber is subject1 as it seriously reduces the technical properties of wood4 ,it is very common in sycamore and in western larch1 particularly in the butt portion4 ,its occurrence is most frequent at the junction of two growth layers of very unequal thickness4 ,consequently it is likely to occur in trees which have grown slowly for a time1 then abruptly increased1 due to improved conditions of light and food1 as in thinning4 ,old timber is more subject to it than young trees4 ,the damage is largely confined to the butt log4 ,cup shake is often associated with other forms of shake1 and not infrequently shows traces of decay4 ,the causes of cup shake are uncertain4 ,the swaying action of the wind may result in shearing apart the growth layers1 especially in trees growing in exposed places4 ,frost may in some instances be responsible for cup shake or at least a contributing factor1 although trees growing in regions free from frost often have ring shake4 ,shrinkage of the heartwood may be concentric as well as radial in its action1 thus producing cup shake instead of1 or in connection with1 heart shake4 ,a local defect somewhat similar in effect to cup shake is known as rind gall4 ,if the cambium layer is exposed by the removal of the entire bark or rind it will die4 ,subsequent growth over the damaged portion does not cohere with the wood previously formed by the old cambium4 ,the defect resulting is termed rind gall4 ,the most common causes of it are fire1 gnawing1 blazing1 chipping1 sun scald1 lightning1 and abrasions4 ,heart break is a term applied to areas of compression failure along the grain found in occasional logs4 ,sometimes these breaks are invisible until the wood is manufactured into the finished article4 ,the occurrence of this defect is mostly limited to the dense hardwoods1 such as hickory and to heavy tropical species4 ,it is the source of considerable loss in the fancy veneer industry1 as the veneer from valuable logs so affected drops to pieces4 ,the cause of heart break is not positively known4 ,it is highly probable1 however1 that when the tree is felled the trunk strikes across a rock or another log1 and the impact causes actual failure in the log as in a beam4 ,resin or pitch pockets are of common occurrence in the wood of larch1 spruce1 fir1 and especially of longleaf and other hard pines4 ,they are due to accumulations of resin in openings between adjacent layers of growth4 ,they are more frequent in trees growing alone than in those of dense stands4 ,the pockets are usually a few inches in greatest dimension and affect only one or two growth layers4 ,they are hidden until exposed by the saw1 rendering it impossible to cut lumber with reference to their position4 ,often several boards are damaged by a single pocket4 ,in grading lumber1 pitch pockets are classified as small1 standard1 and large1 depending upon their width and length4 ,,insect ,,injuries#cg ,footnote #cg3 ,for detailed information regarding insect injuries1 the reader is referred to the various publications of the ,u4,s4 ,bureau of ,entomology1 ,washington1 ,d4,c4 ,the larv of many insects are destructive to wood4 ,some attack the wood of living trees1 others only that of felled or converted material4 ,every hole breaks the continuity of the fibres and impairs the strength1 and if there are very many of them the material may be ruined for all purposes where strength is required4 ,some of the most common insects attacking the wood of living trees are the oak timber worm1 the chestnut timber worm1 carpenter worms1 ambrosia beetles1 the locust borer1 turpentine beetles and turpentine borers1 and the white pine weevil4 ,the insect injuries to forest products may be classed according to the stage of manufacture of the material4 ,thus round timber with the bark on1 such as poles1 posts1 mine props1 and sawlogs1 is subject to serious damage by the same class of insects as those mentioned above1 particularly by the round-headed borers1 timber worms1 and ambrosia beetles4 ,manufactured unseasoned products are subject to damage from ambrosia beetles and other wood borers4 ,seasoned hardwood lumber of all kinds1 rough handles1 wagon stock1 etc41 made partially or entirely of sapwood1 are often reduced in value from #aj to #ij per cent by a class of insects known as powder-post beetles4 ,finished hardwood products such as handles1 wagon1 carriage and machinery stock1 especially if ash or hickory1 are often destroyed by the powder-post beetles4 ,construction timbers in buildings1 bridges and trestles1 cross-ties1 poles1 mine props1 fence posts1 etc41 are sometimes seriously injured by wood-boring larv1 termites1 black ants1 carpenter bees1 and powder-post beetles1 and sometimes reduced in value from #aj to #ajj per cent4 ,in tropical countries termites are a very serious pest in this respect4 ,,marine ,,wood-,,borer ,,injuries ,vast amounts of timber used for piles in wharves and other marine structures are constantly being destroyed or seriously injured by marine borers4 ,almost invariably they are confined to salt water1 and all the woods commonly used for piling are subject to their attacks4 ,there are two genera of mollusks1 ,xylotrya and ,teredo1 and three of crustaceans1 ,limnoria1 ,chelura1 and ,sphoeroma1 that do serious damage in many places along both the ,atlantic and ,pacific coasts4 ,these mollusks1 which are popularly known as shipworms1 are much alike in structure and mode of life4 ,they attack the exposed surface of the wood and immediately begin to bore4 ,the tunnels1 often as large as a lead pencil1 extend usually in a longitudinal direction and follow a very irregular1 tangled course4 ,hard woods are apparently penetrated as readily as soft woods1 though in the same timber the softer parts are preferred4 ,the food consists of infusoria and is not obtained from the wood substance4 ,the sole object of boring into the wood is to obtain shelter4 ,although shipworms can live in cold water they thrive best and are most destructive in warm water4 ,the length of time required to destroy an average barked1 unprotected pine pile on the ,atlantic coast south from ,chesapeake ,bay and along the entire ,pacific coast varies from but one to three years4 ,of the crustacean borers1 ,limnoria1 or the wood louse1 is the only one of great importance1 although ,sphoeroma is reported destructive in places4 ,limnoria is about the size of a grain of rice and tunnels into the wood for both food and shelter4 ,the galleries extend inward radially1 side by side1 in countless numbers1 to the depth of about one-half inch4 ,the thin wood partitions remaining are destroyed by wave action1 so that a fresh surface is exposed to attack4 ,both hard and soft woods are damaged1 but the rate is faster in the soft woods or softer portions of a wood4 ,timbers seriously attacked by marine borers are badly weakened or completely destroyed4 ,if the original strength of the material is to be preserved it is necessary to protect the wood from the borers4 ,this is sometimes accomplished by proper injection of creosote oil1 and more or less successfully by the use of various kinds of external coatings4#ch ,no treatment1 however1 has proved entirely satisfactory4 ,footnote #ch3 ,see ,smith1 ,c4 ,stowell3 ,preservation of piling against marine wood borers4 ,cir4 #abh1 ,u4,s4 ,forest ,service1 #aijh1 pp4 #ae4 ,,fungous ,,injuries#ci ,footnote #ci3 ,see ,von ,schrenck1 ,h43 ,the decay of timber and methods of preventing it4 ,bul4 #ad1 ,u4,s4 ,bu4 ,plant ,industry1 ,washington1 ,d4,c41 #aijb4 ,also ,buls4 #cb1 #aad1 #bad1 #bff4 ,meineoke1 ,e4,p43 ,forest tree diseases common in ,california and ,nevada1 ,u4,s4 ,forest ,service1 ,washington1 ,d4,c41 #aiad4 ,hartig1 ,r43 ,the diseases of trees4 ,london and ,new ,york1 #ahid4 ,fungi are responsible for almost all decay of wood4 ,so far as known1 all decay is produced by living organisms1 either fungi or bacteria4 ,some species attack living trees1 sometimes killing them1 or making them hollow1 or in the case of pecky cypress and incense cedar filling the wood with galleries like those of boring insects4 ,a much larger variety work only in felled or dead wood1 even after it is placed in buildings or manufactured articles4 ,in any case the process of destruction is the same4 ,the mycelial threads penetrate the walls of the cells in search of food1 which they find either in the cell contents 7starches1 sugars1 etc471 or in the cell wall itself4 ,the breaking down of the cell walls through the chemical action of so-called enzymes secreted by the fungi follows1 and the eventual product is a rotten1 moist substance crumbling readily under the slightest pressure4 ,some species remove the ligneous matter and leave almost pure cellulose1 which is white1 like cotton2 others dissolve the cellulose1 leaving a brittle1 dark brown mass of ligno-cellulose4 ,fungi 7such as the bluing fungus7 which merely stain wood usually do not affect its mechanical properties unless the attacks are excessive4 ,it is evident1 then1 that the action of rot-causing fungi is to decrease the strength of wood1 rendering it unsound1 brittle1 and dangerous to use4 ,the most dangerous kinds are the so-called dry-rot fungi which work in many kinds of lumber after it is placed in the buildings4 ,they are particularly to be dreaded because unseen1 working as they do within the walls or inside of casings4 ,several serious wrecks of large buildings have been attributed to this cause4 ,it is stated#dj that in the three years 7#aiaa-aiac7 more than #ajj1jjj was required to repair damage due to dry rot4 ,footnote #dj3 ,dry rot in factory timbers1 by ,inspection ,dept4 ,associated ,factory ,mutual ,fire ,insurance ,cos41 #ca ,milk ,street1 ,boston1 #aiac4 ,dry rot develops best at #ge;,f4 and is said to be killed by a temperature of #aaj;,f4#da ,fully #gj per cent humidity is necessary in the air in which a timber is surrounded for the growth of this fungus1 and probably the wood must be quite near its fibre saturation condition4 ,nevertheless ,merulius lacrymans 7one of the most important species7 has been found to live four years and eight months in a dry condition4#db ,thorough kiln-drying will kill this fungus1 but will not prevent its redevelopment4 ,antiseptic treatment1 such as creosoting1 is the best prevention4 ,footnote #da3 ,falck1 ,richard3 ,die ,meruliusfale des ,bauholzes1 ,hausschwammforschungen1 #f4 ,heft41 ,jena1 #aiab4 ,footnote #db3 ,mez1 ,carl3 ,der ,hausschwamm4 ,dresden1 #aijh1 p4 #fc4 ,all fungi require moisture and air#dc for their growth4 ,deprived of either of these the fungus dies or ceases to develop4 ,just what degree of moisture in wood is necessary for the dry-rot fungus has not been determined1 but it is evidently considerably above that of thoroughly air-dry timber1 probably more than #ae per cent moisture4 ,hence the importance of free circulation of air about all timbers in a building4 ,footnote #dc3 ,a culture of fungus placed in a glass jar and the air pumped out ceases to grow1 but will start again as soon as oxygen is admitted4 ,warmth is also conducive to the growth of fungi1 the most favorable temperature being about #ij;,f4 ,they cannot grow in extreme cold1 although no degree of cold such as occurs naturally will kill them4 ,on the other hand1 high temperature will kill them1 but the spores may survive even the boiling temperature4 ,mould fungus has been observed to develop rapidly at #acj;,f4 in a dry kiln in moist air1 a condition under which an animal cannot live more than a few minutes4 ,this fungus was killed1 however1 at about #adj or #ade;,f4#dd ,footnote #dd3 ,experiments in kiln-drying ,eucalyptus in ,berkeley1 ,u4,s4 ,forest ,service4 ,the fungus 7,endothia parasitica ,and47 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 sapwood4#de ,footnote #de3 ,see ,anderson1 ,paul ,j43 ,the morphology and life history of the chestnut blight fungus4 ,bul4 ,no4 #g1 ,penna4 ,chestnut ,tree ,blight ,com41 ,harrisburg1 #aiad1 p4 #ag4 ,,parasitic ,,plant ,,injuries4#df ,footnote #df3 ,see ,york1 ,harlan ,h43 ,the anatomy and some of the biological aspects of the ,american mistletoe4 ,bul4 #abj1 ,sci4 ,ser4 ,no4 #ac1 ,univ4 of ,texas1 ,austin1 #aiji4 ,bray1 ,wm4 ,l43 ,the mistletoe pest in the ,southwest4 ,bul4 #aff1 ,u4,s4 ,bu4 ,plant ,ind41 ,washington1 #aiaj4 ,meinecke1 ,e4,p43 ,forest tree diseases common in ,california and ,nevada4 ,u4,s4 ,forest ,service1 ,washington1 #aiad1 pp4 #ed-eh4 ,the most common of the higher parasitic plants damaging timber trees are mistletoes4 ,many species of deciduous trees are attacked by the common mistletoe 7,phoradendron flavescens74 ,it is very prevalent in the ,south and ,southwest and when present in sufficient quantity does considerable damage4 ,there is also a considerable number of smaller mistletoes belonging to the genus ,razoumofskya 7,arceuthobium7 which are widely distributed throughout the country1 and several of them are common on coniferous trees in the ,rocky ,mountains and along the ,pacific coast4 ,one effect of the common mistletoe is the formation of large swellings or tumors4 ,often the entire tree may become stunted or distorted4 ,the western mistletoe is most common on the branches1 where it produces witches' broom4 ,it frequently attacks the trunk as well1 and boards cut from such trees are filled with long1 radial holes which seriously damage or destroy the value of the timber affected4 ,,locality ,,of ,,growth ,the data available regarding the effect of the locality of growth upon the properties of wood are not sufficient to warrant definite conclusions4 ,the subject has1 however1 been kept in mind in many of the ,u4,s4 ,forest ,service timber tests and the following quotations are assembled from various reports3 ,in both the ,cuban and longleaf pine the locality where grown appears to have but little influence on weight or strength1 and there is no reason to believe that the longleaf pine from one ,state is better than that from any other1 since such variations as are claimed can be found on any #dj-;acre lot of timber in any ,state4 ,but with loblolly and still more with shortleaf this seems not to be the case4 ,being widely distributed over many localities different in soil and climate1 the growth of the shortleaf pine seems materially influenced by location4 ,the wood from the southern coast and gulf region and even ,arkansas is generally heavier than the wood from localities farther north4 ,very light and fine-grained wood is seldom met near the southern limit of the range1 while it is almost the rule in ,missouri1 where forms resembling the ,norway pine are by no means rare4 ,the loblolly1 occupying both wet and dry soils1 varies accordingly4 ,cir4 ,no4 #ab1 p4 #f4 444 ,it is clear that as all localities have their heavy and their light timber1 so they all share in strong and weak1 hard and soft material1 and the difference in quality of material is evidently far more a matter of individual variation than of soil or climate4 ,ibid41 p4#bb ,a representative committee of the ,carriage ,builders' ,association had publicly declared that this important industry could not depend upon the supplies of southern timber1 as the oak grown in the ,south lacked the necessary qualities demanded in carriage construction4 ,without experiment this statement could be little better than a guess1 and was doubly unwarranted1 since it condemned an enormous amount of material1 and one produced under a great variety of conditions and by at least a dozen species of trees1 involving1 therefore1 a complexity of problems difficult enough for the careful investigator1 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 world4 ,a number of samples were at once collected 7part of them supplied by the carriage builders' committee71 and the fallacy of the broad statement mentioned was fully demonstrated by a short series of tests and a more extensive study into structure and weight of these materials4 ,from these tests it appears that pieces of white oak from ,arkansas excelled well-selected pieces from ,connecticut1 both in stiffness and endwise compression 7the two most important forms of resistance74 ,report upon the forestry investigations of the ,u4,s4,d4,a4 #ahgg-ahih1 p4 #cca4 ,see also ,rep4 of ,div4 of ,for41 #ahij1 p4 #bji4 ,in some regions there are many small1 stunted hickories1 which most users will not touch4 ,they have narrow sap1 are likely to be birdpecked1 and show very slow growth4 ,yet five of these trees from a steep1 dry south slope in ,west ,virginia had an average strength fully equal to that of the pignut from the better situation1 and were superior in toughness1 the work to maximum load being #cf4h as against #ca4b for pignut4 ,the trees had about twice as many rings per inch as others from better situations4 ,this1 however1 is not very significant1 as trees of the same species1 age1 and size1 growing side by side under the same conditions of soil and situation1 show great variation in their technical value4 ,it is hard to account for this difference1 but it seems that trees growing in wet or moist situations are rather inferior to those growing on fresher soil2 also1 it is claimed by many hickory users that the wood from limestone soils is superior to that from sandy soils4 ,one of the moot questions among hickory men is the relative value of northern and southern hickory4 ,the impression prevails that southern hickory is more porous and brash than hickory from the north4 ,the tests 444 indicate that southern hickory is as tough and strong as northern hickory of the same age4 ,but the southern hickories have a greater tendency to be shaky1 and this results in much waste4 ,in trees from southern river bottoms the loss through shakes and grub-holes in many cases amounts to as much as #ej per cent4 ,it is clear1 therefore1 that the difference in northern and southern hickory is not due to geographic location1 but rather to the character of timber that is being cut4 ,nearly all of that from southern river bottoms and from the ,cumberland ,mountains is from large1 old-growth trees2 that from the north is from younger trees which are grown under more favorable conditions1 and it is due simply to the greater age of the southern trees that hickory from that region is lighter and more brash than that from the north4 ,bul4 #hj1 pp4 #eb-ee4 ,,season ,,of ,,cutting ,it is generally believed that winter-felled timber has decided advantages over that cut at other seasons of the year1 and to that cause alone are frequently ascribed much greater durability1 less liability to check and split1 better color1 and even increased strength and toughness4 ,the conclusion from the various experiments made on the subject is that while the time of felling may1 and often does1 affect the properties of wood1 such result is due to the weather conditions rather than to the condition of the wood4 ,there are two phases of this question4 ,one is concerned with the physiological changes which might take place during the year in the wood of a living tree4 ,the other deals with the purely physical results due to the weather1 as differences in temperature1 humidity1 moisture1 and other features to be mentioned later4 ,those who adhere to the first view maintain that wood cut in summer is quite different in composition from that cut in winter4 ,one opinion is that in summer the sap is up1 while in winter it is down1 consequently winter-felled timber is drier4 ,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 winter4 ,again it is sometimes asserted that wood is actually denser in winter than in summer1 as part of the wood substance is dissolved out in the spring and used for plant food1 being restored in the fall4 ,it is obvious that such views could apply only to sapwood1 since it alone is in living condition at the time of cutting4 ,heartwood is dead wood and has almost no function in the existence of the tree other than the purely mechanical one of support4 ,heartwood does undergo changes1 but they are gradual and almost entirely independent of the seasons4 ,sapwood might reasonably be expected to respond to seasonal changes1 and to some extent it does4 ,just beneath the bark there is a thin layer of cells which during the growing season have not attained their greatest density4 ,with the exception of this one annual ring1 or portion of one1 the density of the wood substance of the sapwood is nearly the same the year round4 ,slight variations may occur due to impregnation with sugar and starch in the winter and its dissolution in the growing season4 ,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 growth4 ,the popular belief that sap is up in the spring and summer and is down in the winter has not been substantiated by experiment4 ,there are seasonal differences in the composition of sap1 but so far as the amount of sap in a tree is concerned there is fully as much1 if not more1 during the winter than in summer4 ,winter-cut wood is not drier1 to begin with1 than summer-felled--in reality1 it is likely to be wetter4#dg ,footnote #dg3 ,see ,record1 ,s4,j43 ,sap in relation to the properties of wood4 ,proc4 ,am4 ,wood ,preservers' ,assn41 ,baltimore1 ,md41 #aiac1 pp4 #afj-aff4 ,kempfer1 ,wm4 ,h43 ,the air-seasoning of timber4 ,in ,bul4 #afa1 ,am4 ,ry4 ,eng4 ,assn41 #aiac1 p4 #bad4 ,the important consideration in regard to this question is the series of circumstances attending the handling of the timber after it is felled4 ,wood dries more rapidly in summer than in winter1 not because there is less moisture at one time than another1 but because of the higher temperature in summer4 ,this greater heat is often accompanied by low humidity1 and conditions are favorable for the rapid removal of moisture from the exposed portions of wood4 ,wood dries by evaporation1 and other things being equal1 this will proceed much faster in hot weather than in cold4 ,it is a matter of common observation that when wood dries it shrinks1 and if shrinkage is not uniform in all directions the material pulls apart1 causing season checks4 7,see ,fig4 #bg47 ,if evaporation proceeds more rapidly on the outside than inside1 the greater shrinkage of the outer portions is bound to result in many checks1 the number and size increasing with the degree of inequality of drying4 ,in cold weather1 drying proceeds slowly but uniformly1 thus allowing the wood elements to adjust themselves with the least amount of rupturing4 ,in summer1 drying proceeds rapidly and irregularly1 so that material seasoned at that time is more likely to split and check4 ,there is less danger of sap rot when trees are felled in winter because the fungus does not grow in the very cold weather1 and the lumber has a chance to season to below the danger point before the fungus gets a chance to attack it4 ,if the logs in each case could be cut into lumber immediately after felling and given exactly the same treatment1 for example1 kiln-dried1 no difference due to the season of cutting would be noted4 ,,water ,,content#dh ,footnote #dh3 ,see ,tiemann1 ,h4,d43 ,effect of moisture upon the strength and stiffness of wood4 ,bul4 #gj1 ,u4,s4 ,forest ,service1 ,washington1 ,d4,c41 #aijf2 also ,cir4 #ajh1 #aijg4 ,water occurs in living wood in three conditions1 namely3 7#a7 in the cell walls1 7#b7 in the protoplasmic contents of the cells1 and 7#c7 as free water in the cell cavities and spaces4 ,in heartwood it occurs only in the first and last forms4 ,wood that is thoroughly air-dried retains from #h to #af per cent of water in the cell walls1 and none1 or practically none1 in the other forms4 ,even oven-dried wood retains a small percentage of moisture1 but for all except chemical purposes1 may be considered absolutely dry4 ,the general effect of the water content upon the wood substance is to render it softer and more pliable4 ,a similar effect of common observation is in the softening action of water on rawhide1 paper1 or cloth4 ,within certain limits the greater the water content the greater its softening effect4 ,drying produces a decided increase in the strength of wood1 particularly in small specimens4 ,an extreme example is the case of a completely dry spruce block two inches in section1 which will sustain a permanent load four times as great as that which a green block of the same size will support4 ,the greatest increase due to drying is in the ultimate crushing strength1 and strength at elastic limit in endwise compression2 these are followed by the modulus of rupture1 and stress at elastic limit in cross-bending1 while the modulus of elasticity is least affected4 ,these ratios are shown in ,table ,,xv1 but it is to be noted that they apply only to wood in a much drier condition than is used in practice4 ,for air-dry wood the ratios are considerably lower1 particularly in the case of the ultimate strength and the elastic limit4 ,stiffness 7within the elastic limit71 while following a similar law1 is less affected4 ,in the case of shear parallel to the grain1 the general effect of drying is to increase the strength1 but this is often offset by small splits and checks caused by shrinkage4 ---------------------------------------- ------------------------------ ,,table ,,xv ---------------------------------------- ------------------------------ ,,effect ,,of ,,drying ,,on ,,the ,,mechanical ,,properties ,,of ,,wood1 ,,shown ,,in ,,ratio ,,of ,,increase ,,due ,,to ,,reducing ,,moisture ,,content ,,from ,,the ,,green ,,condition ,,to ,,kiln-,,dry 7#c4e ,,per ,,cent7 7,forest ,service ,bul4 #gj1 p4 #hi7 ---------------------------------------- ------------------------------ ,,kind ,,of ,,strength ,longleaf ,spruce ,chestnut pine ---------------------------------------- --------------------------- 7#a7 7#b7 7#a7 7#b7 7#a7 7#b7 ,crushing strength parallel to grain #b4hi #b4fj #c4ga #c4da #b4hc #b4ee ,elastic limit in compression parallel to grain #b4fj #b4cd #c4hj #c4di #b4dj #b4bf ,modulus of rupture in bending #b4ej #b4bj #b4ha #b4ej #b4ji #a4hb ,stress at elastic limit in bending #b4ij #b4ee #b4ij #b4eh #b4cj #b4jj ,crushing strength at right angles to grain #b4eh #b4dh ,shearing strength parallel to grain #b4ja #a4ia #b4jc #a4ie #a4ee #a4dg ,modulus of elasticity in compression parallel to grain #a4fc #a4dg #b4bf #b4jh #a4dc #a4bi ,modulus of elasticity in bending #a4ei #a4ce #a4dc #a4bc #a4dd #a4ba ---------------------------------------- ------------------------------ ,,note4--,the figures in the first column show the relative increase in strength between a green specimen and a kiln-dry specimen of equal size4 ,the figures in the second column show the relative increase of strength of the same block after being dried from a green condition to #c4e per cent moisture1 correction having been made for shrinkage4 ,that is1 in the first column the strength values per actual unit of area are used2 in the second the values per unit of area of green wood which shrinks to smaller size when dried4 ,see also ,cir4 #ajh1 ,fig4 #a1 p4 #h4 ---------------------------------------- ------------------------------ ,the moisture content has a decided bearing also upon the manner in which wood fails4 ,in compression tests on very dry specimens the entire piece splits suddenly into pieces before any buckling takes place 7see ,fig4 #i471 while with wet material the block gives way gradually1 due to the buckling or bending of the walls of the fibres along one or more shearing planes4 7,see ,fig4 #ad47 ,in bending tests on wet beams1 first failure occurs by compression on top of the beam1 gradually extending downward toward the neutral axis4 ,finally the beam ruptures at the bottom4 ,in the case of very dry beams the failure is usually by splitting or tension on the under side 7see ,fig4 #ag471 without compression on the upper1 and is often sudden and without warning1 and even while the load is still increasing4 ,the effect varies somewhat with different species1 chestnut1 for example1 becoming more brittle upon drying than do ash1 hemlock1 and longleaf pine4 ,the tensile strength of wood is least affected by drying1 as a rule4 ,in drying wood no increase in strength results until the free water is evaporated and the cell walls begin to dry#di4 ,this critical point has been called the fibre-saturation point4 7,see ,fig4 #bd47 ,conversely1 after the cell walls are saturated with water1 any increase in the amount of water absorbed merely fills the cavities and intercellular spaces1 and has no effect on the mechanical properties4 ,hence1 soaking green wood does not lessen its strength unless the water is heated1 whereupon a decided weakening results4 ,footnote #di3 ,the wood of ,eucalyptus globulus 7blue gum7 appears to be an exception to this rule4 ,tiemann says3 ,the wood of blue gum begins to shrink immediately from the green condition1 even at #gj to #ij per cent moisture content1 instead of from #cj or #be per cent as in other species of hardwoods4 ,proc4 ,soc4 ,am4 ,for41 ,washington1 ,vol4 ,,viii1 ,no4 #c1 ,oct41 #aiac1 p4 #cac4 ,illustration3 ,,fig4 #bd4--,relation of the moisture content to the various strength values of spruce4 ,,fsp fibre-saturation point4 ,the strengthening effects of drying1 while very marked in the case of small pieces1 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 shrinkage1 and in some cases also to the slitting of the cell walls 7see ,fig4 #be74 ,consequently with large timbers in commercial use it is unsafe to count upon any greater strength1 even after seasoning1 than that of the green or fresh condition4 ,illustration3 ,,fig4 #be4--;,cross section of the wood of western larch showing fissures in the thick-walled cells of the late wood4 ,highly magnified4 ,photo by ,u4 ,s4 ,forest ,service4 ,in green wood the cells are all intimately joined together and are at their natural or normal size when saturated with water4 ,the cell walls may be considered as made up of little particles with water between them4 ,when wood is dried the films of water between the particles become thinner and thinner until almost entirely gone4 ,as a result the cell walls grow thinner with loss of moisture1--in other words1 the cell shrinks4 ,it is at once evident that if drying does not take place uniformly throughout an entire piece of timber1 the shrinkage as a whole cannot be uniform4 ,the process of drying is from the outside inward1 and if the loss of moisture at the surface is met by a steady capillary current of water from the inside1 the shrinkage1 so far as the degree of moisture affected it1 would be uniform4 ,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 begin4 ,in air-seasoning and in ordinary dry kilns this condition too often is not attained1 and the result is that a dry shell is formed which encloses a moist interior4 7,see ,fig4 #bf47 ,subsequent drying out of the inner portion is rendered more difficult by this case-hardened condition4 ,as the outer part dries it is prevented from shrinking by the wet interior1 which is still at its greatest volume4 ,this outer portion must either check open or the fibres become strained in tension4 ,if this outer shell dries while the fibres are thus strained they become set in this condition1 and are no longer in tension4 ,later when the inner part dries1 it tends to shrink away from the hardened outer shell1 so that the inner fibres are now strained in tension and the outer fibres are in compression4 ,if the stress exceeds the cohesion1 numerous cracks open up1 producing a honey-combed condition1 or hollow-horning1 as it is called4 ,if such a case-hardened stick of wood be resawed1 the two halves will cup from the internal tension and external compression1 with the concave surface inward4 ,illustration3 ,,fig4 #bf4--,progress of drying throughout the length of a chestnut beam1 the black spots indicating the presence of free water in the wood4 ,the first section at the left was cut one-fourth inch from the end1 the next one-half inch1 the next one inch1 and all the others one inch apart4 ,the illustration shows case-hardening very clearly4 ,photo by ,u4 ,s4 ,forest ,service4 ,for a given surface area the loss of water from wood is always greater from the ends than from the sides1 due to the fact that the vessels and other water-carriers are cut across1 allowing ready entrance of drying air and outlet for the water vapor4 ,water does not flow out of boards and timbers of its own accord1 but must be evaporated1 though it may be forced out of very sappy specimens by heat4 ,in drying a log or pole with the bark on1 most of the water must be evaporated through the ends1 but in the case of peeled timbers and sawn boards the loss is greatest from the surface because the area exposed is so much greater4 ,the more rapid drying of the ends causes local shrinkage1 and were the material sufficiently plastic the ends would become bluntly tapering4 ,the rigidity of the wood substance prevents this and the fibres are split apart4 ,later1 as the remainder of the stick dries many of the checks will come together1 though some of the largest will remain and even increase in size as the drying proceeds4 7,see ,fig4 #bg47 ,illustration3 ,,fig4 #bg4--;,excessive season checking4 ,photo by ,u4 ,s4 ,forest ,service4 ,a wood cell shrinks very little lengthwise4 ,a dry wood cell is1 therefore1 practically of the same length as it was in a green or saturated condition1 but is smaller in cross section1 has thinner walls1 and a larger cavity4 ,it is at once evident that this fact makes shrinkage more irregular1 for wherever cells cross each other at a decided angle they will tend to pull apart upon drying4 ,this occurs wherever pith rays and wood fibres meet4 ,a considerable portion of every wood is made up of these rays1 which for the most part have their cells lying in a radial direction instead of longitudinally4 7,see ,frontispiece47 ,in pine1 over #ae1jjj of these occur on a square inch of a tangential section1 and even in oak the very large rays which are readily visible to the eye as flakes on quarter-sawed material represent scarcely one per cent of the number which the microscope reveals4 ,a pith ray shrinks in height and width1 that is1 vertically and tangentially as applied to the position in a standing tree1 but very little in length or radially4 ,the other elements of the wood shrink radially and tangentially1 but almost none lengthwise or vertically as applied to the tree4 ,here1 then1 we find the shrinkage of the rays tending to shorten a stick of wood1 while the other cells resist it1 and the tendency of a stick to get smaller in circumference is resisted by the endwise reaction or thrust of the rays4 ,only in a tangential direction1 or around the stick in direction of the annual rings of growth1 do the two forces coincide4 ,another factor to the same end is that the denser bands of late wood are continuous in a tangential direction1 while radially they are separated by alternate zones of less dense early wood4 ,consequently the shrinkage along the rings 7tangential7 is fully twice as much as toward the centre 7radial74 7,see ,table ,,xiv47 ,this explains why some cracks open more and more as drying advances4 7,see ,fig4 #bg47 ,although actual shrinkage in length is small1 nevertheless the tendency of the rays to shorten a stick produces strains which are responsible for some of the splitting open of ties1 posts1 and sawed timbers with box heart4 ,at the very centre of a tree the wood is light and weak1 while farther out it becomes denser and stronger4 ,longitudinal shrinkage is accordingly least at the centre and greater toward the outside1 tending to become greatest in the sapwood4 ,when a round or a box-heart timber dries fast it splits radially1 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 apart4 ,if a small hardwood stem is split while green for a short distance at the end and placed where it can dry out rapidly1 the sections will become bow-shaped with the concave sides out4 ,these various facts1 taken together1 explain why1 for example1 an oak tie1 pole1 or log may split open its entire length if drying proceeds rapidly and far enough4 ,initial stresses in the living trees produce a similar effect when the log is sawn into boards4 ,this is especially so in ,eucalyptus globulus and to a less extent with any rapidly grown wood4 ,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 countries4 ,these devices are driven into the butts of the timbers so as to cross incipient checks and prevent their widening4 ,in place of the regular ,s-hook another of crimped iron has been devised4 7,see ,fig4 #bh47 ,thin straps of iron with one tapered edge are run between intermeshing cogs and crimped1 after which they may be cut off any length desired4 ,the time for driving ,s-irons of either form is when the cracks first appear4 ,illustration3 ,,fig4 #bh4--;,control of season checking by the use of ,s-irons4 ,photo by ,u4 ,s4 ,forest ,service4 ,the tendency of logs to split emphasizes the importance of converting them into planks or timbers while in a green condition4 ,otherwise the presence of large checks may render much lumber worthless which might have been cut out in good condition4 ,the loss would not be so great if logs were perfectly straight-grained1 but this is seldom the case1 most trees growing more or less spirally or irregularly4 ,large pieces crack more than smaller ones1 quartered lumber less than that sawed through and through1 thin pieces1 especially veneers1 less than thicker boards4 ,in order to prevent cracks at the ends of boards1 small straps of wood may be nailed on them or they may be painted4 ,this method is usually considered too expensive1 except in the case of valuable material4 ,squares used for shuttles1 furniture1 gun-stocks1 and tool handles should always be protected at the ends4 ,one of the best means is to dip them into melted paraffine1 which seals the ends and prevents loss of moisture there4 ,another method is to glue paper on the ends4 ,in some cases abroad paper is glued on to all the surfaces of valuable exotic balks4 ,other substances sometimes employed for the purpose of sealing the wood are grease1 carbolineum1 wax1 clay1 petroleum1 linseed oil1 tar1 and soluble glass4 ,in place of solid beams1 built-up material is often preferable1 as the disastrous results of season checks are thereby largely overcome or minimized4 ,,temperature ,the effect of temperature on wood depends very largely upon the moisture content of the wood and the surrounding medium4 ,if absolutely dry wood is heated in absolutely dry air the wood expands4 ,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 specimen4 ,the coefficient of linear expansion of oak has been found to be 4#jjjjjdib2 radial expansion1 4#jjjjedd1 or about eleven times the longitudinal4 ,spruce expands less than oak1 the ratio of radial to longitudinal expansion being about six to one4 ,metals and glass expand equally in all directions1 since they are homogeneous substances1 while wood is a complicated structure4 ,the coefficient of expansion of iron is 4#jjjjbhe1 or nearly six times the coefficient of linear expansion of oak and seven times that of spruce#ej4 ,footnote #ej3 ,see ,schlich's ,manual of ,forestry1 ,vol4 ,v4 7rev4 ed471 p4 #ge4 ,under ordinary conditions wood contains more or less moisture1 so that the application of heat has a drying effect which is accompanied by shrinkage4 ,this shrinkage completely obscures the expansion due to the heating4 ,experiments made at the ,yale ,forest ,school revealed the effect of temperature on the crushing strength of wet wood4 ,in the case of wet chestnut wood the strength decreases #j4db per cent for each degree the water is heated above #fj ,f42 in the case of spruce the decrease is #j4cb per cent4 ,the effects of high temperature on wet wood are very marked4 ,boiling produces a condition of great pliability1 especially in the case of hardwoods4 ,if wood in this condition is bent and allowed to dry1 it rigidly retains the shape of the bend1 though its strength may be somewhat reduced4 ,except in the case of very dry wood the effect of cold is to increase the strength and stiffness of wood4 ,the freezing of any free water in the pores of the wood will augment these conditions4 ,the effect of steaming upon the strength of cross-ties was investigated by the ,u4,s4 ,forest ,service in #aijd4 ,the conclusions were summarized as follows3 7#a7 ,the steam at pressure up to #dj pounds applied for #d hours1 or at a pressure of #bj pounds up to #bj hours1 increases the weight of ties4 ,at #dj pounds' pressure applied for #d hours and at #bj pounds for #e hours the wood began to be scorched4 7#b7 ,the steamed and saturated wood1 when tested immediately after treatment1 exhibited weaknesses in proportion to the pressure and duration of steaming4 7,see ,table ,,xvi47 ,if allowed to air-dry subsequently the specimens regained the greater part of their strength1 provided the pressure and duration had not exceeded those cited under 7#a74 ,subsequent immersion in water of the steamed wood and dried specimens showed that they were weaker than natural wood similarly dried and resoaked4#ea ,footnote #ea3 ,cir4 #ci4 ,experiments on the strength of treated timber1 p4 #ah4 ---------------------------------------- ---------------------------------------- ---------- ,,table ,,xvi ---------------------------------------- ---------------------------------------- ---------- ,,effect ,,of ,,steaming ,,on ,,the ,,strength ,,of ,,green ,,loblolly ,,pine 7,forest ,service1 ,cir4 #ci7 ---------------------------------------- ---------------------------------------- ---------- ,cylinder conditions ,strength ---------------------------------------- ------------------------------------- ,steaming ,static ,impact ---------------------------------------- ------------------------ ,average ,treatment ,bending ,compres- ,height of the modulus sion of drop three ,period ,pressure ,temperature of parallel causing strengths rupture to grain complete failure ---------------------------------------- ---------------------------------------- --- ,lbs4 per ,per cent ,per cent ,per cent ,per cent ,hrs4 sq4 inch ,f4 ,untreated wood #ajj ,steam1 #d #bcj;a #ia4c #gi4a #if4d #hh4i at #d #aj #bch #gh4b #ic4g #ic4c #hh4d various #d #bj #bec #hc4c #hd4b #ia4d #hj4h pressures #d #cj #bfi #hj4d #gh4d #hi4h #hb4i #d #dj #bhc #gh4a #gd4d #gd4j #ge4e #d #ej #bib #ge4h #ga4e #fc4i #gj4d #d #ajj #ccg #da4d #fe4j #ee4b #ec4i ---------------------------------------- ---------------------------------------- --- ,steam1 #a #bj #beg #ajj4f #ih4f #hf4g #ie4c for #b #bj #bfg #hh4d #ic4j #ajg4j #if4a various #c #bj #bfj #ij4j #ic4f #hd4a #hi4b periods #d #bj #bec #hc4c #hd4b #ia4d #hf4c #e #bj #bec #he4j #gh4a #hd4b #hb4d #f #bj #bdb #ie4b #hi4h #gf4j #hg4j #aj #bj #bee #gc4g #hb4j #gf4j #gg4b #bj #bj #beh #fg4e #fe4j #ii4j #gg4b ---------------------------------------- ---------------------------------------- ---------- ,footnote a3 ,it will be noted that the temperature was #bcj4 ,this is the maximum temperature by the maximum-temperature recording thermometer1 and is due to the handling of the exhaust valve4 ,the average temperature was that of exhaust steam4 ---------------------------------------- ---------------------------------------- ---------- 7#c7 ,a high degree of steaming is injurious to wood in strength and spike-holding power4 ,the degree of steaming at which pronounced harm results will depend upon the quality of the wood and its degree of seasoning1 and upon the pressure 7temperature7 of steam and the duration of its application4 ,for loblolly pine the limit of safety is certainly #cj pounds for #d hours1 or #bj pounds for #f hours4#eb ,footnote #eb3 ,ibid41 p4 #ba4 ,see also ,cir4 #ajh1 p4 #ai1 table #e4 ,experiments made at the ,yale ,forest ,school showed that steaming above #cj pounds' gauge pressure reduces the strength of wood permanently while wet from #be to #ge per cent4 ,,preservatives ,the exact effects of chemical impregnation upon the mechanical properties of wood have not been fully determined1 though they have been the subject of considerable investigation4#ec ,more depends upon the method of treatment than upon the preservatives used4 ,thus preliminary steaming at too high pressure or for too long a period will materially weaken the wood1 7,see ,,temperature1 above47 ,footnote #ec3 ,hatt1 ,w4 ,k43 ,experiments on the strength of treated timber4 ,cir4 #ci1 ,u4,s4 ,forest ,service1 #aijf1 p4 #ca4 ,the presence of zinc chloride does not weaken wood under static loading1 although the indications are that the wood becomes brittle under impact4 ,if the solution is too strong it will decompose the wood4 ,soaking in creosote oil causes wood to swell1 and accordingly decreases the strength to some extent1 but not nearly so much so as soaking in water4#ed ,footnote #ed3 ,teesdale1 ,clyde ,,ii43 ,the absorption of creosote by the cell walls of wood4 ,cir4 #bjj1 ,u4 ,s4 ,forest ,service1 #aiab1 p4 #g4 ,soaking in kerosene seems to have no significant weakening effect4#ee ,footnote #ee3 ,tiemann1 ,h4,d43 ,effect of moisture upon the strength and stiffness of wood4 ,bul4 #gj1 ,u4 ,s4 ,forest ,service1 #aijg1 pp4 #abb-abc1 tables #dc-dd4 ,,part ,,iii ,,timber ,,testing#ef ,footnote #ef3 ,the methods of timber testing described here are for the most part those employed by the ,u4 ,s4 ,forest ,service4 ,see ,cir4 #ch 7rev4 ed471 #aiji4 ,,working ,,plan ,preliminary to making a series of timber tests it is very important that a working plan be prepared as a guide to the investigation4 ,this should embrace3 7#a7 the purpose of the tests2 7#b7 kind1 size1 condition1 and amount of material needed2 7#c7 full description of the system of marking the pieces2 7#d7 details of any special apparatus and methods employed2 7#e7 proposed method of analyzing the data obtained and the nature of the final report4 ,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 avoided4 ,a comprehensive study of previous investigations along the same or related lines should prove very helpful in outlining the work and preparing the report4 7,for sample working plan see ,appendix47 ,,forms ,,of ,,material ,,tested ,in general1 four forms of material are tested1 namely3 7#a7 large timbers1 such as bridge stringers1 car sills1 large beams1 and other pieces five feet or more in length1 of actual sizes and grades in common use2 7#b7 built-up structural forms and fastenings1 such as built-up beams1 trusses1 and various kind of joints2 7#c7 small clear pieces1 such as are used in compression1 shear1 cleavage1 and small cross-breaking tests2 7#d7 manufactured articles1 such as axles1 spokes1 shafts1 wagon-tongues1 cross-arms1 insulator pins1 barrels1 and packing boxes4 ,as the moisture content is of fundamental importance 7see ,,water ,,content1 above471 all standard tests are usually made in the green condition4 ,another series is also usually run in an air-dry condition of about #ab per cent moisture4 ,in all cases the moisture is very carefully determined and stated with the results in the tables4 ,,size ,,of ,,test ,,specimens ,the size of the test specimen must be governed largely by the purpose for which the test is made4 ,if the effect of a single factor1 such as moisture1 is the object of experiment1 it is necessary to use small pieces of wood in order to eliminate so far as possible all disturbing factors4 ,if the specimens are too large1 it is impossible to secure enough perfect pieces from one tree to form a series for various tests4 ,moreover1 the drying process with large timbers is very difficult and irregular1 and requires a long period of time1 besides causing checks and internal stresses which may obscure the results obtained4 ,on the other hand1 the smaller the dimensions of the test specimen the greater becomes the relative effect of the inherent factors affecting the mechanical properties4 ,for example1 the effect of a knot of given size is more serious in a small stick than in a large one4 ,moreover1 the smaller the specimen the fewer growth rings it contains1 hence there is greater opportunity for variation due to irregularities of grain4 ,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 market2 their coefficients of elasticity under bending 7since the stiffness rather than the strength often determines the size of a beam72 and the manner of failure1 whether in bending fibre stress or horizontal shear4 ,it is believed that this information can only be obtained by direct tests on the different grades of car sills1 stringers1 and other material in common use4 ,when small pieces are selected for test they very often are clear and straight-grained1 and thus of so much better grade than the large sticks that tests upon them may not yield unit values applicable to the larger sizes4 ,extensive experiments show1 however1 7#a7 that the modulus of elasticity is approximately the same for large timbers as for small clear specimens cut from them1 and 7#b7 that the fibre stress at elastic limit for large beams is1 except in the weakest timbers1 practically equal to the crushing strength of small clear pieces of the same material4#eg ,footnote #eg3 ,bul4 #ajh1 ,u4 ,s4 ,forest ,service3 ,tests of structural timbers1 pp4 #ec-ed4 ,,moisture ,,determination ,in order for tests to be comparable1 it is necessary to know the moisture content of the specimens at the zone of failure4 ,this is determined from disks an inch thick cut from the timber immediately after testing4 ,in cases1 as in large beams1 where it is desirable to know not only the average moisture content but also its distribution through the timber1 the disks are cut up so as to obtain an outside1 a middle1 and an inner portion1 of approximately equal areas4 ,thus in a section #aj x #ab the outer strip would be one inch wide1 and the second one a little more than an inch and a quarter4 ,moisture determinations are made for each of the three portions separately4 ,the procedure is as follows3 7#a7 ,immediately after sawing1 loose splinters are removed and each section is weighed4 7#b7 ,the material is put into a drying oven at #ajj ,c4 7#bab ,f47 and dried until the variation in weight for a period of twenty-four hours is less than #j4e per cent4 7#c7 ,the disk is again carefully weighed4 7#d7 ,the loss in weight expressed in per cent of the dry weight indicates the moisture content of the specimen from which the specimen was cut4 ,,machine ,,for ,,static ,,tests ,the standard screw machines used for metal tests are also used for wood1 but in the case of wood tests the readings must be taken on the fly1 and the machine operated at a uniform speed without interruption from beginning to end of the test4 ,this is on account of the time factor in the strength of wood4 7,see ,,speed ,,of ,,testing ,,machine1 below47 ,the standard machines for static tests can be used for transverse bending1 compression1 tension1 shear1 and cleavage4 ,a common form consists of three main parts1 namely3 7#a7 the straining mechanism1 7#b7 the weighing apparatus1 and 7#c7 the machinery for communicating motion to the screws4 ,the straining mechanism consists of two parts1 one of which is a movable crosshead operated by four 7sometimes two or three7 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 fulcrum4 ,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 desired4 ,the stationary part of the straining mechanism1 which is used only for tension and cleavage tests1 consists of a steel cage above the movable crosshead and rests directly upon the weighing platform4 ,the top of the cage contains a square hole into which one end of the test specimen may be clamped1 the crosshead containing a similar clamp for the other end1 in making tension tests4 ,for testing long beams a special form of machine with an extended platform is used4 7,see ,fig4 #bi47 ,the weighing platform rests upon knife edges carried by primary levers of the weighing apparatus1 the fulcrum being on the bed of the machine1 and any pressure upon it is directly transmitted through a series of levers to the weighing beam4 ,this beam is adjusted by means of a poise running on a screw4 ,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 automatically4 ,the larger units of stress are read from the graduations along the side of the beam1 while the intermediate smaller weights are observed on the dial on the rear end of the beam4 ,the machine is driven by power from a shaft or a motor and is so geared that various speeds are obtainable4 ,one man can operate it4 ,in making tests the operation of the straining screws is always downward so as to bring pressure to bear upon the weighing platform4 ,for tests in tension and cleavage the specimen is placed between the top of the stationary cage and the movable head and subjected to a pull4 ,for tests in transverse bending1 compression1 and cleavage the specimen is placed between the movable head and the platform1 and a direct compression force applied4 ,testing machines are usually calibrated to a portion of their capacity before leaving the factory4 ,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 #a1jjj pounds rests on the platform4 ,the usual requirement is that ten pounds should accomplish this movement4 ,the size of machine suitable for compression tests on #b ,x #b sticks or for #b ,x #b beams with #bf to #cf-;inch span has a capacity of #cj1jjj pounds4 ,,speed ,,of ,,testing ,,machine ,in instructions for making static tests the rate of application of the stress1 i4e41 the speed of the machine1 is given because the strength of wood varies with the speed at which the fibres are strained4 ,the speed of the crosshead of the testing machine is practically never constant1 due to mechanical defects of the apparatus and variations in the speed of the motor1 but so long as it does not exceed #be per cent the results will not be appreciably affected4 ,in fact1 a change in speed of #ej per cent will not cause the strength of the wood to vary more than #b per cent4#eh ,footnote #eh3 ,see ,tiemann1 ,harry ,donald3 ,the effect of the speed of testing upon the strength and the standardization of tests for speed4 ,proc4 ,am4 ,soc4 for ,testing ,materials1 ,vol4 ,,viii1 ,philadelphia1 #aijh4 ,following are the formul used in determining the speed of the movable head of the machine in inches per minute 7n73 7#a7 ,for endwise compression n ,z l ,z l#b 7#b7 ,for beams 7centre loading7 n --------- #f;h ,z l#b 7#c7 ,for beams 7third-pointloading7 n --------- #e4d;h ,z rate of fibre strain per inch of fibre length4 l span of beam or length of compression specimen4 h height of beam4 ,the values commonly used for ,z are as follows3 ,bending large beams ,z #j4jjjg ,bending small beams ,z #j4jjae ,endwise compression-large specimens ,z #j4jjae ,endwise compression-small ,z #j4jjc ,right-angled compression-large ,z #j4jjg ,right-angled compression-small ,z #j4jae ,shearing parallel to the grain ,z #j4jae ,example3 ,at what speed should the crosshead move to give the required rate of fibre strain in testing a small beam #b ,x #b ,x #cj4 7,span #bh47 ,substituting these values in equation 7#b7 above3 7#j4jjae ,x #bhb7 n ----------------- #j4a inch per minute4 7#f ,x #b7 ,in order that tests may be intelligently compared1 it is important that account be taken of the speed at which the stress was applied4 ,in determining the basis for a ratio between time and strength the rate of strain1 which is controllable1 and not the ratio of stress1 which is circumstantial1 should be used4 ,in other words1 the rate at which the movable head of the testing machine descends and not the rate of increase in the load is to be regulated4 ,this ratio1 to which the name speed-strength modulus has been given1 may be expressed as a coefficient which1 if multiplied into any proportional change in speed1 will give the proportional change in strength4 ,this ratio is derived from empirical curves4 7,see ,table ,,xvii47 ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- --------------------------------- ,,table ,,xvii ,,table ,,xvii ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- --------------------------------- ,,speed-,,strength ,,moduli ,,and ,,relative ,,increase ,,in ,,strength ,,at ,,rates ,,of ,,fibre ,,strain ,,increasing ,,in ,,geometrical ,,ratio4 7,tiemann1 loc4 cit47 7,values in parentheses are approximate7 ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- --------------------------------- ,rate of fibre strain4 ,ten-thousandths inch #b_/c #b #f #ah #ed #afb #dhf per minute per inch ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- -------------------------- ,c ,speed of crosshead4 ,o ,inches per minute #j4jjjchc #j4jjaae #j4jjcde #j4jajc #j4jcaj #j4jica 4#bgi ,m ,p ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------- ,r ,specimens ,wet ,dry ,all ,wet ,dry ,all ,wet ,dry ,all ,wet ,dry ,all ,wet ,dry ,all ,wet ,dry ,all ,wet ,dry ,all ,e ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- -------- ,s ,relative ,s crushing #ajj4j #ajj4j #ajj4j #ajc4d #ajj4h #aja4e #ajg4e #ajb4g #ajc4h #aac4i #aje4e #ajg4i #aba4c #ajh4c #aaf4d #abh4h #aaj4j #aah4i ,i strength ,o ,n ,speed-strength #j4jag 7#j4jjf77j4jji7 #j4jcc #j4jab #j4jaf #j4jdg #j4jba #j4jbi #j4jec #j4jbg #j4jci #j4jfj #j4jbc #j4jdi 7#j4jeb77j4jae77j4jdj7 modulus1 ,t ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ------------------------- ,speed of crosshead4 ,inches per minute #j4jjgb #j4jbaf #j4jfdh #j4aid #j4ehc #a4ge #e4be ,b ,e ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------- ,n ,specimens ,wet ,dry ,all ,wet ,dry ,all ,wet ,dry ,all ,wet ,dry ,all ,wet ,dry ,all ,wet ,dry ,all ,wet ,dry ,all ,d ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- -------- ,i ,relative ,n crushing #ig4d #ii4j #ih4b #ajj4j #ajj4j #ajj4j #aje4a #ajb4a #ajc4g #aaa4c #aje4h #ajh4a #aag4i #ajh4f #aab4g #abc4g #aji4f #aaf4c #abf4c #aaj4c #aah4i ,g strength ,speed-strength 7#j4jad77j4jje7 #j4jab #j4jcc #j4jad #j4jbf #j4jdi #j4jbf #j4jcg #j4jec #j4jcc #j4jch #j4jdi #j4jad #j4jce #j4jch #j4jjf #j4jbe 7#j4jbc77j4jjd77j4jad7 modulus1 ,t ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- --------------------------------- ,,note4--,the usual speeds of testing at the ,u4,s4 ,forest ,service laboratory are at rates of fibre strain of #ae and #aj ten-thousandths in4 per min4 per in4 for compression and bending respectively4 ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- --------------------------------- ,,bending ,,large ,,beams ,apparatus3 ,a static bending machine 7described above71 with a special crosshead for third-point loading and a long platform bearing knife-edge supports1 is required4 7,see ,fig4 #bi47 ,illustration3 ,,fig4 #bi4--,static bending test on large beam4 ,note arrangement of wire and scale for measuring deflection2 also method of applying load at third-points4 ,preparing the material3 ,standard sizes and grades of beams and timbers in common use are employed4 ,the ends are roughly squared and the specimen weighed and measured1 taking the cross-sectional dimensions midway of the length4 ,weights should be to the nearest pound1 lengths to the nearest #j4a inch1 and cross-sectional dimensions to the nearest #j4ja inch4 ,marking and sketching3 ,the butt end of the beam is marked ,a and the top end ,b4 ,while facing ,a1 the top side is marked a1 the right hand b1 the bottom c1 the left hand d4 ,sketches are made of each side and end1 showing 7#a7 size1 location1 and condition of knots1 checks1 splits1 and other defects2 7#b7 irregularities of grain2 7#c7 distribution of heartwood and sapwood2 and on the ends3 7#d7 the location of the pith and the arrangement of the growth rings1 7#e7 number of rings per inch1 and 7#f7 the proportion of late wood4 ,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 rings4 ,the average number of rings per inch is the total number of rings divided by the length of the line crossing them4 ,the proportion of late wood is equal to the sum of the widths of the late wood crossed by the line1 divided by the length of the line4 ,rings per inch should be to the nearest #j4a2 late wood to the nearest #j4a per cent4 ,since in large beams a great variation in rate of growth and relative amount of late wood is likely in different parts of the section1 it is advisable to consider the cross section in three volumes1 namely1 the upper and lower quarters and the middle half4 ,the determination should be made upon each volume separately1 and the average for the entire cross section obtained from these results4 ,at the conclusion of the test the failure1 as it appears on each surface1 is traced on the sketches1 with the failures numbered in the order of their occurrence4 ,if the beam is subsequently cut up and used for other tests an additional sketch may be desirable to show the location of each piece4 ,adjusting specimen in machine3 ,the beam is placed in the machine with the side marked a on top1 and with the ends projecting equally beyond the supports4 ,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 beam4 ,roller bearings should be placed between the bearing blocks and the knife edges of the crosshead to allow for the shortening due to flexure4 7,see ,fig4 #bi47 ,third-point loading is used1 that is1 the load is applied at two points one-third the span of the beam apart4 7,see ,fig4 #cj47 ,this affords a uniform bending moment throughout the central third of the beam4 ,illustration3 ,,fig4 #cj4--,two methods of loading a beam1 namely1 third-point loading 7upper71 and centre loading 7lower74 ,measuring the deflection3 ,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 reading4 ,this may be accomplished by driving a small nail near each end of the beam1 the exact location being on the neutral plane and vertically above each knife-edge support4 ,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 end4 ,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 it4 ,attachment should be made on the neutral plane4 ,the first reading is made when the scale beam is balanced at zero load1 and afterward at regular increments of the load which is applied continuously and at a uniform speed4 7,see ,,speed ,,of ,,testing ,,machine1 above47 ,if desired1 however1 the load may be read at regular increments of deflection4 ,the deflection readings should be to the nearest #j4ja inch4 ,to avoid error due to parallax1 the readings may be taken by means of a reading telescope about ten feet distant and approximately on a level with the wire4 ,a mirror fastened to the scale will increase the accuracy of the readings if the telescope is not used4 ,as in all tests on timber1 the strain must be continuous to rupture1 not intermittent1 and readings must be taken on the fly4 ,the weighing beam is kept balanced after the yield point is reached and the maximum load1 and at least one point beyond it1 noted4 ,log of the test3 ,the proper log sheet for this test consists of a piece of cross-section paper with space at the margin for notes4 7,see ,fig4 #cb47 ,the load in some convenient unit 7#a1jjj to #aj1jjj pounds1 depending upon the dimensions of the specimen7 is entered on the ordinates1 the deflection in tenths of an inch on the absciss4 ,the increments of load should be chosen so as to furnish about ten points on the stress-strain diagram below the elastic limit4 ,as the readings of the wire on the scale are made they are entered directly in their proper place on the cross-section paper4 ,in many cases a test should be continued until complete failure results4 ,the points where the various failures occur are indicated on the stress-strain diagram4 ,a brief description of the failure is made on the margin of the log sheet1 and the form traced on the sketches4 ,disposal of the specimen3 ,two one-inch sections are cut from the region of failure to be used in determining the moisture content4 7,see ,,moisture ,,determination1 above47 ,a two-inch section may be cut for subsequent reference and identification1 and possible microscopic study4 ,the remainder of the beam may be cut into small beams and compression pieces4 ,calculating the results3 ,the formul used in calculating the results of tests on large rectangular simple beams loaded at third points of the span are as follows3 #j4ge ,p 7#a7 ,j -------- b h l 7,p#a #j4ge ,w7 7#b7 r -------------------- b h#b l 7,p #j4ge ,w7 7#c7 ,r ---------------- b h#b ,p#a l#c 7#d7 ,e --------------- #d4g ,d b h#c #j4hg ,p#a ,d 7#e7 ,s -------------- #b ,v b1 h1 l breadth1 height1 and span of specimen1 inches4 ,d total deflection at elastic limit1 inches4 ,p maximum load1 pounds4 ,p#a load at elastic limit1 pounds4 ,e modulus of elasticity1 pounds per square inch4 r fibre stress at elastic limit1 pounds per sq4 inch4 ,r modulus of rupture1 pounds per square inch4 ,s elastic resilience or work to elastic limit1 inch-pounds per cu4 in4 ,j greatest calculated longitudinal shear1 pounds per square inch4 ,v volume of beam1 cubic inches4 ,w weight of the beam4 ,in large beams the weight should be taken into account in calculating the fibre stress4 ,in 7#b7 and 7#c7 three-fourths of the weight of the beam is added to the load for this reason4 ,,bending ,,small ,,beams ,apparatus3 ,an ordinary static bending machine1 a steel ,i-beam bearing two adjustable knife-edge supports to rest on the platform1 and a special deflectometer1 are required4 7,see ,fig4 #ca47 ,illustration3 ,,fig4 #ca4--,static bending test on small beam4 ,note the use of the deflectometer with indicator and dial for measuring the deflection2 also roller bearings between beam and supports4 ,preparing the material3 ,the specimens may be of any convenient size1 though beams #b ,x #b ,x #cj tested over a #bh-;inch span1 are considered best4 ,the beams are surfaced on all four sides1 care being taken that they are not damaged by the rollers of the surfacing machine4 ,material for these tests is sometimes cut from large beams after failure4 ,the specimens are carefully weighed in grams1 and all dimensions measured to the nearest #j4ja inch4 ,if to be tested in a green or fresh condition the specimens should be kept in a damp box or covered with moist sawdust until needed4 ,no defects should be allowed in these specimens4 ,marking and sketching3 ,sketches are made of each end of the specimen to show the character of the growth1 and after testing1 the manner of failure is shown for all four sides4 ,in obtaining data regarding the rate of growth and the proportion of late wood the same procedure is followed as with large beams4 ,adjusting specimen in machine3 ,the beam should be correctly centred in the machine and each end should have a plate with roller bearings between it and the support4 ,centre loading is used4 ,between the movable head of the machine and the specimen is placed a bearing block of maple or other hard wood1 the lower surface of which is curved in a direction along the beam1 the curvature of which should be slightly less than that of the beam at rupture1 in order to prevent the edges from crushing into the fibres of the test piece4 ,measuring the deflection3 ,the method of measuring deflection of large beams can be used for small sizes1 but because of the shortness of the span and consequent slight deformation in the latter1 it is hardly accurate enough for good work4 ,the special deflectometer shown in ,fig4 #ca allows closer reading1 as it magnifies the deflection ten times4 ,it rests on two small nails driven in the beam on the neutral plane and vertically above the supports4 ,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 nails4 ,all three nails should be in place before the beam is put into the machine4 ,the indicator is adjustable by means of a thumb-screw at the base and is set at zero before the load is applied4 ,deflections are read to the nearest #j4jja inch4 ,for rate of application of load see ,,speed ,,of ,,testing ,,machine1 above4 ,the speed should be uniform from start to finish without stopping4 ,readings must be made on the fly4 ,log of the test3 ,the log sheets used for small beams 7see ,fig4 #cb7 are the same as for large sizes and the procedure is practically identical4 ,the stress-strain diagram is continued to or beyond the maximum load1 and in a portion of the tests should be continued to six-inch deflection or until the specimen fails to support a load of #bjj pounds4 ,deflection readings for equal increments of load are taken until well beyond the elastic limit1 after which the scale beam is kept balanced and the load read for each #j4a inch deflection4 ,the load and deflection at first failure1 the maximum load1 and any points of sudden change should be shown on the diagram1 even though they do not occur at one of the regular points4 ,a brief description of the failure and the nature of any defects is entered on the log sheet4 ,illustration3 ,,fig4 #cb4--,sample log sheet1 giving full details of a transverse bending test on a small pine beam4 ,calculating the results3 ,the formul used in calculating the results of tests on small rectangular simple beams are as follows3 #j4ge ,p 7#a7 ,j -------- b h #a4e ,p#a l 7#b7 r ------------- b h#b #a4e ,p l 7#c7 ,r --------- b h#b ,p#a l#c 7#d7 ,e ------------- #d ,d b h#c ,p#a ,d 7#e7 ,s --------- #b ,v ,the same legend is used as in ,,bending ,,large ,,beams4 ,the weight of the beam itself is disregarded4 ,,endwise ,,compression ,apparatus3 ,an ordinary static testing machine and a compressometer are required4 7,see ,fig4 #cc47 ,illustration3 ,,fig4 #cc4--;,endwise compression test1 showing method of measuring the deformation by means of a compressometer4 ,preparing the material3 ,two classes of specimens are commonly used1 namely1 7#a7 posts #bd inches in length1 and 7#b7 small clear blocks approximately #b ,x #b ,x #h4 ,the specimens are surfaced on all four sides and both ends squared smoothly and evenly4 ,they are carefully weighed1 measured1 rate of growth and proportion of late wood determined1 as in bending tests4 ,after the test a moisture section is cut and weighed4 ,ordinarily these specimens should be free from defects4 ,sketching3 ,sketches are made of each end of the specimens to show the character of the growth4 ,after testing1 the manner of failure is shown for all four sides1 and the various parts of the failure are numbered in the order of their occurrence4 ,adjusting specimen in machine3 ,the compressometer collars are adjusted1 the distance between them being #bj inches for the posts and #f inches for the blocks4 ,if the two ends of the blocks are not exactly parallel a ball-and-socket block can be placed between the upper end of the specimen and the movable head of the machine to overcome the irregularity4 ,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 end4 ,measuring the deformation3 ,the deformation is measured by a compressometer4 7,see ,fig4 #cc47 ,the latter registers to #j4jja inch4 ,in the case of posts the compression between the collars is communicated to the four points on the arms by means of brass rods2 with short blocks1 as in ,fig4 #cc1 the points of the arms are in direct contact with the collars4 ,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 it1 being guided by a bell operated by electric contact4 ,log of the test3 ,the load is applied continuously at a uniform rate of speed4 7,see ,,speed ,,of ,,testing ,,machine1 above47 ,readings are taken from the scale of the compressometer at regular increments of either load or compression4 ,the stress-strain diagram is continued to at least one deformation point beyond the maximum load1 and in event of sudden failure1 the direction of the curve beyond the maximum point is indicated4 ,a brief description of the failure is entered on the log sheet4 7,see ,fig4 #cd47 ,illustration3 ,,fig4 #cd4--,sample log sheet of an endwise compression test on a short pine column4 ,in short specimens the failure usually occurs in one or several planes diagonal to the axis of the specimen4 ,if the ends are more moist than the middle a crushing may occur on the extreme ends in a horizontal plane4 ,such a test is not valid and should always be culled4 ,if the grain is diagonal or the stress is unevenly applied a diagonal shear may occur from top to bottom of the test specimen4 ,such tests are also invalid and should be culled4 ,when the plane 7or several planes7 of failure occurs through the body of the specimen the test is valid4 ,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 body4 ,this is a perfectly legitimate procedure provided no drying is allowed from the sides of the specimen1 and the moisture disk is cut from the region of failure4 ,calculating the results3 ,the formul used in calculating the results of tests on endwise compression are as follows3 ,p 7#a7 ,c ----- ,a ,p#a 7#b7 c ------- ,a ,p#a l 7#c7 ,e --------- ,a ,d ,p ,d 7#d7 ,s ----- #b ,v ,c crushing strength1 pounds per square inch4 c fibre strength at elastic limit1 pounds per square inch4 ,a area of cross section1 square inches4 l distance between centres of collars1 inches4 ,d total shortening at elastic limit1 inches4 ,v volume of specimen1 cubic inches4 ,remainder of legend as in ,,bending ,,large ,,beams1 above4 ,,compression ,,across ,,the ,,grain ,apparatus3 ,an ordinary static testing machine1 a bearing plate1 and a deflectometer are required4 7,see ,fig4 #ce47 ,illustration3 ,,fig4 #ce4--;,compression across the grain4 ,note method of measuring the deformation by means of a deflectomoter4 ,preparing the material3 ,two classes of specimens are used1 namely1 7#a7 sections of commercial sizes of ties1 beams1 and other timbers1 and 7#b7 small1 clear specimens with the length several times the width4 ,sometimes small cubes are tested1 but the results are hardly applicable to conditions in practice4 ,in 7#b7 the sides are surfaced and the ends squared4 ,the specimens are then carefully measured and weighed1 defects noted1 rate of growth and proportion of late wood determined1 as in bending tests4 7,see ,,bending ,,large ,,beams1 above47 ,after the test a moisture section is cut and weighed4 ,sketching3 ,sketches are made as in endwise compression tests4 7,see ,,endwise ,,compression1 above47 ,adjusting specimen in machine3 ,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 head4 ,for the larger specimens this plate is six inches wide2 for the smaller sizes1 two inches wide4 ,the plate in all cases projects over the edges of the test piece1 and in no case should the length of the latter be less than four times the width of the plate4 ,measuring the deformation3 ,the compression is measured by means of a deflectometer 7see ,fig4 #ce71 which1 after the first increment of load is applied1 is adjusted 7by means of a small set screw7 to read zero4 ,the actual downward motion of the movable head 7corresponding to the compression of the specimen7 is multiplied ten times on the scale from which the readings are made4 ,log of the test3 ,the load is applied continuously and at uniform speed 7see ,,speed ,,of ,,testing ,,machine1 above71 until well beyond the elastic limit4 ,the compression readings are taken at regular load increments and entered on the cross-section paper in the usual way4 ,usually there is no real maximum load in this case1 as the strength continually increases as the fibres are crushed more compactly together4 ,calculating the results3 ,ordinarily only the fibre stress at the elastic limit 7c7 is computed4 ,it is equal to the load at elastic limit 7,p#a7 divided by the area under the plate 7,b74 ,p#a c ------- ,b ,,shear ,,along ,,the ,,grain ,apparatus3 ,an ordinary static testing machine and a special tool designed for producing single shear are required4 7,see ,figs4 #cf and #cg47 ,this shearing apparatus consists of a solid steel frame with set screws for clamping the block within it firmly in a vertical position4 ,in the centre of the frame is a vertical slot in which a square-edged steel plate slides freely4 ,when the testing block is in position1 this plate impinges squarely along the upper surface of the tenon or lip1 which1 as vertical pressure is applied1 shears off4 ,illustration3 ,fig4 #cf4--,vertical section of shearing tool4 ,illustration3 ,,fig4 #cg4--;,front view of shearing tool with test specimen and steel plate in position for testing4 ,preparing the material3 ,the specimens are usually in the form of small1 clear1 straight-grained blocks with a projecting tenon or lip to be sheared off4 ,two common forms and sizes are shown in ,figure #ch4 ,part of the blocks are cut so that the shearing surface is parallel to the growth rings1 or tangential2 others at right angles to the growth rings1 or radial4 ,it is important that the upper surface of the tenon or lip be sawed exactly parallel to the base of the block4 ,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 below4 ,illustration3 ,,fig4 #ch4--,two forms of shear test specimens4 ,in designing a shearing specimen it is necessary to take into consideration the proportions of the area of shear1 since1 if the length of the portion to be sheared off is too great in the direction of the shearing face1 failure would occur by compression before the piece would shear4 ,inasmuch as the endwise compressive strength is sometimes not more than five times the shearing strength1 the shearing surface should be less than five times the surface to which the load is applied4 ,this condition is fulfilled in the specimens illustrated4 ,shearing specimens are frequently cut from beams after testing4 ,in this case the specific gravity 7dry71 proportion of late wood1 and rate of growth are assumed to be the same as already recorded for the beams4 ,in specimens not so taken1 these quantities are determined in the usual way4 ,the sheared-off portion is used for a moisture section4 ,adjusting specimen in machine3 ,the test specimen is placed in the shearing apparatus with the tenon or lip under the sliding plate1 which is centred under the movable head of the machine4 7,see ,fig4 #ci47 ,in order to reduce to a minimum the friction due to the lateral pressure of the plate against the bearings of the slot1 the apparatus is sometimes placed upon several parallel steel rods to form a roller base4 ,a slight initial load is applied to take up the lost motion of the machinery1 and the beam balanced4 ,illustration3 ,,fig4 #ci4--,making a shearing test4 ,log of the test3 ,the load is applied continuously and at a uniform rate until failure1 but no deformations are measured4 ,the points noted are the maximum load and the length of time required to reach it4 ,sketches are made of the failure4 ,if the failure is not pure shear the test is culled4 ,the shearing strength per square inch is found by dividing the ,p maximum load by the cross-sectional area4 ,q --- ,a ,,impact ,,test ,apparatus3 ,there are several types of impact testing machines4#ei ,one of the simplest and most efficient for use with wood is illustrated in ,figure #dj4 ,the base of the machine is #g feet long1 #b4e feet wide at the centre1 and weighs #c1ejj pounds4 ,two upright columns1 each #h feet long1 act as guides for the striking head4 ,at the top of the column is the hoisting mechanism for raising or lowering the striking weights4 ,the power for operating the machine is furnished by a motor set on the top4 ,the hoisting-mechanism is all controlled by a single operating lever1 shown on the side of the column1 whereby the striking weight may be raised1 lowered1 or stopped at the will of the operator4 ,there is an automatic safety device for stopping the machine when the weight reaches the top4 ,footnote #ei3 ,for description of ,u4,s4 ,forest ,service automatic and autographic impact testing machine1 see ,proc4 ,am4 ,soc4 for ,testing ,materials1 ,vol4 ,,viii1 #aijh1 pp4 #ech-edj4 ,illustration3 ,,fig4 #dj4--;,impact testing machine4 ,the weight is lifted by a chain1 one end of which passes over a sprocket wheel in the hoisting mechanism4 ,on the lower end of the chain is hung an electro-magnet of sufficient magnetic strength to support the heaviest striking weights4 ,when it is desired to drop the striking weight the electric current is broken and reversed by means of an automatic switch and current breaker4 ,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 current4 ,there are four striking weights1 weighing respectively #ej1 #ajj1 #bej1 and #ejj pounds1 any one of which may be used1 depending upon the desired energy of blow4 ,when used for compression tests a flat steel head six inches in diameter is screwed into the lower end of the weight4 ,for transverse tests1 a well-rounded knife edge is screwed into the weight in place of the flat head4 ,knife edges for supporting the ends of the specimen to be tested1 are securely bolted to the base of the machine4 ,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 head4 7,see ,fig4 #da47 ,when a drop is made the pencil comes in contact with the drum and is held in place by a spring4 ,the drum is revolved very slowly1 either automatically or by hand4 ,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 second4 ,illustration3 ,,fig4 #da4--;,drum record of impact bending test4 ,one size of this machine will handle specimens for transverse tests #i inches wide and #f-;foot span2 the other1 #ab inches wide and #h-;foot span4 ,for compression tests a free fall of about #f4e feet may be obtained4 ,for transverse tests the fall is a little less1 depending upon the size of the specimen4 ,the machine is calibrated by dropping the hammer upon a copper cylinder4 ,the axial compression of the plug is noted4 ,the energy used in static tests to produce this axial compression under stress in a like piece of metal is determined4 ,the external energy of the blow 7i4e41 the weight of the hammer ,x the height of drop7 is compared with the energy used in static tests at equal amounts of compression4 ,for instance3 ,energy delivered1 impact test #ce1jjj inch-pounds ,energy computed from static test 4#bf1djj ,efficiency of blow of hammer 4#ge4c per cent4 ,preparing the material3 ,the material used in making impact tests is of the same size and prepared in the same way as for static bending and compression tests4 ,bending in impact tests is more commonly used than compression1 and small beams with #bh-;inch span are usually employed4 ,method3 ,in making an impact bending test the hammer is allowed to rest upon the specimen and a zero or datum line is drawn4 ,the hammer is then dropped from increasing heights and drum records taken until first failure4 ,the first drop is one inch and the increase is by increments of one inch until a height of ten inches is reached1 after which increments of two inches are used until complete failure occurs or #f-;inch deflection is secured4 ,the #ej-pound hammer is used when with drops up to #fh inches it is reasonably certain it will produce complete failure or #f-;inch deflection in the case of all specimens of a species2 for all other species a #ajj-pound hammer is used4 ,results3 ,the tracing on the drum 7see ,fig4 #da7 represents the actual deflection of the stick and the subsequent rebounds for each drop4 ,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 paper1 with the height of drop in inches as the ordinate4 ,the elastic limit is that point on the diagram where the square of the deflection begins to increase more rapidly than the height of drop4 ,the difference between the datum line and the final resting point after each drop represents the set the material has received4 ,the formul 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 follows3 #c ,w ,h l 7#a7 r ----------- ,d b h#b ,f ,s l#b 7#b7 ,e ----------- #f ,d h ,w ,h 7#c7 ,s ------- l b h ,h height of drop of hammer1 including deflection1 inches4 ,s modulus of elastic resilience1 inch-pounds per cubic inch4 ,w weight of hammer1 pounds4 ,remainder of legend as in ,,bending ,,large ,,beams1 above4 ,,hardness ,,test3 ,,abrasion ,,and ,,indentation ,abrasion3 ,the machine used by the ,u4,s4 ,forest ,service is a modified form of the ,dorry abrasion machine4 7,see ,fig4 #db47 ,upon the revolving horizontal disk is glued a commercial sandpaper1 known as garnet paper1 which is commonly employed in factories in finishing wood4 ,illustration3 ,,fig4 #db4--;,abrasion machine for testing the wearing qualities of woods4 ,a small block of the wood to be tested is fixed in one clamp and a similar block of some wood chosen as a standard1 as sugar maple1 at #aj per cent moisture1 in the opposite1 and held against the same zone of sandpaper by a weight of #bf pounds each4 ,the size of the section under abrasion for each specimen is #b ,x #b4 ,the conditions for wear are the same for both specimens4 ,the speed of rotation is #fh revolutions a minute4 ,the test is continued until the standard specimen is worn a specified amount1 which varies with the kind of wood under test4 ,a comparison of the wear of the two blocks affords a fair idea of their relative resistance to abrasion4 ,another method makes use of a sand blast to abrade the woods and is the one employed in ,new ,south ,wales4#fj ,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 jet4 ,footnote #fj3 ,see ,warren1 ,w4,h43 ,the strength1 elasticity1 and other properties of ,new ,south ,wales hardwood timbers4 ,dept4 ,for41 ,n4,s4,w41 ,sydney1 #aiaa1 pp4 #hh-ie4 ,the wood to be tested is cut into blocks #c ,x #c ,x #a'1 and these are weighed to the nearest grain just before placing in the apparatus4 ,steam from the boiler at a pressure of about #dc 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 rotated4 ,only superheated steam strikes the block1 thus leaving the wood dry4 ,the test is continued for two minutes1 after which the specimen is removed and immediately weighed4 ,by comparison with the original weight the loss from abrasion is determined1 and by comparison with a certain wood chosen as a standard1 a coefficient of wear-resistance can be obtained4 ,the amount of wear will vary more or less according to the surface exposed1 and in these tests quarter-sawed material was used with the edge grain to the blast4 ,indentation3 ,the tool used for this test consists of a punch with a hemispherical end or steel ball having a diameter of #j4ddd inch1 giving a surface area of one-fourth square inch4 ,it is fitted with a guard plate1 which works loosely until the penetration has progressed to a depth of #j4bbb inch1 whereupon it tightens4 7,see ,fig4 #dc47 ,the effect is that of sinking a ball half its diameter into the specimen4 ,this apparatus is fitted into the movable head of the static testing machine4 ,illustration3 ,,fig4 #dc4--;,design of tool for testing the hardness of woods by indentation4 ,the wood to be tested is cut square with the grain into rectangular blocks measuring #b ,x #b ,x #f4 ,a block is placed on the platform and the end of the punch forced into the wood at the rate of #j4be inch per minute4 ,the operator keeps moving the small handle of the guard plate back and forth until it tightens4 ,at this instant the load is read and recorded4 ,two penetrations each are made on the tangential and radial surfaces1 and one on each end of every specimen tested4 ,in choosing the places on the block for the indentations1 effort should be made to get a fair average of heartwood and sapwood1 fine and coarse grain1 early and late wood4 ,another method of testing by indentation involves the use of a right-angled cone instead of a ball4 ,for details of this test as used in ,new ,south ,wales see loc4 cit41 pp4 #hf-hg4 ,,cleavage ,,test ,a static testing machine and a special cleavage testing device are required4 7,see ,fig4 #dd47 ,the latter consists essentially of two hooks1 one of which is suspended from the centre of the top of the cage1 the other extended above the movable head4 ,illustration3 ,,fig4 #dd4--;,design of tool for cleavage test4 ,the specimens are #b ,x #b ,x #c4ge4 ,at one end a one-inch hole is bored1 with its centre equidistant from the two sides and #j4be inch from the end4 7,see ,fig4 #de47 ,this makes the cross section to be tested #b ,x #c4 ,some of the blocks are cut radially and some tangentially1 as indicated in the figure4 ,illustration3 ,,fig4 #de4--;,design of cleavage test specimen4 ,the free ends of the hooks are fitted into the notch in the end of the specimen4 ,the movable head of the machine is then made to descend at the rate of #j4be inch per minute1 pulling apart the hooks and splitting the block4 ,the maximum load only is taken and the result expressed in pounds per square inch of width4 ,a piece one-half inch thick is split off parallel to the failure and used for moisture determination4 ,,tension ,,test ,,parallel ,,to ,,the ,,grain ,since the tensile strength of wood parallel to the grain is greater than the compressive strength1 and exceedingly greater than the shearing strength1 it is very difficult to make satisfactory tension tests1 as the head and shoulders of the test specimen 7which is subjected to both compression and shear7 must be stronger than the portion subjected to a pure tensile stress4 ,various designs of test specimens have been made4 ,the one first employed by the ,division of ,forestry#fa was prepared as follows3 ,sticks were cut measuring #a4e ,x #b4e ,x #af4 ,the thickness at the centre was then reduced to three-eighths of an inch by cutting out circular segments with a band saw4 ,this left a breaking section of #b4e ,x #j4cge4 ,care was taken to cut the specimen as nearly parallel to the grain as possible1 so that its failure would occur in a condition of pure tension4 ,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 two4 ,only the maximum load was recorded4 7,see ,fig4 #df1 ,no4 #a47 ,illustration3 ,,fig4 #df4--;,designs of tension test specimens used in ,united ,states4 ,footnote #fa3 ,bul4 ,no4 #h3 ,timber physics1 ,part ,,ii41 #ahic1 p4 #g4 ,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 ,u4,s4 ,forest ,service4 ,a form of specimen is suggested1 however1 and is as follows3 ,a rod of wood about one inch in diameter is bored by a hollow drill from the stick to be tested4 ,the ends of this rod are inserted and glued in corresponding holes in permanent hardwood wedges4 ,the specimen is then submitted to the ordinary tension test4 ,the broken ends are punched from the wedges4#fb 7,see ,fig4 #df1 ,no4 #b47 ,footnote #fb3 ,cir4 #ch3 ,instructions to engineers of timber tests1 #aijf1 p4 #bd4 ,the form used by the ,department of ,forestry of ,new ,south ,wales#fc is as shown in ,fig4 #dg4 ,the specimen has a total length of #da inches and is circular in cross section4 ,on each end is a head #d inches in diameter and #g inches long4 ,below each head is a shoulder #h4e inches long1 which tapers from a diameter of #b4ge inches to #a4be inches4 ,in the middle is a cylindrical portion #a4be inches in diameter and #aj inches long4 ,illustration3 ,,fig4 #dg4--;,design of tension test specimen used in ,new ,south ,wales4 ,footnote #fc3 ,warren1 ,w4,h43 ,the strength1 elasticity1 and other properties of ,new ,south ,wales hardwood timbers1 #aiaa1 pp4 #eh-fb4 ,in making the test the specimen is fitted in the machine1 and an extensometer attached to the middle portion and arranged to record the extension between the gauge points #h inches apart4 ,the area of the cross section then is #a4bbf square inches1 and the tensile strength is equal to the total breaking load applied divided by this area4 ,,tension ,,test ,,at ,,right ,,angles ,,to ,,the ,,grain ,a static testing machine and a special testing device 7see ,fig4 #dh7 are required4 ,the latter consists essentially of two double hooks or clamps1 one of which is suspended from the centre of the top of the cage1 the other extended above the movable head4 ,the specimens are #b ,x #b ,x #b4e4 ,at each end a one-inch hole is bored with its centre equidistant from the two sides and #j4be inch from the ends4 ,this makes the cross section to be tested #a ,x #b4 ,illustration3 ,,fig4 #dh4--;,design of tool and specimen for testing tension at right angles to the grain4 ,the free ends of the clamps are fitted into the notches in the ends of the specimen4 ,the movable head of the machine is then made to descend at the rate of #j4be inch per minute1 pulling the specimen in two at right angles to the grain4 ,the maximum load only is taken and the result expressed in pounds per inch of width4 ,a piece one-half inch thick is split off parallel to the failure and used for moisture determination4 ,,torsion ,,test#fd ,footnote #fd3 ,wood is so seldom subjected to a pure stress of this kind that the torsion test is usually omitted4 ,apparatus3 ,the torsion test is made in a ,riehle-,miller torsional testing machine or its equivalent4 7,see ,fig4 #di47 ,illustration3 ,,fig4 #di4--,making a torsion test on hickory4 ,preparation of material3 ,the test pieces are cylindrical1 #a4e inches in diameter and #ah inches gauge length1 with squared ends #d inches long joined to the cylindrical portion with a fillet4 ,the dimensions are carefully measured1 and the usual data obtained in regard to the rate of growth1 proportion of late wood1 location and kind of defects4 ,the weight of the cylindrical portion of the specimen is obtained after the test4 ,making the test3 ,after the specimen is fitted in the machine the load is applied continuously at the rate of #bb per minute4 ,a troptometer is used in measuring the deformation4 ,readings are made until failure occurs1 the points being entered on the cross-section paper4 ,the character of the failure is described4 ,moisture determinations are made by the disk method4 ,results3 ,the conditions of ultimate rupture due to torsion appear not to be governed by definite mathematical laws2 but where the material is not overstrained1 laws may be assumed which are sufficiently exact for practical cases4 ,the formul commonly used for computations are as follows3 #e4a ,m 7#a7 ,t ------- c#c #aad4f ,t f 7#b7 ,g ----------- a c a angle measured by troptometer at elastic limit1 in degrees4 c diameter of specimen1 inches4 f gauge length of specimen1 inches4 ,g modulus of elasticity in shear across the grain1 pounds per square inch4 ,m moment of torsion at elastic limit1 inch-pounds4 ,t outer fibre torsional stress at elastic limit1 pounds per square inch4 ,,special ,,tests ,spike-pulling ,test ,spike-pulling tests apply to problems of railroad maintenance1 and the results are used to compare the spike-holding powers of various woods1 both untreated and treated with different preservatives1 and the efficiency of various forms of spikes4 ,special tests are also made in which the spike is subjected to a transverse load applied repetitively by a blow4 ,for details of tests and results see3 ,cir4 #ch1 ,u4,s4,f4,s43 ,instructions to engineers of timber tests1 p4 #bf4 ,cir4 #df1 ,u4,s4,f4,s43 ,holding force of railroad spikes in wooden ties4 ,bul4 #aah1 ,u4,s4,f4,s13 ,prolonging the life of cross-ties1 pp4 #cg-dj4 ,packing ,boxes ,special tests on the strength of packing boxes of various woods have been made by the ,u4,s4 ,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 use4 ,the methods of tests consisted in applying a load along the diagonal of a box1 an action similar to that which occurs when a box is dropped on one of its corners4 ,the load was measured at each one-fourth inch in deflection1 and notes were made of the primary and subsequent failures4 ,for details of tests and results1 see3 ,cir4 #dg1 ,u4,s4,f4,s43 ,strength of packing boxes of various woods4 ,cir4 #bad1 ,u4,s4,f4,s43 ,tests of packing boxes of various forms4 ,vehicle and ,implement ,woods ,tests were made by the ,u4,s4 ,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 them4 ,tests were made upon the following materials3 hickory buggy spokes 7see ,fig4 #e72 hickory and red oak buggy shafts2 wagon tongues2 ,douglas fir and southern pine cultivator poles4 ,details of the tests and results may be found in3 ,cir4 #adb1 ,u4,s4,f4,s43 ,tests on vehicle and implement woods4 ,cross-arms ,in tests by the ,u4,s4 ,forest ,service on cross-arms a special apparatus was devised in which the load was distributed along the arm as in actual practice4 ,the load was applied by rods passing through the pinholes in the arms4 ,nuts on these rods pulled down on the wooden bearing-blocks shaped to fit the upper side of the arm4 ,the lower ends of these rods were attached to a system of equalizing levers1 so arranged that the load at each pinhole would be the same4 ,in all the tests the load was applied vertically by means of the static machine4 ,see ,cir4 #bjd1 ,u4,s4,f4,s43 ,strength tests of cross-arms4 ,other ,tests ,many other kinds of tests are made as occasion demands4 ,one kind consists of barrels and liquid containers1 match-boxes1 and explosive containers4 ,these articles are subjected to shocks such as they would receive in transit and in handling1 and also to hydraulic pressure4 ,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 together1 mortised joints1 wooden trusses1 etc4 ,tests of this kind can best be worked out according to the specific requirements in each case4 ,,appendix ,,sample ,,working ,,plan ,,of ,,the ,u4,s4 ,,forest ,,service ,,mechanical ,,properties ,,of ,,woods ,,grown ,,in ,,the ,,united ,,states ,working ,plan ,no4 #abd ,,purpose ,,of ,,work ,it is the general purpose of the work here outlined to provide3 7a7 ,reliable data for comparing the mechanical properties of various species2 7b7 ,data for the establishment of correct strength functions or working stresses2 7c7 ,data upon which may be based analyses of the influence on the mechanical properties of such factors as3 ,locality2 ,distance of timber from the pith of the tree2 ,height of timber in the tree2 ,change from the green to the air-dried condition1 etc4 ,the mechanical properties which will be considered and the principal tests used to determine them are as follows3 ,strength and stiffness-- ,static bending2 ,compression parallel to grain2 ,compression perpendicular to grain2 ,shear4 ,toughness-- ,impact bending2 ,static bending2 ,work to maximum load and total work4 ,cleavability-- ,cleavage test4 ,hardness-- ,modification of ,janka ball test for surface hardness4 ,,material ,selection and ,number of ,trees ,the material will be from trees selected in the forest by one qualified to determine the species4 ,from each locality1 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 species4 ,each species will eventually be represented by trees from five to ten localities4 ,these localities will be so chosen as to be representative of the commercial range of the species4 ,trees from one to three localities will be used to represent each species until most of the important species have been tested4 ,the #af-;foot butt log will be taken from each tree selected and the entire merchantable hole of one average tree for each species4 ,field ,notes and ,shipping ,instructions ,field notes as outlined in ,form--a ,shipment ,description1 ,manual of the ,branch of ,products1 will be fully and carefully made by the collector4 ,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 notes4 ,each log will have the bark left on4 ,it will be plainly marked in accordance with directions given under ,detailed ,instructions4 ,all material will be shipped to the laboratory immediately after being cut4 ,no trees will be cut until the collector is notified that the laboratory is ready to receive the material4 ,,detailed ,,instructions ,part of ,tree to be ,tested 7a7 ,for determining the value of tree and locality and the influence on the mechanical properties of distance from the pith1 a #d-;foot bolt will be cut from the top end of each #af-;foot butt log4 7b7 ,for investigating the variation of properties with the height of timber in the tree1 all the logs from one average tree will be used4 7c7 ,for investigating the effect of drying the wood1 the bolt next below that provided for in 7a7 will be used in the case of one tree from each locality4 ,marking and ,grouping of ,material ,the marking will be standard except as noted4 ,each log will be considered a piece4 ,the piece numbers will be plainly marked upon the butt end of each log by the collector4 ,the north side of each log will also be marked4 ,when only one bolt from a tree is used it will be designated by the number of the log from which it is cut4 ,whenever more than one bolt is taken from a tree1 each #d-;foot bolt or length of trunk will be given a letter 7mark71 a1 b1 c1 etc41 beginning at the stump4 ,all bolts will be sawed into #b-a_/b ,x #b-a_/b sticks and the sticks marked according to the sketch1 ,fig4 #ej4 ,the letters ,n1 ,e1 ,s1 and ,w indicate the cardinal points when known2 when these are unknown1 ,h1 ,k1 ,l1 and ,m will be used4 ,thus1 ,n#e1 ,k#h1 ,s#g1 ,m#d are stick numbers1 the letter being a part of the stick number4 ,illustration3 ,,fig4 #ej4--,method of cutting and marking test specimens4 ,only straight-grained specimens1 free from defects which will affect their strength1 will be tested4 ,care of ,material ,no material will be kept in the bolt or log long enough to be damaged or disfigured by checks1 rot1 or stains4 ,green material3 ,the material to be tested green will be kept in a green state by being submerged in water until near the time of test4 ,it will then be surfaced1 sawed to length1 and stored in damp sawdust at a temperature of #gj;,f4 7as nearly as practicable7 until time of test4 ,care should be taken to avoid as much as possible the storage of green material in any form4 ,air-dry material3 ,the material to be air-dried will be cut into sticks #b-a_/b ,x #b-a_/b ,x #d'4 ,the ends of these sticks will be paraffined to prevent checking4 ,this material will be so piled as to leave an air space of at least one-half inch on each side of each stick1 and in such a place that it will be protected from sunshine1 rain1 snow1 and moisture from the ground4 ,the sticks will be surfaced and cut to length just previous to test4 ,order of ,tests ,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 conditions4 ,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 tree4 ,tests on ,green ,material ,the tests on all bolts1 except those from which a comparison of green and dry timber is to be gotten1 will be as follows3 ,static bending3 ,one stick from each pair4 ,a pair consists of two adjacent sticks equidistant from the pith1 as ,n#g and ,n#h1 or ,h#e and ,h#f4 ,impact bending3 ,four sticks2 one to be taken from near the pith2 one from near the periphery2 and two representative of the cross section4 ,compression parallel to grain3 ,one specimen from each stick4 ,these will be marked #a in addition to the number of the stick from which they are taken4 ,compression perpendicular to grain3 ,one specimen from each of #ej per cent of the static bending sticks4 ,these will be marked #b in addition to the number of the stick from which they are cut4 ,hardness3 ,one specimen from each of the other #ej per cent of the static bending sticks4 ,these specimens will be marked #d4 ,shear3 ,six specimens from sticks not tested in bending or from the ends cut off in preparing the bending specimens4 ,two specimens will be taken from near the pith2 two from near the periphery2 and two that are representative of the average growth4 ,one of each two will be tested in radial shear and the other in tangential shear4 ,these specimens will have the mark #c4 ,cleavage3 ,six specimens chosen and divided just as those for shearing4 ,these specimens will have the mark #e4 7,for sketches showing radial and tangential cleavage1 see ,fig4 #de47 ,when it is impossible to secure clear specimens for all of the above tests1 tests will have precedence in the order in which they are named4 ,tests to ,determine the ,effect of ,air-drying ,these tests will be made on material from the adjacent bolts mentioned in c under ,part of ,tree to be ,tested4 ,both bolts will be cut as outlined above4 ,one-half the sticks from each bolt will be tested green1 the other half will be air-dried and tested4 ,the division of green and air-dry will be according to the following scheme3 ,,stick ,,numbers ,lower bolt1 #a1 #d1 #e1 #h1 #i1 ,tested etc4 green ,upper bolt1 #b1 #c1 #f1 #g1 #aj1 ,lower bolt1 #b1 #c1 #f1 #g1 #aj1 ,air-dried etc4 and ,upper bolt1 #a1 #d1 #e1 #h1 #i1 tested ,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 bolts4 ,the tests on the air-dried material will be the same as on the green except for the difference of seasoning4 ,the material will be tested at as near #ab per cent moisture as is practicable4 ,the approximate weight of the air-dried specimens at #ab per cent moisture will be determined by measuring while green #bj per cent of the sticks to be air-dried and assuming their dry gravity to be the same as that of the specimens tested green4 ,this #bj per cent will be weighed as often as is necessary to determine the proper time of test4 ,methods of ,test ,all tests will be made according to ,circular #ch except in case of conflict with the instructions given below3 ,static bending3 ,the tests will be on specimens #b ,x #b ,x #cj on #bh-;inch span4 ,load will be applied at the centre4 ,in all tests the load-deflection curve will be carried to or beyond the maximum load4 ,in one-third of the tests the load-deflection curve will be continued to #f-;inch deflection1 or till the specimen fails to support a #bjj-pound load4 ,deflection readings for equal increments of load will be taken until well past the elastic limit1 after which the scale beam will be kept balanced and the load read for each #j4a-;inch deflection4 ,the load and deflection at first failure1 maximum load and points of sudden change1 will be shown on the curve sheet even if they do not occur at one of the regular load or deflection increments4 ,impact bending3 ,the impact bending tests will be on specimens of the same size as those used in static bending4 ,the span will be #bh inches4 ,the tests will be by increment drop4 ,the first drop will be #a inch and the increase will be by increments of #a inch till a height of #aj inches is reached1 after which increments of #b inches will be used until complete failure occurs or #f-;inch deflection is secured4 ,a #ej-pound hammer will be used when with drops up to #fh inches it is practically certain that it will produce complete failure or #f-;inch deflection in the case of all specimens of a species4 ,for all other species1 a #ajj-pound hammer will be used4 ,in all cases drum records will be made until first failure4 ,also the height of drop causing complete failure or #f-;inch deflection will be noted4 ,compression parallel to grain3 ,this test will be on specimens #b ,x #b ,x #h in size4 ,on #bj per cent of these tests load-compression curves for a #f-;inch centrally located gauge length will be taken4 ,readings will be continued until the elastic limit is well passed4 ,the other #hj per cent of the tests will be made for the purpose of obtaining the maximum load only4 ,compression perpendicular to grain3 ,this test will be on specimens #b ,x #b ,x #f in size4 ,the bearing plates will be #b inches wide4 ,the rate of descent of the moving head will be #j4jbd inch per minute4 ,the load-compression curve will be plotted to #j4a inch compression and the test will then be discontinued4 ,hardness3 ,the tool shown in ,fig4 #dc 7an adaptation of the apparatus used by the ,german investigator1 ,janka7 will be used4 ,the rate of descent of the moving head will be #j4be inch per minute4 ,when the penetration has progressed to the point at which the plate a becomes tight1 due to being pressed against the wood1 the load will be read and recorded4 ,two penetrations will be made on a tangential surface1 two on a radial1 and one on each end of each specimen tested4 ,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 sap1 slow and fast growth1 and spring and summer wood4 ,specimens will be #b ,x #b ,x #f4 ,shear3 ,the tests will be made with a tool slightly modified from that shown in ,circular #ch4 ,the speed of descent of head will be #j4jae inch per minute4 ,the only measurements to be made are those of the shearing area4 ,the offset will be #a_/h inch4 ,specimens will be #b ,x #b ,x #b-a_/b in size4 7,for definition of offset and form of test specimen1 see ,fig4 #ch47 ,cleavage3 ,the cleavage tests will be made on specimens of the form and size shown in ,fig4 #de4 ,the apparatus will be as shown in ,fig4 #dd4 ,the maximum load only will be taken and the result expressed in pounds per inch of width4 ,the speed of the moving head will be #j4be inch per minute4 ,moisture ,determinations ,moisture determinations will be made on all specimens tested except those to be photographed or kept for exhibit4 ,a #a-;inch disk will be cut from near the point of failure of bending and compression parallel specimens1 from the portion under the plate in the case of the compression perpendicular specimens1 and from the centre of the hardness test specimens4 ,the beads from the shear specimens will be used as moisture disks4 ,in the case of the cleavage specimens a piece #a_/b inch thick will be split off parallel to the failure and used as a moisture disk4 ,,records ,all records will be standard4 ,,photographs ,cross ,sections ,just before cutting into sticks1 the freshly cut end of at least one bolt from each tree will be photographed4 ,a scale of inches will be shown in this photograph4 ,specimens ,three photographs will be made of a group consisting of four #b ,x #b ,x #cj specimens chosen from the material from each locality4 ,two of these specimens will be representative of average growth1 one of fast and one of slow growth4 ,these photographs will show radial1 tangential1 and end surfaces for each specimen4 ,failures ,typical and abnormal failures of material from each site will be photographed4 ,disposition of ,material ,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 value4 ,,shrinkage ,,and ,,specific ,,gravity ,appendix to ,working ,plan #abd ,,purpose ,,of ,,work ,it is the purpose of this work to secure data on the shrinkage and specific gravity of woods tested under ,project #abd4 ,the figures to be obtained are for use as average working values rather than as the basis for a detailed study of the principles involved4 ,,material ,the material will be taken from that provided for mechanical tests4 ,,radial ,,and ,,tangential ,,shrinkage ,specimens ,preparation3 ,two specimens #a inch thick1 #d inches wide1 and #a inch long will be obtained from near the periphery of each d bolt4 ,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 bolt4 ,they will be taken from adjoining pieces chosen so that the results will be comparable for use in determining radial and tangential shrinkage4 7,when a disk is used1 care must be taken that it is green and has not been affected by the shrinkage and checking near the end of the bolt47 ,one of these specimens will be cut with its width in the radial direction and will be used for the determination of radial shrinkage4 ,the other will have its width in the tangential direction and will be used for tangential shrinkage4 ,these specimens will not be surfaced4 ,marking3 ,the shrinkage specimens will retain the shipment and piece numbers and marks of the bolts from which they are taken1 and will have the additional mark #g,r or #g,t according as their widths are in the radial or tangential direction4 ,shrinkage measurements3 ,the shrinkage specimens will be carefully weighed and measured soon after cutting4 ,rings per inch1 per cent sap1 and per cent summer wood will be measured4 ,they will then be air-dried in the laboratory to constant weight1 and afterward oven-dried at #ajj;,c4 7#bab;,f471 when they will again be weighed and measured4 ,,volumetric ,,shrinkage ,,and ,,specific ,,gravity ,specimens ,selection and preparation3 ,four #b ,x #b ,x #f specimens will be cut from the mechanical test sticks of each d bolt2 also from each of the composite bolts used in getting a comparison of green and air-dry4 ,one of these specimens will be taken from near the pith and one from near the periphery2 the other two will be representative of the average growth of the bolt4 ,the sides of these specimens will be surfaced and the ends smooth sawn4 ,marking3 ,each specimen will retain the shipment1 piece1 and stick numbers and mark of the stick from which it is cut1 and will have the additional mark ,s4 ,manipulation3 ,soon after cutting1 each specimen will be weighed and its volume will be determined by the method described below4 ,the rings per inch and per cent summer wood1 where possible1 will be determined1 and a carbon impression of the end of the specimen made4 ,it will then be air-dried in the laboratory to a constant weight and afterward oven-dried at #ajj;,c4 ,when dry1 the specimen will be taken from the oven1 weighed1 and a carbon impression of its end made4 ,while still warm the specimen will be dipped in hot paraffine4 ,the volume will then be determined by the following method3 ,on one pan of a pair of balances is placed a container having in it water enough for the complete submersion of the test specimen4 ,this container and water is balanced by weights placed on the other scale pan4 ,the specimen is then held completely submerged and not touching the container while the scales are again balanced4 ,the weight required to balance is the weight of water displaced by the specimen1 and hence if in grams is numerically equal to the volume of the specimen in cubic centimetres4 ,a diagrammatic sketch of the arrangement of this apparatus is shown in ,fig4 #ea4 ,illustration3 ,,fig4 #ea4--;,diagram of specific gravity apparatus1 showing a balance with container 7c7 filled with water in which the test block 7b7 is held submerged by a light rod 7a7 which is adjustable vertically and provided with a sharp point to be driven into the specimen4 ,air-dry specimens will be dipped in water and then wiped dry after the first weighing and just before being immersed for weighing their displacement4 ,all displacement determinations will be made as quickly as possible in order to minimize the absorption of water by the specimen4 ,,strength ,,values ,,for ,,structural ,,timbers 7,from ,cir4 #ahi1 ,u4,s4 ,forest ,service7 ,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 ,states4 ,these results are more completely discussed in other publications of the ,service1 a list of which is given in ,,bibliography1 ,,part ,,iii4 ,the tests were made at the laboratories of the ,u4,s4 ,forest ,service1 in cooperation with the following institutions3 ,yale ,forest ,school1 ,purdue ,university1 ,university of ,california1 ,university of ,oregon1 ,university of ,washington1 ,university of ,colorado1 and ,university of ,wisconsin4 ,tables ,,xviii and ,,xix give the average results obtained from tests on green material1 while ,tables ,,xx and ,,xxi give average results from tests on air-seasoned material4 ,the small specimens1 which were invariably #b ,x #b in cross section1 were free from defects such as knots1 checks1 and cross grain2 all other specimens were representative of material secured in the open market4 ,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 #b ,x #b4 ,tests to determine the mechanical properties of different species are often confined to small1 clear specimens4 ,the ratios included in the tables may be applied to such results in order to approximate the strength of the species in structural sizes1 and containing the defects usually encountered1 when tests on such forms are not available4 ,a comparison of the results of tests on seasoned material with those from tests on green material shows that1 without exception1 the strength of the #b ,x #b specimens is increased by lowering the moisture content1 but that increase in strength of other sizes is much more erratic4 ,some specimens1 in fact1 show an apparent loss in strength due to seasoning4 ,if structural timbers are seasoned slowly1 in order to avoid excessive checking1 there should be an increase in their strength4 ,in the light of these facts it is not safe to base working stresses on results secured from any but green material4 ,for a discussion of factors of safety and safe working stresses for structural timbers see the ,manual of the ,american ,railway ,engineering ,association1 ,chicago1 #aiaa4 ,a table from that publication1 giving working unit stresses for structural timber1 is reproduced in this book1 see ,table ,,xxii4 ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------- ,,table ,,xviii ,,table ,,xviii ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------- ,,bending ,,tests ,,on ,,green ,,material ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------- ,sizes ,f4,s4 at ,e4,l4 ,m4 of ,r4 ,m4 of ,e4 ,calculated ----------------- ,num- ,per ,rings shear ,species ber cent per ---------------------------------------- ---------------------------- ,cross ,span of mois- inch ,average ,ratio ,average ,ratio ,average ,ratio ,average ,ratio ,section tests ture per sq4 to #b per sq4 to #b per sq4 to #b per sq4 to #b inch by #b inch by #b inch by #b inch by #b ---------------------------------------- ---------------------------------------- -------------------------------------- #a1jjj ,inches ,ins4 ,lbs4 ,lbs4 lbs4 ,lbs4 ,longleaf pine #ab by #ab #ach #d #bh4f #i4g #d1jbi #j4hc #f1gaj #j4gd #a1ebc #j4ii #bfa #j4hf #aj by #af #afh #d #bf4h #af4g #f1dec 4#he #f1dec 4#ga #a1fbf #a4je #cjf #a4ja #h by #af #aef #g #bh4d #ad4f #c1adg 4#fd #e1dci 4#fj #a1cfh 4#hi #cij #a4bi #f by #af #acb #a #dj4c #ba4h #d1abj 4#hc #f1dfj 4#ga #a1aij 4#gg #cgh #a4be #f by #aj #ahj #a #ca4j #f4b #c1ehj 4#gb #f1ejj 4#gb #a1dab 4#ib #age 4#eh #f by #h #ahj #b #bg4j #h4b #c1gce 4#ge #e1gde 4#fc #a1bhb 4#hc #aba 4#dj #b by #b #cj #ae #cc4i #ad4a #d1iej #a4jj #i1jgj #a4jj #a1edj #a3jj #cjc #a4jj ,douglas fir #h by #af #ahj #aia #ca4e #aa4j #c1ifh 4#gf #e1ihc 4#gb #a1eag 4#ie #bfi 4#ha #e by #h #ahj #hd #cj4a #aj4h #c1fic 4#ga #e1agh 4#fc #a1ecc 4#if #agb 4#eb #b by #ab #ahj #bg #ce4g #bj4c #c1gba 4#ga #e1bgf 4#fd #a1fdb #a4jc #bef 4#gg #b by #aj #ahj #bf #cb4i #ba4f #c1afj 4#fj #d1fii 4#eg #a1eic #a4jj #ahi 4#eg #b by #h #ahj #bi #cc4f #ag4f #c1eic 4#fi #e1ceb 4#fe #a1fjg #a4ja #aga 4#ea #b by #b #bd #efh #cj4d #aa4f #e1bbg #a4jj #i1jgj #a4jj #a1edj #a4jj #cjc #a4jj ,douglas fir 7fire-killed7 #h by #af #ahj #cj #cf4h #aj4i #c1ejc 4#hj #d1iid 4#fd #a1eca 4#id #ccj #a4ai #b by #ab #ahj #cb #cd4b #ag4g #c1dhi 4#hj #e1jhe 4#ff #a1fbd 4#ii #bdg 4#hi #b by #aj #ahj #cb #ch4i #ah4a #c1hea 4#hh #e1cei 4#fi #a1gaf #a4je #baf 4#gh #b by #h #ahj #ca #cg4j #ae4g #c1djc 4#gh #e1cje 4#fh #a1fgf #a4jb #afi 4#fa #b by #b #cj #bij #cc4b #ag4b #d1cfj #a4jj #g1geb #a4jj #a1fcf #a4jj #bgg #a4jj ,shortleaf pine #h by #af #ahj #ab #ci4e #ab4a #c1ahe 4#gc #e1djg 4#gj #a1dch #a4jc #cfb #a4dj #h by #ad #ahj #ab #de4h #ab4g #c1bcd 4#gd #e1gha 4#ge #a1did #a4jg #cch #a4ca #h by #ab #ahj #bd #eb4b #aa4h #c1bfe 4#ge #e1ejc 4#ga #a1dhj #a4jf #bgg #a4jg #e by #h #ahj #bd #dg4h #aa4e #c1eai 4#ha #e1gcb 4#gd #a1dhe #a4jf #ahe 4#gb #b by #b #cj #bed #ea4g #ac4f #d1cej #a4jj #g1gaj #a4jj #a1cie #a4jj #beh #a4jj ,western larch #h by #af #ahj #cb #ea4j #be4c #c1bgf 4#gg #d1fcb 4#fd #a1bgb 4#ig #bih #a4aa #h by #ab #ahj #cj #ej4c #bc4b #c1cgf 4#gi #e1bhf 4#gc #a1cca #a4jb #bed 4#id #e by #h #ahj #ad #ef4j #be4f #c1ebh 4#hc #e1cca 4#gd #a1dcb #a4ji #afi 4#fc #b by #b #bh #ahi #df4b #bf4b #d1bgd #a4jj #g1bea #a4jj #a1caj #a4jj #bfi #a4jj ,loblolly pine #h by #af #ahj #ag #ae4h #f4a #c1jid 4#ge #e1cid 4#fi #a1djf 4#ih #chc #a4dd #e by #ab #ahj #id #fj4i #e4i #c1jcj 4#gd #e1jbh 4#fd #a1chc 4#if #bba 4#hc #b by #b #cj #dd #gj4i #e4d #d1ajj #a4jj #g1hgj #a4jj #a1ddj #a4jj #bfe #a4jj ,tamarack #f by #ab #afb #ae #eg4f #af4f #b1iad 4#ge #d1ejj 4#ff #a1bjb #a4je #bee #a4aa #d by #aj #afb #ae #dc4e #aa4d #b1gab 4#gj #d1faa 4#fh #a1bch #a4jh #bji 4#ia #b by #b #cj #hb #ch4h #ad4j #c1hge #a4jj #f1hbj #a4jj #a1ada #a4jj #bbi #a4jj ,western hemlock #h by #af #ahj #ci #db4e #ae4f #c1eaf 4#hj #e1bif 4#gc #a1dde #a4ja #bfa 4#ib #b by #b #bh #eb #ea4h #ab4a #d4djf #a4jj #g1bid #a4jj #a1dbh #a4jj #bhd #a4jj ,redwood #h by #af #ahj #ad #hf4e #ai4i #c1gcd 4#gi #d1dib 4#fd #a1jaf 4#if #cjj #a4ba #f by #ab #ahj #ad #hg4c #ag4h #c1ghg 4#hj #d1dea 4#fd #a1jfh #a4jj #bbd 4#ij #g by #i #ahj #ad #gi4h #af4g #d1dab 4#ic #e1bgi 4#gf #a1cbd #a4be #aii 4#hj #c by #ad #ahj #ac #hf4a #bc4g #c1ejf 4#gd #d1cfd 4#fb #idg 4#hi #bee #a4jc #b by #ab #ahj #ab #gj4i #ah4f #c1ajj 4#fe #c1gec 4#ed #a1jeb 4#ii #ahg 4#ge #b by #aj #ahj #ac #ee4h #bj4j #c1bhe 4#fi #d1jgi 4#eh #a1ajg #a4jd #afi 4#fh #b by #h #ahj #ac #fc4h #ba4e #b1ihi 4#fc #d1jfc 4#eh #a1ada #a4jh #acd 4#ed #b by #b #bh #aeg #ge4e #ai4a #d1gej #a4jj #f1ihj #a4jj #a1jfa #a4jj #bdh #a4jj ,norway pine #f by #ab #afb #ae #ej4c #ab4e #b1cje 4#hb #c1egb 4#fi #ihg #a4jc #bja #a4ag #d by #ab #afb #ah #dg4i #ad4g #b1fdh 4#id #d1ajg 4#gi #a1bee #a4ca #bch #a4ch #d by #aj #afb #af #de4g #ac4c #b1fgd 4#ie #d1bje 4#ha #a1cjf #a4cf #aih #a4ae #b by #b #cj #acc #cb4c #aa4d #b1hjh #a4jj #e1agc #a4jj #ifj #a4jj #agb #a4jj ,red spruce #b by #aj #add #ad #cb4e #ba4i #b1cid 4#ff #c1eff 4#fj #a1ahj #a4jb #aha 4#hj #b by #b #bf #fj #cg4c #ba4c #c1fbg #a4jj #e1ijj #a4jj #a1aeg #a4jj #bbg #a4jj ,white spruce #b by #aj #add #af #dj4g #i4c #b1bci 4#gb #c1bhh 4#fc #a1jha #a4jh #aff 4#hc #b by #b #bf #hc #eh4c #aj4b #c4jij #a4jj #e1ahe #a4jj #iih #a4jj #aii #a4jj ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------- ,note4--,following is an explanation of the abbreviations used in the foregoing tables3 ,f4,s4 at ,e4,l4 ,fiber stress at elastic limit4 ,m4 of ,e4 ,modulus of elasticity4 ,m4 of ,r4 ,modulus of rupture4 ,cr4 str4 at ,e4,l4 ,crushing strength at elastic limit4 ,cr4 str4 at max4 ld4 ,crushing strength at maximum load4 ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------------------- ,,table ,,xix ,,table ,,xix ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------------------- ,,compression ,,and ,,shear ,,tests ,,on ,,green ,,material ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------------------- ,compression ,compression ,shear parallel to grain perpendicular to grain ---------------------------------------- ---------------------------------------- ---------------------------------------- --- ,cr4 ,cr4 ,cr4 ,species ,per str4 ,m4 of str4 ,per str4 ,per ,size of ,no4 cent at ,e4 at max4 ,stress ,no4 cent at max4 ,no4 cent ,shear specimen of of ,e4 ,l4 per ld414 area ,height of of ld41 of of strength tests mois- per square per tests mois- per tests mois- ture square inch square ture square ture inch inch inch ---------------------------------------- ---------------------------------------- --------- --------------------------------------- #a1jjj ,inches ,lbs4 lbs4 ,lbs4 ,inches ,inches ,lbs4 ,lbs4 ,longleaf pine #d by #d #df #bf4c #c1dhj #d1hjj #d by #d #d #bb #be4c #efh #dd #ba4h #igc #b by #b #ad #cd4g #d1djj ,douglas fir #f by #f #eae #cj4g #b1ghj #a1aha #c1ejj #d by #h #af #bei #cj4c #egj #eca #bi4g #gfe #e by #f #agj #cj4i #b1gbj #b1abc #c1dij #b by #b #ijb #bi4h #c1ejj #a1ibe #d1jcj ,douglas fir 7fire-killed7 #f by #f #ajh #cd4h #b1fbj #a1hja #c1bij #f by #h #af #bd #cc4g #cfh #gg #ce4h #fca #b by #b #bjd #cg4i #c1dcj ,shortleaf pine #f by #f #ie #da4b #b1ead #a1efe #c1dcf #e by #h #af #ab #cg4g #cfa #agi #dg4j #gjd #e by #h #bc #dc4e #b1bda #a1ebi #c1dbc #e by #h #ad #ab #db4h #cff #b by #b #bha #ea4d #c1egj #e by #h #ab #bd #ec4j #cbe #e by #e #h #bd #dg4j #cdd #b by #b #b #bgg #dh4e #djj ,western larch #f by #f #ajg #di4a #b1fge #a1ege #c1eaj #f by #h #af #bb #dc4f #dag #agi #dj4g #gjj #b by #b #dia #ej4f #c1jbf #a1ede #c1fif #f by #h #ab #bj #dj4b #daf #d by #f #f #ec #eb4h #dgh #d by #d #d #cj #ej4d #dgb ,loblolly pine #h by #h #ad #fc4d #a1efj #cfe #b1adj #h by #d #h #af #fg4b #cib #aba #hc4b #fcj #d by #h #ah #fj4j #b1dcj #fia #c1efj #d by #d #h #ch #dd4f #edf #b by #b #ec #gd4j #c1bdj ,tamarack #f by #g #d #di4i #b1ccb #a1dcb #c1jcb #bd #ci4b #ffh #d by #g #f #bg4g #b1ddd #a1ccd #c1cfj #b by #b #afe #cf4h #c1aij ,western hemlock #f by #f #hb #df4f #b1ije #a1fag #c1cee #f by #d #f #cj #dh4g #dcd #ed #fe4g #fcj #b by #b #aca #ee4f #b1ich #a1gcg #c1cib ,redwood #f by #f #cd #hc4f #c1aid #a1bdj #c1hhb #f by #h #af #ac #hf4g #dgc #adh #hd4b #gdb #b by #b #adc #cf4h #c1dij #a1bbb #c1ihj #f by #f #ab #ad #hc4j #dbd #f by #g #i #ac #gd4g #dgg #f by #c #ad #ac #ge4f #daa #f by #b #ab #ab #ff4e #dcj #f by #b #aj #aa #ee4j #dbc #f by #b #h #ab #ef4g #cif #b by #b #b #ahf #ge4e #efi ,norway pine #f by #g #e #bi4j #a1ibh #ije #b1djd #bj #bf4g #ehi #d by #g #h #bh4d #b1aed #a1jfc #b1feb #b by #b #agh #bf4h #b1ejd ,red spruce #b by #b #eh #ce4d #b1gej #b by #b #b #dc #ca4h #caj #cj #cb4j #geh ,white spruce #b by #b #hd #fa4j #b1cgj #b by #b #b #df #ej4d #bgj #dj #eh4j #fea ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------------------- ,note4--,following is an explanation of the abbreviations used in the foregoing tables3 ,f4,s4 at ,e4,l4 ,fiber stress at elastic limit4 ,m4 of ,e4 ,modulus of elasticity4 ,m4 of ,r4 ,modulus of rupture4 ,cr4 str4 at ,e4,l4 ,crushing strength at elastic limit4 ,cr4 str4 at max4 ld4 ,crushing strength at maximum load4 ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------- ,,table ,,xx ,,table ,,xx ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------- ,,bending ,,tests ,,on ,,air-,,seasoned ,,material ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------- ,sizes ,f4,s4 at ,e4,l4 ,m4 of ,r4 ,m4 of ,e4 ,calculated ----------------- ,num- ,per ,rings shear ,species ber cent per ---------------------------------------- ---------------------------- ,cross ,span of mois- inch ,average ,ratio ,average ,ratio ,average ,ratio ,average ,ratio ,section tests ture per sq4 to #b per sq4 to #b per sq4 to #b per sq4 to #b inch by #b inch by #b inch by #b inch by #b ---------------------------------------- ---------------------------------------- -------------------------------------- #a1jjj ,inches ,ins4 ,lbs4 ,lbs4 lbs4 ,lbs4 ,longleaf pine #h by #af #ahj #e #bb4b #af4j #c1cij #j4ej #d1bgd #j4cg #a1gdg #a4jj #bhh #j4ge #f by #af #acb #a #bc4d #ag4a #c1dgj 4#ea #f1faj 4#eg #a1eja 4#hf #chh #a4ja #f by #aj #agg #b #ai4j #h4h #d1efj 4#fh #g1hhj 4#fh #a1gbb 4#ii #bad 4#ef #d by #aa #ahj #a #ah4d #bc4i #c1jgh 4#df #h1jjj 4#fi #a1ffj 4#ie #bea 4#ff #f by #h #agg #f #bj4j #ac4g #d1bbg 4#fc #h1aif 4#ga #a1fcd 4#id #agg 4#df #b by #b #cj #ag #ae4i #ac4i #f1gej #a4jj #aa1ebj #a4jj #a1gdj #a4jj #chc #a4jj ,douglas fir #h by #af #ahj #ia #bj4h #ac4a #d1efc 4#fh #f1cgb 4#fa #a1edi 4#ia #bfi 4#fd #e by #h #ahj #cj #ad4i #ab4b #e1jfe 4#gf #f1ggg 4#fe #a1hec #a4ji #bah 4#eb #b by #b #bd #baa #ai4j #af4d #f1fhf #a4jj #aj1cgh #a4jj #a1fie #a4jj #dai #a4jj ,shortleaf pine #h by #af #ahj #c #ag4j #ab4c #d1bbj 4#ed #f1jcj 4#ej #a1eag 4#he #cih 4#ih #h by #ad #ahj #c #af4j #ab4c #d1bec 4#ee #e1cdg 4#dd #a1geg 4#ih #cjg 4#gf #h by #ab #ahj #g #af4j #ab4d #e1jea 4#fe #g1cca 4#fj #a1hjc #a4ja #cfa 4#hi #e by #h #ahj #f #ab4b #bb4e #g1abc 4#ib #i1cgc 4#gg #a1ihe #a4aa #cja 4#gd #b by #b #cj #fg #ad4b #ac4g #g1ghj #a4jj #ab1abj #a4jj #a1gib #a4jj #djd #a4jj ,western larch #h by #af #ahj #bc #ah4c #ba4i #c1cdc 4#eg #e1ddj 4#ec #a1dji 4#ij #cdi 4#if #h by #ab #ahj #bi #ag4h #bc4d #c1fca 4#fb #f1ahf 4#fj #a1edi 4#ii #bie 4#ha #e by #h #ahj #aj #ac4f #bg4f #d1gcj 4#hj #g1beh 4#ga #a1fbj #a4jd #bba 4#fa #b by #b #cj #bdj #af4a #bf4h #e1hhj #a4jj #aj1bed #a4jj #a1efd #a4jj #cfd #a4jj ,loblolly pine #h by #af #ahj #ad #bj4e #g4d #d1aie 4#ha #f1gcd 4#gb #a1fai #a4aj #dfb #a4de #f by #af #abf #d #bj4b #e4j #b1dcb 4#dg #d1bie 4#df #a1cbd 4#ij #bff 4#hd #f by #aj #agd #c #ba4c #d4g #c1ajj 4#fj #f1afg 4#ff #a1ddi 4#ii #agc 4#ed #d by #ab #agd #d #ai4h #d4g #b1gac 4#eb #e1gde 4#fa #a1bdi 4#he #ahe 4#eh #h by #h #ahj #i #bb4i #d4i #b1ijc 4#ef #d1eeg 4#dh #a1acf 4#gg #ic 4#bi #f by #g #add #b #ba4a #e4j #b1iij 4#eh #d1ifh 4#ec #a1bhf 4#hh #aaf 4#cf #d by #h #acb #h #ai4e #i4a #c1chd 4#fe #f1aid 4#ff #a1bjj 4#hb #aif 4#fb #b by #b #cj #abc #ag4f #f4f #e1agj #a4jj #i1djj #a4jj #a1dfg #a4jj #cah #a4jj ,tamarack #f by #ab #afb #e #bc4j #ae4a #c1dcd 4#de #e1fdj 4#dc #a1ccj 4#hb #cah 4#ge #d by #aj #afb #d #ad4d #i4g #d1ajj 4#ed #e1cbj 4#da #a1chf 4#hd #beb 4#ei #b by #b #cj #dg #aa4c #af4b #g1fcj #a4jj #ac1jhj #a4jj #a1fbj #a4jj #dbe #a4jj ,western hemlock #h by #af #ahj #dd #ag4g #ag4h #d1cih 4#fi #f1dbj 4#fb #a1gcg #a4jd #djf #a4jf #b by #b #bh #caa #ag4i #ai4d #f1ccc #a4jj #aj1cfi #a4jj #a1fff #a4jj #chb #a4jj ,redwood #h by #af #ahj #f #bf4c #bb4d #c1gig 4#gi #d1dbh 4#eg #a1ajg 4#if #bid #a4je #f by #ab #ahj #f #af4a #ag4g #c1age 4#ff #c1cec 4#dc #gbh 4#fd #afg 4#fj #g by #i #ahj #f #ae4i #ae4b #c1bhj 4#fi #d1jjb 4#ea #a1ajd 4#if #adg 4#ec #c by #ad #ahj #f #ac4a #bd4d #e1jcc 4#fd #bia #a4jd #b by #ab #ahj #e #ac4h #ad4d #c1ibh 4#hb #e1ccf 4#fh #a1bdi #a4ji #bfj 4#ic #b by #aj #ahj #e #ac4h #bd4h #c1geg 4#gi #d1fjf 4#ei #a1aih #a4je #ahf 4#fg #b by #h #ahj #f #ac4g #bj4g #d1cad 4#ij #e1jej 4#fe #a1cac #a4ae #aff 4#fj #b by #b #bh #abb #ae4b #ah4h #d1ggg #a4jj #g1gih #a4jj #a1adf #a4jj #bgi #a4jj ,norway pine #f by #ab #afb #e #af4g #h4a #b1ifh 4#ef #e1bjd 4#fa #a1abc 4#ig #bhf #a4jb #d by #aj #afb #e #ac4g #ab4j #e1agj 4#ih #f1ijd 4#hb #a1gab #a4dh #cag #a4ac #b by #b #cj #fj #ad4i #aa4b #e1bhj #a4jj #h1dgj #a4jj #a1aeh #a4jj #bha #a4jj ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------- ,note4--,following is an explanation of the abbreviations used in the foregoing tables3 ,f4,s4 at ,e4,l4 ,fiber stress at elastic limit4 ,m4 of ,e4 ,modulus of elasticity4 ,m4 of ,r4 ,modulus of rupture4 ,cr4 str4 at ,e4,l4 ,crushing strength at elastic limit4 ,cr4 str4 at max4 ld4 ,crushing strength at maximum load4 ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------------------- ,,table ,,xxi ,,table ,,xxi ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------------------- ,,compression ,,and ,,shear ,,tests ,,on ,,air-,,seasoned ,,material ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------------------- ,compression ,compression ,shear parallel to grain perpendicular to grain ---------------------------------------- ---------------------------------------- ---------------------------------------- --- ,cr4 ,cr4 ,cr4 ,species ,per str4 ,m4 of str4 ,per str4 ,per ,size of ,no4 cent at ,e4 at max4 ,stress ,no4 cent at max4 ,no4 cent ,shear specimen of of ,e4 ,l4 per ld414 area ,height of of ld41 of of strength tests mois- per square per tests mois- per tests mois- ture square inch square ture square ture inch inch inch ---------------------------------------- ---------------------------------------- --------- --------------------------------------- #a1jjj ,inches ,lbs4 lbs4 ,lbs4 ,inches ,inches ,lbs4 ,lbs4 ,longleaf pine #d by #e #df #bf4c #c1dhj #d1hjj #d by #e #d #bb #be4a #egb #eb #bj4b #ihd ,douglas fir #f by #f #bei #bj4c #c1bga #a1jch #d1beh #d by #h #af #dd #bj4h #gcb #dfe #bb4a #hbb #b by #b #bdg #ah4g #c1hdb #a1jhd #e1jjb #d by #h #aj #cb #ah4a #ehd #d by #d #h #ea #bj4b #fch #d by #d #f #di #bd4j #fac #d by #d #d #bi #bd4h #fjc ,shortleaf pine #f by #f #bi #ae4g #d1jgj #a1iea #f1jcj #h by #e #af #d #ag4h #gbe #he #a1ace #b by #b #eg #ad4b #f1chj #h by #e #ad #c #af4c #geg #h by #e #ab #e #ae4a #gcj #e by #e #h #f #ac4j #iah #b by #b #b #eg #ac4i #ibf ,western larch #f by #f #aab #af4j #e1dde #h by #f #af #ag #ah4h #dia #aic #ae4j #ije #d by #d #ha #ad4g #f1afa #h by #f #ab #ah #ag4f #ebf #b by #b #bgj #ad4h #e1icd #e by #d #h #bb #ac4c #gce ,loblolly pine #f by #f #bc #c1ceg #a1fic #e1jje #h by #e #af #ab #ai4h #fjb #aef #aa4c #a1aae #e by #e #aj #bb4d #b1bag #ede #b1iej #h by #e #h #g #bb4i #fgi #d by #h #h #ai4d #c1jaj #fcc #c1ibj #d by #e #h #h #ai4e #gae #b by #b #fi #e1edg ,tamarack #f by #g #c #ae4g #b1beg #a1jdb #c1cbc #b by #b #b #eg #af4b #fig #fj #ad4j #hgi #d by #g #c #ac4f #c1ghj #a1cja #d1hbc #d by #d #eg #ad4i #c1chf #a1cec #d1cdf #b by #b #ff #ad4f #d1gij ,western hemlock #f by #f #ajb #ah4f #d1hdj #b1adj #e1had #g by #f #ae #be #ah4b #ead #aca #ag4g #ibd #b by #b #dfc #ag4j #d1efj #a1ibc #e1djc #f by #f #f #bf #af4h #dca #d by #d #d #f #ae4i #dhh ,redwood #f by #f #ah #af4i #d1bgf #h by #f #af #e #be4d #edh #ie #ab4d #fga #b by #b #aae #ad4f #e1aai #f by #f #ab #f #ad4g #faj #g by #f #i #e #ad4h #ejj #c by #f #ad #b #ab4f #dgj #b by #f #ab #b #af4b #dih #b by #f #aj #d #ad4c #eaa #b by #f #h #b #ac4b #dbi #b by #b #b #ade #ac4h #efd ,norway pine #f by #g #d #ae4b #b1fgj #a1ahb #d1bab #b by #b #b #cf #aj4j #ibd #dd #aa4i #a1ade #d by #g #b #bb4b #c1bge #a1gbd #d1ege #d by #d #ee #af4f #c1jdh #a1cfg #d1bag #b by #b #dd #aa4b #g1eej ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------------------- ,note4--,following is an explanation of the abbreviations used in the foregoing tables3 ,f4,s4 at ,e4,l4 ,fiber stress at elastic limit4 ,m4 of ,e4 ,modulus of elasticity4 ,m4 of ,r4 ,modulus of rupture4 ,cr4 str4 at ,e4,l4 ,crushing strength at elastic limit4 ,cr4 str4 at max4 ld4 ,crushing strength at maximum load4 ---------------------------------------- ---------------------------------------- ---------------------------------------- ----------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ------------------ ,,table ,,xxii ,,table ,,xxii ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ------------------ b,,working ,,unit-,,stresses ,,for ,,structural ,,timberc ,,expressed ,,in ,,pounds ,,per ,,square ,,inch 7,from ,manual of the ,american ,railway ,engineering ,assn41 #aiaa1 p4 #aec7 ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ------------------ ,,note4--,the working unit-stresses given in the table are intended for railroad bridges and trestles4 ,for highway bridges and trestles the unit-stresses may be increased twenty-five 7#be7 per cent4 ,for buildings and similar structures1 in which the timber is protected from the weather and practically free from impact1 the unit-stresses may be increased fifty 7#ej7 per cent4 ,to compute the deflection of a beam under long-continued loading instead of that when the load is first applied1 only fifty 7#ej7 per cent of the corresponding modulus of elasticity given in the table is to be employed4 ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ------------------ ,,bending ,,shearing ,,compression ---------------------------------------- ---------------------------------------- ---------------------------------------- --------------------------- ,ratio ,extreme ,modulus of ,parallel to ,longitudinal ,perpendicular ,parallel to ,for ,formul for of fibre elasticity the grain shear in to the grain the grain columns working stress in length ,,kind ,,of stress beams under #ae long columns over of ,,timber ---------------------------------------- ---------------------------------------- -------------------------------- diameters #ae diameters stringer ,average ,working ,average ,working ,elastic ,working ,elastic ,working ,average ,working working to ultimate stress ,average ultimate stress limit stress limit stress ultimate stress stress depth ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ---- ,douglas fir #fajj #abjj #a1eaj1jjj #fij #agj #bgj #aaj #fcj #caj #cfjj #abjj #ijj #abjj7a-l_/#fj;d7 #aj ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ---- ,longleaf pine #fejj #acjj #a1faj1jjj #gbj #ahj #cjj #abj #ebj #bfj #chjj #acjj #ihj #acjj7a-l_/#fj;d7 #aj ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ---- ,shortleaf pine #efjj #aajj #a1dhj1jjj #gaj #agj #ccj #acj #cdj #agj #cdjj #aajj #hcj #aajj7a-l_/#fj;d7 #aj ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ---- ,white pine #ddjj #ijj #a1acj1jjj #djj #ajj #ahj #gj #bij #aej #cjjj #ajjj #gej #ajjj7a-l_/#fj;d7 #aj ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ---- ,spruce #dhjj #ajjj #a1caj1jjj #fjj #aej #agj #gj #cgj #ahj #cbjj #aajj #hcj #aajj7a-l_/#fj;d7 ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ---- ,norway pine #dbjj #hjj #a1aij1jjj #eij;d #acj #bej #ajj #aej #bfjj;d #hjj #fjj #hjj7a-l_/#fj;d7 ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ---- ,tamarack #dfjj #ijj #a1bbj1jjj #fgj #agj #bfj #ajj #bbj #cbjj;d #ajjj #gej #ajjj7a-l_/#fj;d7 ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ---- ,western hemlock #ehjj #aajj #a1dhj1jjj #fcj #afj #bgj;d #ajj #ddj #bbj #cejj #abjj #ijj #abjj7a-l_/#fj;d7 ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ---- ,redwood #ejjj #ijj #hjj1jjj #cjj #hj #djj #aej #ccjj #ijj #fhj #ijj7a-l_/#fj;d7 ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ---- ,bald cypress #dhjj #ijj #a1aej1jjj #ejj #abj #cdj #agj #cijj #aajj #hcj #aajj7a-l_/#fj;d7 ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ---- ,red cedar #dbjj #hjj #hjj1jjj #dgj #bcj #bhjj #ijj #fhj #ijj7a-l_/#fj;d7 ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ---- ,white oak #egjj #aajj #a1aej1jjj #hdj #baj #bgj #aaj #ibj #dej #cejj #acjj #ihj #acjj7a-l_/#fj;d7 #ab ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ------------------ ,these unit-stresses are for a green condition of timber and are l ,length in inches4 to be used without increasing the live load stresses for impact4 d ,least side in inches4 ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ------------------ ,footnote b3 ,adopted1 ,vol4 #aiji1 pp4 #ecg1 #efd1 #fji-faa4 ,footnote c3 ,green timber in exposed work4 ,footnote d3 ,partially air-dry ---------------------------------------- ---------------------------------------- ---------------------------------------- ---------------------------------------- ------------------ ,,bibliography ,part ,i3 ,some general works on mechanics1 materials of construction1 and testing of materials4 ,part ,,ii3 ,publications and articles on the mechanical properties of wood1 and timber testing4 ,part ,,iii3 ,publications of the ,u4,s4 ,government on the mechanical properties of wood1 and timber testing4 ,,part #a4 ,,some ,,general ,,works ,,on ,,mechanics1 ,,materials ,,of ,,construction1 ,,and ,,testing ,,of ,,materials ,,allan1 ,,william3 ,strength of beams under transverse loads4 ,new ,york1 #ahic4 ,,anderson1 ,,sir ,,john3 ,the strength of materials and structures4 ,london1 #aijb4 ,,barlow1 ,,peter3 ,strength of materials1 #ast ed4 #ahag2 rev4 #ahfg4 ,,burr1 ,,william ,h43 ,the elasticity and resistance of the materials of engineering4 ,new ,york1 #aiaa4 ,,church1 ,,irving ,p43 ,mechanics of engineering4 ,new ,york1 #aiaa4 ,,hatfield1 ,r4,g43 ,theory of transverse strain4 #ahgg4 ,,hatt1 ,w4,k41 and ,,scofield1 ,h4,h43 ,laboratory manual of testing materials4 ,new ,york1 #aiac4 ,,jameson1 ,j4,m43 ,exercises in mechanics4 7,wiley technical series47 ,new ,york1 #aiac4 ,,jamieson1 ,,andrew3 ,strength of materials4 7,applied mechanics and mechanical engineering1 ,vol4 ,,ii47 ,london1 #aiaa4 ,,johnson1 ,j4,b43 ,the materials of construction4 ,new ,york1 #aiaj4 ,,kent1 ,,william3 ,the strength of materials4 ,new ,york1 #ahij4 ,,kottcamp1 ,j4,p43 ,exercises for the applied mechanics laboratory4 7,wiley technical series47 ,new ,york1 #aiac4 ,,lanza1 ,,gaetano3 ,applied mechanics4 ,new ,york1 #aija4 ,,merriman1 ,,mansfield3 ,mechanics of materials4 ,new ,york1 #aiab4 ,,murdock1 ,h4,e43 ,strength of materials4 ,new ,york1 #aiaa4 ,,rankine1 ,,william ,j4,m43 ,a manual of applied mechanics4 ,london1 #aija4 ,,thil1 ,a43 ,conclusion de l'tude prsente la ,commission des mthodes d'essai des matriaux de construction4 ,paris1 #aijj4 ,,thurston1 ,,robert ,h43 ,a treatise on non-metallic materials of engineering3 stone1 timber1 fuel1 lubricants1 etc4 7,materials of engineering1 ,part ,i47 ,new ,york1 #ahii4 ,,unwin1 ,,william ,c43 ,the testing of materials of construction4 ,london1 #ahii4 ,,waterbury1 ,l4,a43 ,laboratory manual for testing materials of construction4 ,new ,york1 #aiab4 ,,wood1 ,,devolson3 ,a treatise on the resistance of materials4 ,new ,york1 #ahig4 ,,part ,,ii4 ,,publications ,,and ,,articles ,,on ,,the ,,mechanical ,,properties ,,of ,,wood1 ,,and ,,timber ,,testing ,,abbot1 ,,arthur ,v43 ,testing machines1 their history1 construction and use4 ,van ,nostrand's ,eng4 ,mag41 ,vol4 ,,xxx1 #ahhd1 pp4 #bjd-bad2 #cbe-cdd2 #chb-cig2 #dgg-dij4 ,,adams1 ,e4,e43 ,tests to determine the strength of bolted timber joints4 ,cal4 ,jour1 of ,technology1 ,sept41 #aijd4 ,,alvarez1 ,,arthur ,c43 ,the strength of long seasoned ,douglas fir and redwood4 ,univ4 of ,cal4 ,pub4 in ,eng41 ,vol4 ,i1 ,no4 #b1 ,berkeley1 #aiac1 pp4 #aa-bj4 ,,barlow1 ,,peter3 ,an essay on the strength and stress of timber4 ,london1 #ahag2 #c;d ed41 #ahbf4 ----3 ,experiments on the strength of different kinds of wood made in the carriage department1 ,royal ,arsenal1 ,woolwich4 ,jour4 ,franklin ,inst41 ,vol4 ,x1 #ahcb1 pp4 #di-eb4 ,reprinted from ,philosophical ,mag4 and ,annals of ,philos41 ,no4 #fc1 ,mch41 #ahcb4 ,,bates1 ,,onward3 ,pine stringers and floorbeams for bridges4 ,trans4 ,am4 ,soc4 ,c4,e41 ,vol4 ,,xxiii4 ,,bauschinger1 ,,johann3 ,untersuchungen ber die ,elasticitt und ,festigkeit von ,fichten- und ,kiefernbauhlzern4 ,mitt4 a4 d4 mech4-tech4 ,laboratorium d4 k4 techn4 ,hochschule in ,mnchen1 #i4 ,hft41 ,mnchen1 #ahhc4 ----3 ,verhandlungen der ,mnchener ,conferenz und der von ihr gewhlten stndigen ,commission zur ,vereinbarung einheitlicher ,prfungsmethoden fr ,bau- und ,constructions-material4 ,ibid41 #ad4 ,hft41 #ahhf4 ----3 ,untersuchungen ber die ,elasticitt und ,festigkeit verschiedener ,nadelhlzer4 ,ibid41 #af4 ,hft41 #ahhg4 ,,beare1 ,t4 ,,hudson3 ,timber3 its strength and how to test it4 ,engineering1 ,london1 ,dec4 #i1 #aijd4 ,,beauverie1 ,j43 ,le bois4 ,i4 ,paris1 #aije1 pp4 #aje-ahe4 ----3 ,les bois industriels4 ,paris1 #aiaj1 pp4 #ee-gg4 ,bending tests with wood1 executed at the ,danish ,state ,testing ,laboratory1 ,copenhagen4 ,proc4 ,int4 ,assn4 ,test4 ,mat41 #aiab1 ,,xxiii#b1 pp4 #ag4 ,see also ,eng4 ,record1 ,vol4 ,,lxvi1 #aiab1 p4 #bfi4 ,,berg1 ,,walter ,g43 ,berg's complete timber test record4 ,chicago1 #ahii4 ,reprint from ,am4 ,by4 ,bridges and ,buildings4 ,,boulger1 ,g4,s43 ,wood4 ,london1 #aijh1 pp4 #aab-aba4 ,,bouniceau1--3 ,note et expriences sur la torsion des bois4 ,n4p41 n4d4 ,,bovey1 ,,henry ,t43 ,results of experiments at ,mc,gill ,university1 ,montreal1 on the strength of ,canadian ,douglas fir1 red pine1 white pine1 and spruce4 ,trans4 ,can4 ,soc4 ,c4,e41 ,vol4 ,,ix1 ,part ,i1 #ahie1 pp4 #fi-bcf4 ,,breuil1 ,m4 ,,pierre3 ,contribution to the discussion on the testing of wood4 ,proc4 ,int4 ,assn4 ,test4 ,mat41 #aijf1 ,disc1 #a;e1 pp4 #b4 ,,brown1 ,t4,s43 ,an ,account of some experiments made by order of ,col4 ,totten1 at ,fort ,adams1 ,newport1 ,r4,i41 to ascertain the relative stiffness and strength of the following kinds of timber1 viz43 white pine 7,pinus strobus71 spruce 7,abies nigra71 and southern pine 7,pinus australis71 also called long-leaved pine4 ,jour4 ,franklin ,inst41 ,vol4 ,,vii 7n4s471 #ahca1 pp4 #bcj-bch4 ,,buchanan1 ,c4,p43 ,some tests of old timber4 ,eng4 ,news1 ,vol4 ,,lxiv1 ,no4 #bc1 #aiaj1 p4 #fg4 ,,busgen1 ,m43 ,zur ,bestimmung der ,holzhrten4 ,zeitschrift f4 ,forst- und ,jagdwesen4 ,berlin1 #aijd1 pp4 #edc-efb4 ,,chevandier1 ,e41 et ,,wertheim1 ,g43 ,mmoire sur les proprits mcaniques du bois4 ,paris1 #ahdf4 ,,cieslar1 ,a43 ,studien ber die ,qualitt rasch erwachsenen ,fichtenholzes4 ,centralblatt f4 d4 ges4 ,forstwesen1 ,wien1 #aijb1 pp4 #ccg-djc4 ,,cline1 ,mc,g,a,r,v,e,y3 ,forest ,service investigations of ,american woods with special reference to investigations of mechanical properties4 ,proc4 ,int4 ,assn4 ,test4 ,mat41 #aiab1 ,,xxiii#e1 pp4 #ag4 ----3 ,forest ,service tests to determine the influence of different methods and rates of loading on the strength and stiffness of timber4 ,proc4 ,am4 ,soc4 ,test4 ,mat41 ,vol4 ,,viii1 #aijh1 pp4 #ece-edj4 ----3 ,the ,forest ,products ,laboratory3 its purpose and work4 ,proc4 ,am4 ,soc4 ,test4 ,mat41 ,vol4 ,x1 #aiaj1 pp4 #dgg-dhi4 ----3 ,specifications and grading rules for ,douglas fir timber3 an analysis of ,forest ,service tests on structural timbers4 ,proc4 ,am4 ,soc4 ,test4 ,mat41 ,vol4 ,,xi1 #aiaa1 pp4 #gdd-gff4 ,comparative strength and resistance of various tie timbers4 ,elec4 ,traction ,weekly1 ,chicago1 ,june #ae1 #aiab4 ,,day1 ,,frank ,m43 ,microscopic examination of timber with regard to its strength4 #ahhc1 pp4 #f4 ,,dewell1 ,h4,d43 ,tests of some joints used in heavy timber framing4 ,eng4 ,news1 ,mch4 #ai1 #aiad1 pp4 #eid-eih2 et seq4 ,d,,rr1 ,,karl3 ,die ,festigkeit von ,fichten- und ,kiefernholz4 ,deutsche ,bauzeitung1 ,berlin1 ,aug4 #ag1 #aiaj4 ,see also ,zeitschrift d4 ver4 deutsch4 ,ing41 ,bd4 #ed1 ,nr4 #cf1 #aiaj1 p4 #aejc4 ,,dupin1 ,,charles3 ,expriences sur la flexibilit1 la force1 et l'lasticit des bois4 ,jour1 de l'cole ,polytechnique1 ,vol4 ,x1 #ahae4 ,,dupont1 ,,adolphe1 et ,,bouquet ,,de ,,la ,,grye3 ,les bois indignes et trangers4 ,paris1 #ahge1 pp4 #bgc-ceb4 ,,estrada1 ,,esteban ,,duque3 ,on the strength and other properties of ,cuban woods4 ,van ,nostrand's ,eng4 ,mag41 ,vol4 ,,xxix1 #ahhc1 pp4 #dag-dbf2 #ddc-ddi4 ,,everett1 ,w4,h43 ,memorandum on mechanical tests of some ,indian timbers4 ,govt4 ,bul4 ,no4 #f 7o4s471 ,calcutta4 ,,exner1 ,,wilhelm ,,franz3 ,die mechanische ,technologie des ,holzes4 ,wien1 #ahga4 7,a translation and revision of ,chevandier and ,wertheim's ,mmoire sur les proprits mcaniques du bois47 ----3 ,die technischen ,eigenschaften der ,hlzer4 ,lorey's ,handbuch der ,forstwissenschaft1 ,,ii4 ,bd41 #f4 ,kap41 ,tbingen1 #aijc4 ,,fernow1 ,b4,e43 ,scientific timber testing4 ,digest of ,physical ,tests1 ,vol4 ,i1 ,no4 #b1 #ahif1 pp4 #hg-ie4 ,,fowke1 ,,francis3 ,experiments on ,british colonial and other woods4 #ahfg4 ,,gardner1 ,,roland3 ,i4 ,mechanical tests1 properties1 and uses of thirty ,philippine woods4 ,,ii4 ,philippine sawmills1 lumber market and prices4 ,bul4 #d1 ,bu4 ,for41 ,p4,i41 #aijf4 7#b;d ed41 #aijg1 contains tests of #cd woods47 ,,gayer1 ,,karl3 ,forest utilization4 7,vol4 ,v1 ,schlich's ,manual of ,forestry4 ,translation of ,die ,forstbenutzung1 ,berlin1 #ahid47 ,london1 #aijh4 ,,gollner1 ,h43 ,ueber die ,festigkeit des ,schwarzfhrenholzes4 ,mitt4 a4 d4 forstl4 ,versuchswesen ,oesterreichs4 ,,ii4 ,bd41 #c4 ,hft41 ,wien1 #ahha4 ,,gottgetreu1 ,,rudolph3 ,physische und chemische ,beschaffenheit der ,baumaterialien4 #c;d ed41 ,berlin1 #ahhj4 ,,green1 ,a4,o43 ,tasmanian timbers3 their qualities and uses4 ,hobart1 ,tasmania1 #aijc1 pp4 #fc4 ,,gregory1 ,w4,b43 ,tests of creosoted timber4 ,trans4 ,am4 ,soc4 ,c4,e41 ,vol4 ,,lxxvi1 #aiac1 pp4 #aaib-abjc4 ,see also ibid41 ,vol4 ,,lxx1 p4 #cg4 ,,grisard1 ,,jules1 et ,,vandenberghe1 ,,maximilien3 ,les bois industriels1 indignes et exotiques2 synonymie et description des espces1 proprits physiques des bois1 qualits1 dfauts1 usages et emplois4 ,paris1 #ahi-4 ,from ,bul4 de la ,socit nationale d'acclimatation de ,france1 ,vols4 ,,xxxviii-,,xl4 ,hardwoods of ,western ,australia4 ,engineering1 ,vol4 ,,lxxxiii1 ,jan4 #aa1 #aijg1 pp4 #ce-cg4 ,,hatt1 ,,william ,,kendrick3 ,a ,preliminary program for the timber test work to be undertaken by the ,bureau of ,forestry1 ,united ,states ,department of ,agriculture4 ,proc4 ,am4 ,soc4 ,test4 ,mat41 ,vol4 ,,iii1 #aijc1 pp4 #cjh-cdc4 ,appendix ,i3 ,method of determining the effect of the rate of application of load on the strength of timber1 pp4 #cbe-cbg2 ,app4 ,,ii3 ,a discussion on the effect of moisture on strength and stiffness of timber1 together with a plan of procedure for future tests1 pp4 #cbh-ccd4 ,,hatt1 ,,william ,,kendrick3 ,relation of timber tests to forest products4 ,proc4 ,int4 ,assn4 ,test4 ,mat41 #aijf1 ,c #b e1 pp4 #f4 ----3 ,structural timber4 ,proc4 ,western ,ry4 ,club1 ,st4 ,louis1 ,mch4 #ag1 #aijh4 ----3 ,abstract of report on the present status of timber tests in the ,forest ,service1 ,united ,states ,department of ,agriculture4 ,proc4 ,int4 ,assn4 ,test4 ,mat41 #aiji1 ,,xvl1 pp4 #aj4 ---- and ,,turner1 ,w4,p43 ,the ,purdue ,university impact machine4 ,proc4 ,am4 ,soc4 ,test4 ,mat41 ,vol4 ,,vi1 #aijf1 pp4 #dfb-dge4 ,,haupt1 ,,herman3 formul for the strain upon timber4 ,center of gravity of an ungula and semi-cylinder4 ,jour4 ,franklin ,inst41 ,vol4 ,,xix1 #c;d series1 #ahej1 pp4 #djh-dac4 ,,hearding1 ,w4,h43 ,report upon experiments 444 upon the compressive power of pine and hemlock timber4 ,washington1 #ahgb1 pp4 #ab4 ,,howe1 ,,malverd ,a43 ,wood in compression2 bearing values for inclined cuts4 ,eng4 ,news1 ,vol4 ,,lxviii1 #aiab1 pp4 #aij-aia4 ,,hoyer1 ,,egbert3 ,lehrbuch der vergleichenden mechanischen ,technologie4 #ahgh4 ,,ihlseng1 ,,mangus ,c43 ,on the modulus of elasticity of some ,american woods as determined by vibration4 ,van ,nostrand's ,eng4 ,mag41 ,vol4 ,,xix1 #ahgh1 pp4 #h-i4 ----3 ,on a mode of measuring the velocity of sounds in woods4 ,am4 ,jour4 ,sci4 and ,arts1 ,vol4 ,,xvii1 #ahgi4 ,,jaccard1 ,p43 tude anatomique des bois comprims4 ,mitt4 d4 ,schw4 ,centralanstalt f4 d4 forst4 ,versuchswesen4 ,x4 ,bd41 #a4 ,hft41 ,zurich1 #aiaj1 pp4 #ec-aja4 ,,janka1 ,,gabriel3 ,untersuchungen ber die ,elasticitt und ,festigkeit der sterreichischen ,bauhlzer4 ,i4 ,fichte ,sdtirols2 ,,ii4 ,fichte von ,nordtirol vom ,wienerwalde und ,erzgebirge2 ,,iii4 ,fichte aus den ,karpaten1 aus dem ,bhmerwalde1 ,ternovanerwalde und den ,zentralalpen4 ,technische ,qualitt des ,fichtenholzes im allgemeinen2 ,,iv4 ,lrche aus dem ,wienerwalde1 aus ,schlesien1 ,nord- und ,sdtirol4 ,mitt4 a4 d4 forst4 ,untersuchungswesen ,oesterreichs1 ,wien1 #aijj-ac4 ----3 ,untersuchungen ber ,holzqualitt4 ,centralblatt f4 d4 ges4 ,forstwesen4 ,wien1 #aijd1 pp4 #ie-aae4 ----3 ,ueber neuere holztechnologische ,untersuchungen4 ,oesterr4 ,vierteljahresschrift fr ,forstwesen1 ,wien1 #aijf1 pp4 #bdh-bfi4 ----3 ,die ,hrte des ,holzes4 ,centralblatt f4 d4 ges4 ,forstwesen1 ,wien1 #aijf1 pp4 #aic-bjb2 #bda-bfj4 ,,janka1 ,,gabriel3 ,die ,einwirkung von ,sss- und ,salzwssern auf die gewerblichen ,eigenschaften der ,hauptholzarten4 ,i4 ,teil4 ,untersuchungen u4 ,ergebnisse in mechanisch-technischer ,hinsicht4 ,mitt4 a4 d4 forst4 ,versuchswesen ,oesterreichs1 #cc4 ,hft41 ,wien1 #aijg4 ----3 ,results of trials with timber carried out at the ,austrian forestry testing-station at ,mariabrunn4 ,proc4 ,int4 ,assn4 ,test4 ,mat41 #aijf1 ,disc4 #b e1 pp4 #g4 ----3 ,ueber die an der k4 k4 forstlichen ,versuchsanstalt ,mariabrunnen gewonnenen ,resultate der ,holzfestigkeitsprfungen4 ,zeitschrift d4 ,oesterr4 ,ing4 u4 ,arch4 ,ver41 ,wien1 ,aug4 #i1 #aijg4 ----3 ,ueber ,holzhrteprufng4 ,centralblatt f4 d4 ges4 ,forstwesen1 ,wien1 #aijh1 pp4 #ddc-def4 ----3 ,testing the hardness of wood by means of the ball test4 ,proc4 ,int4 ,assn4 ,test4 ,mat41 #aiab1 ,,xxiii#c4 ,,jenny1 ,k43 ,untersuchungen ber die ,festigkeit der ,hlzer aus den ,lndern der ungarischen ,krone4 ,budapest1 #ahgc4 ,,johnson1 ,j4,b43 ,time tests of timber in endwise compression4 ,paper before ,section ,d1 ,am4 ,assn4 for ,adv4 of ,sci41 ,aug41 #ahih4 ,,johnson1 ,,walter ,b43 ,experiments on the adhesion of iron spikes of various forms when driven into different species of timbers4 ,jour4 ,franklin ,inst41 ,vol4 ,,xix 7n4s471 #ahcg1 pp4 #bha-bib4 ,,julius1 ,g4,a43 ,western ,australia timber tests1 #aijf4 ,the physical characteristics of the hardwoods of ,western ,australia4 ,perth1 #aijf1 pp4 #cf4 ----3 ,supplement to the ,western ,australia timber tests1 #aijf4 ,the hardwoods of ,australia4 ,perth1 #aijg1 pp4 #f4 ,,karmarsh1 ,,carl3 ,handbuch der mechanischen ,technologie4 ,i4 ,aufl41 #ahcg2 ,v4 ,aufl41 #ahge2 verm4 von ,h4 ,fisher1 #ahhh4 ,,kidder1 ,f4,e43 ,experiments on the transverse strength of southern and white pine4 ,van ,nostrand's ,eng4 ,mag41 ,vol4 ,,xxii1 #ahhj1 pp4 #aff-afh4 ----3 ,experiments on the strength and stiffness of small spruce beams4 ,ibid41 ,vol4 ,,xxiv1 #ahha1 pp4 #dgc-dgg4 ----3 ,experiments on the fatigue of small spruce beams4 ,jour4 ,franklin ,inst41 ,vol4 ,,cxiv1 #ahhb1 pp4 #bfa-bgi4 ,,kidwell1 ,,edgar3 ,the efficiency of built-up wooden beams4 ,trans4 ,am4 ,inst4 ,min4 ,eng41 ,feb41 ,june1 #ahih4 ,,kirkaldy1 ,,wm4 ,g43 ,illustrations of ,david ,kirkaldy's system of mechanical testing4 ,london1 #ahia4 ,,kummer1 ,,frederick ,a43 ,the effects of preservative treatment on the strength of timber4 ,proc4 ,am4 ,soc4 ,test4 ,mat41 ,vol4 ,,iv1 #aijd1 pp4 #dcd-dch4 ,,labord,,re1 ,p41 and ,,anstett1 ,f43 ,contribution to the study of means for improving the strength of wood for pavements4 ,proc4 ,int4 ,assn4 ,test4 ,mat41 #aiab1 ,,xxiii#d1 pp4 #ab4 ,,lanza1 ,,gaetano3 ,an account of certain tests on the transverse strength and stiffness of large spruce beams4 ,trans4 ,am4 ,soc4 ,mech4 ,eng41 ,vol4 ,,iv1 #ahhb1 pp4 #aai-ace4 ,see also ,jour4 ,franklin ,inst41 ,vol4 ,,xcv1 #ahhc1 pp4 #ha-id4 ,,laslett1 ,t43 ,properties and characteristics of timber4 ,chatham1 #ahfg4 ----3 ,timber and timber trees1 native and foreign4 7#b;d ed4 revised and enlarged by ,h4 ,marshall ,ward47 ,london and ,new ,york1 #ahid4 ,,lea1 ,w43 ,tables of strength and deflection of timber4 ,london1 #ahfa4 ,,ledebur1 ,a43 ,die ,verarbeitung des ,holzes auf mechanischem ,wege4 #ahha4 ,,lorenz1 ,n4 ,,von3 ,analytische ,untersuchung des ,begriffes der ,holzhrte4 ,centralblatt f4 d4 ges4 ,forstwesen1 ,wien1 #aiji1 pp4 #cdh-chg4 ,,ludwig1 ,,paul3 ,die ,regelprobe4 ,ein neues ,verfahren zur ,hrtebestimmung von ,materialien4 ,berlin4 #aijh4 ,,macfarland1 ,h4,b43 ,tests of longleaf pine bridge timbers4 ,bul4 #adi1 ,am4 ,ry4 ,eng4 ,assn41 ,sept41 #aiab4 ,see also ,eng4 ,news1 ,dec4 #ab1 #aiab1 p4 #ajce4 ,mc,k,a,y1 ,,donald3 ,on the weight and strength of ,american ship-timber4 ,jour4 ,franklin ,inst41 ,vol4 ,,xxxix 7#c;d series71 #ahfj1 p4 #cbb4 ,,malette1 ,j43 ,essais des bois de construction4 ,revue ,technique1 ,apr4 #be1 #aije4 ,,mann1 ,,james3 ,australian timber3 its strength1 durability1 and identification4 ,melbourne1 #aijj4 ,,martin1 ,,clarence ,a43 ,tests on the relation between cross-bending and direct compressive strength in timber4 ,railroad ,gazette1 ,mch4 #ac1 #aijc4 ,methods of testing metals and alloys 444 ,recommended by the ,fourth ,congress of the ,international ,association for ,testing ,materials1 held at ,brussels1 ,sept4 #c-f1 #aijf4 ,london1 #aijg1 pp4 #ed4 ,methods of testing wood1 pp4 #ci-di4 ,,mikolaschek1 ,,carl3 ,untersuchungen ber die ,elasticitt und ,festigkeit der wichtigsten ,bau- und ,nutzhlzer4 ,mitt4 a4 d4 forstl4 ,versuchswesen ,oesterreiches1 ,,ii4 ,bd41 #a4 ,hft41 ,wien1 #ahgi4 ,,moeller1 ,,joseph3 ,die ,rohstoffe des ,tischler- und ,drechslergewerbes4 ,i4 ,theil3 ,das ,holz4 ,kassel1 #ahhc1 pp4 #fh-abb4 ,,molesworth1 ,g4,l43 ,graphic diagrams of strength of teak beams4 ,roorke1 #ahha4 ,,morgan1 ,j4,j43 ,bending strength of yellow pine timber4 ,eng4 ,record1 ,vol4 ,,lxvii1 #aiac1 pp4 #fjh-fji4 ,,moroto1 ,k43 ,untersuchungen ber die ,biegungselasticitt und -,festigkeit der japanischen ,bauhlzer4 ,centralblatt f4 d4 ges4 ,forstwesen1 ,wien1 #aijh1 pp4 #cdf-cee4 ,,nordlinger1 ,h43 ,die technischen ,eigenschaften der ,hlzer fr ,forst- und ,baubeamte1 ,technologen und ,gewerbetreibende4 ,stuttgart1 #ahfj4 ----3 ,druckfestigkeit des ,holzes4 #ahhb4 ----3 ,die gewerblichen ,eigenschaften der ,hlzer4 ,stuttgart1 #ahij4 ,,north1 ,a4,t43 ,the grading of timber on the strength basis4 ,address before ,western ,society of ,engineers4 ,lumber ,world ,review1 ,may #be1 #aiad1 pp4 #bg-bi4 ,,norton1 ,w4,a43 ,results of experiments on the set of bars of wood1 iron1 and steel1 after a transverse stress4 ,van ,nostrand's ,eng4 ,mag41 ,vol4 ,,xvii1 #ahgg1 pp4 #eca-ece4 ,,paccinotti ,e ,,peri3 ,investigations into the elasticity of timbers4 ,il ,cimento1 ,vol4 ,,lviii1 #ahde4 ,,palacio1 ,e43 ,tensile tests of timber4 ,la ,ingenieria1 ,buenos ,aires1 ,may #ca1 #aijc1 et seq4 ,,parent1--3 ,expriences sur la rsistance des bois de chne et de sapin4 ,mmoires de l',acadmie des ,sciences1 #agjg-jh4 ,propositions relatives l'tablissement d'un precd uniforme pour l'essai des qualits techniques des bois4 ,proc4 ,int4 ,assn4 ,test4 ,mat41 #aija1 ,annexe1 pp4 #ac-bh4 ,,rogers1 ,,charles ,g43 ,a manual of forest engineering for ,india4 ,vol4 ,i1 ,calcutta1 #aijj1 pp4 #ej-ia4 ,,rudeloff1 ,m43 ,der heutige ,stand der ,holzuntersuchungen4 ,mitt4 a4 d4 kniglichen tech4 ,versuchsanstalt1 ,berlin1 ,,iv1 #ahii4 ----3 ,principles of a standard method of testing wood4 ,proc4 ,int4 ,assn4 ,test4 ,mat41 #aijf1 #bc ,c1 pp4 #af4 ----3 ,large vs4 small test-pieces in testing wood4 ,proc4 ,int4 ,soc4 ,test4 ,mat41 #aiab1 ,,xxiii#a1 pp4 #g4 ,,sargent1 ,,charles ,,sprague3 ,woods of the ,united ,states1 with an account of their structure1 qualities1 and uses4 ,new ,york1 #ahhe4 ,,schneider1 ,a43 ,zusammengesetzte ,trger4 ,zeitschrift d4 ,oesterr4 ,ing4 u4 ,arch4 ,ver41 ,nov4 #bd2 ,dec4 #i1 #ahii4 ,,schwappach1 ,a4,f43 ,beitrge zur ,kenntniss der ,qualitt des ,rotbuchenholzes4 ,zeitschrift f4 ,forst- und ,jagdwesen1 ,berlin1 #ahid1 pp4 #eac-eci4 ----3 ,untersuchungen ber ,raumgewicht und ,druckfestigkeit des ,holzes wichtiger ,waldbume4 ,berlin1 #ahig-ih4 ----3 ,etablissement de mthodes uniformes pour l'essai la compression des bois4 ,proc4 ,int4 ,assn4 ,test4 ,mat41 #aija1 ,rapport #bc1 pp4 #bh4 ,,sebert1 ,h43 ,notice sur les bois de la ,nouvelle ,caldonie suivie de considerations gnerates sur les proprits mcaniques des bois et sur les precds employs pour les mesurer4 ,paris4 ,,sherman1 ,,edward ,c43 ,crushing tests on water-soaked timbers4 ,eng4 ,news1 ,vol4 ,,lxii1 #aiji1 p4 #bb4 ,,snow1 ,,charles ,h43 ,the principal species of wood3 their characteristic properties4 ,new ,york1 #aijh4 ,,stauffer1 ,,ottmar3 ,untersuchungen ber specifisches ,trockengewicht1 sowie anatomisches ,verhalten des ,holzes der ,birke4 ,mnchen1 #ahib4 ,,stens1 ,d43 ,ueber die ,eigenschaftenimprgnierter ,grubenholzer1 insbesondere ber ihre ,festigkeit4 ,glckauf1 ,essen1 ,mch4 #f1 #aijg4 ,strength of wood for pavements4 ,can4 ,eng41 ,toronto1 ,sept4 #ab1 #aiab4 ,,st,,bschen-,,kischner3 ,karmarsch-,heerins technisches ,wrterbuch4 #c4 ,aufl41 #ahhf4 ,,talbot1 ,,arthur ,n43 ,tests of timber beams4 ,bul4 #da1 ,eng4 ,exp4 ,sta41 ,univ4 of ,ill41 ,urbana1 #aiaj4 ,tests of wooden beams made at the ,massachusetts ,institute of ,technology on spruce1 white pine1 yellow pine1 and oak beams of commercial sizes4 ,technology ,quarterly1 ,boston1 ,vol4 ,,vii1 #ahid4 ,,tetmajer1 ,l4 v43 ,zur ,frage der ,knickungsfestigkeit der ,bauhlzer4 ,schweizerische ,bauzeitung1 ,bd4 #aa1 ,nr4 #ag4 ----3 ,methoden und ,resultate der ,prfung der schweizerischen ,bauhlzer4 ,mitt4 d4 ,anstalt z4 ,prfung v4 ,baumaterialien am eidgenssischen ,polytechnicum in ,zrich4 #b4 ,hft41 #ahhd4 ----3 ,methoden und ,resultate der ,prfung der schweizerischen ,bauhlzer4 ,mitt4 d4 ,materialprfungs-,anstalt am ,schweiz4 ,polytechnikum in ,zrich4 ,landesaustellungs-,ausgabe1 #b4 ,hft41 ,zrich1 #ahif4 ,,thelen1 ,,rolf3 ,the structural timbers of the ,pacific ,coast4 ,proc4 ,am4 ,soc4 ,test4 ,mat41 ,vol4 ,,viii1 #aijh1 pp4 #eeh-efg4 ,,thurston1 ,r4,h43 ,torsional resistance of materials determined by a new apparatus with automatic registry4 ,jour4 ,franklin ,inst41 ,vol4 ,,lxv1 #ahgc1 pp4 #bed-bfj4 ----3 ,on the strength of ,american timber4 ,ibid41 ,vol4 ,,lxxviii1 #ahgi1 pp4 #bag-bce4 ----3 ,experiments on the strength of yellow pine4 ,ibid41 ,vol4 ,,lxxix1 #ahhj1 pp4 #aeg-afc4 ----3 ,influence of time on bending strength and elasticity4 ,proc4 ,am4 ,assn4 for ,adv4 ,sci41 #ahha4 ,also ,proc4 ,inst4 ,c4,e41 ,vol4 ,,lxxi4 ----3 ,on the effect of prolonged stress upon the strength and elasticity of pine timber4 ,jour4 ,franklin ,inst41 ,vol4 ,,lxxx1 #ahha1 pp4 #afa-afi4 ,,thurston1 ,r4,h43 ,on ,flint's investigations of ,nicaraguan woods4 ,ibid41 ,vol4 ,,xciv1 #ahhg1 pp4 #bhi-cae4 ,,tiemann1 ,,harry ,,donald3 ,the effect of moisture and other extrinsic factors upon the strength of wood4 ,proc4 ,am4 ,soc4 ,test4 ,mat41 ,vol4 ,,vii1 #aijg1 pp4 #ehb-eid4 ----3 ,the effect of the speed of testing upon the strength of wood and the standardization of tests for speed4 ,ibid41 ,vol4 ,,viii1 #aijh1 pp4 #eda-eeg4 ----3 ,the theory of impact and its application to testing materials4 ,jour4 ,franklin ,inst41 ,vol4 ,,clxviii1 #aiji1 pp4 #bce-bei2 #ccf-cfd4 ----3 ,some results of dead load bending tests of timber by means of a recording deflectometer4 ,proc4 ,am4 ,soc4 ,test4 ,mat41 ,vol4 ,,ix1 #aiji1 pp4 #ecd-edh4 ,,tjaden1 ,m4,e4,h43 ,het ,indrukken van ,paalkoppen in ,kespen4 ,de ,ingenieur1 ,sept4 #aa1 #aiji4 ----3 ,weerstand van ,hout loodrecht op de ,vezelrichting4 ,ibid41 ,may1 #aiaa4 ----3 ,buigvastheid van ,hout4 ,ibid41 ,may #ca1 #aiac4 ,,trautwine1 ,,john ,c43 ,shearing strength of some ,american woods4 ,jour4 ,franklin ,inst41 ,vol4 ,,cix1 #ahhj1 pp4 #aje-ajf4 ,,tredgold1 ,,thomas3 ,elementary principles of carpentry4 ,london1 #ahgj4 ,,turnbull1 ,w43 ,a practical treatise on the strength and stiffness of timber4 ,london1 #ahcc4 ,untersuchungen ber den ,einfluss des ,blauwerdens auf die ,festigkeit von ,kiefernholz4 ,mitt4 a4 d4 knig4 techn4 ,versuchsanstalten1 ,i1 #ahig4 ,verfahren zur ,prfung v4 ,metallen und ,legierungen1 von hydraulischen ,bindemitteln1 von ,holz1 von ,ton-1 ,steinzeug- und ,zementrhren4 ,empfohlen v4 dem in ,brssel v4 #c-f1 ,,ix1 #aijf1 abgeh4 ,,iv4 ,kongress des internationalen ,verbandes f4 die ,materialprfungen der ,technik4 ,wien1 #aijg4 ,,warren1 ,w4,h43 ,australian timbers4 ,sydney1 #ahib4 ----3 ,the strength1 elasticity1 and other properties of ,new ,south ,wales hardwood timbers4 ,sydney1 #aiaa4 ----3 ,the strength1 elasticity1 and other properties of ,new ,south ,wales hardwood timbers4 ,proc4 ,int4 ,assn4 ,test4 ,mat41 #aiab1 ,,xxiii#f1 pp4 #i4 ----3 ,the properties of ,new ,south ,wales hardwood timbers4 ,builder1 ,london1 ,nov4 #a1 #aiab4 ----3 ,the hardwood timbers of ,new ,south ,wales1 ,australia4 ,jour4 ,soc4 of ,arts1 ,london1 ,dec4 #f1 #aiab4 ,,wellington1 ,a4,m43 ,experiments on impregnated timber4 ,railroad ,gazette1 #ahhj4 ,,wijkander1 ----3 ,untersuchung der ,festigkeitseigenschaften schwedischer ,holzarten in der ,materialprfungsanstalt des ,chalmers'schen ,institutes ausgefhrt4 #ahig4 ,,wing1 ,,charles ,b43 ,transverse strength of the ,douglas fir4 ,eng4 ,news1 ,vol4 ,,xxxiii1 ,mch4 #ad1 #ahie4 ,,part ,,iii4 ,,publications ,,of ,,the ,u4,s4 ,,government ,,on ,,the ,,mechanical ,,properties ,,of ,,wood1 ,,and ,,timber ,,testing ,,miscellaneous ,house ,misc4 ,doc4 #db1 pt4 #i1 #dgth ,cong41 #b;d sess41 #ahhd4 7,vol4 ,,ix1 ,tenth ,census report47 ,report on the forests of ,north ,america 7exclusive of ,mexico74 ,part ,,ii1 ,the ,woods of the ,united ,states4 ,house ,report ,no4 #addb1 #ec;d ,cong41 #b;d sess4 ,investigations and tests of ,american timber4 #ahid1 pp4 #d4 ,war ,dept4 ,doc4 #a4 ,resolutions of the conventions held at ,munich1 ,dresden1 ,berlin1 and ,vienna1 for the purpose of adopting uniform methods for testing construction materials with regard to their mechanical properties4 ,by ,j4 ,bauschinger4 ,translated by ,o4,m4 ,carter and ,e4,a4 ,gieseler4 #ahif1 pp4 #dd4 ,war ,dept4 ,doc4 #aa4 ,on tests of construction materials4 ,translations from the ,french and from the ,german4 ,by ,o4,m4 ,carter and ,e4,a4 ,gieseler4 #ahif1 pp4 #hd4 ,house ,doc4 ,no4 #aha1 #eeth ,cong41 #c;d sess4 ,report upon the forestry investigations of the ,u4,s4 ,department of ,agriculture1 #ahgg-ahih4 ,by ,b4,e4 ,fernow1 #ahii1 pp4 #dja4 ,contains chapter on ,the work in timber physics in the ,division of ,forestry1 by ,filibert ,roth1 pp4 #ccj-cie4 ,,forest ,,service ,cir4 #g--,the ,government timber tests #ahi-1 pp4 #d4 ,cir4 #h--,strength of boxed or turpentine timber4 #ahib1 pp4 #d4 ,bul4 #f--,timber ,physics4 ,pt4 ,i4 ,preliminary report4 #a4 ,need of the investigation4 #b4 ,scope and historical development of the science of timber physics4 #c4 ,organization and methods of timber examinations in the ,division of ,forestry4 ,by ,b4,e4 ,fernow1 #ahib1 pp4 #eg4 ,unnumbered ,cir4--,instructions for the collection of test pieces of pines for timber investigations #ahic1 pp4 #d4 ,cir4 #i--;,effect of turpentine gathering on the timber of longleaf pine4 ,by ,b4,e4 ,fernow #ahic1 p4 #a4 ,bul4 #h--,timber physics4 ,pt4 ,,ii4 ,progress report4 ,results of investigations on longleaf pine4 #ahic1 pp4 #ib4 ,bul4 #aj--,timber3 an elementary discussion of the characteristics and properties of wood4 ,by ,filibert ,roth4 #ahie1 pp4 #hh4 ,bul4 #ab--;,economical designing of timber trestle bridges4 ,by ,a4,l4 ,johnson1 #ahif1 pp4 #eg4 ,cir4 #ab--,southern pine1 mechanical and physical properties4 #ahif1 pp4 #ab4 ,cir4 #ae--,summary of mechanical tests on thirty-two species of ,american woods4 #ahig1 pp4 #ab4 ,cir4 #ah--,progress in timber physics4 #ahih1 pp4 #bj4 ,cir4 #ai--,progress in timber physics3 ,bald cypress 7,taxodium distichum74 ,by ,filibert ,roth1 #ahih1 pp4 #bd4 ,y4,b4 ,extr4 #bhh--,tests on the physical properties of woods4 ,by ,f4,e4 ,olmstead1 #aijb1 pp4 #ecc-ech4 ,unnumbered ,cir4--,timber tests4 #aijc1 pp4 #ae4 ,unnumbered ,cir4--,timber preservation and timber testing at the ,louisiana ,purchase ,exposition4 #aijd1 pp4 #f4 ,cir4 #cb--,progress report on the strength of structural timber4 ,by ,w4,k4 ,hatt1 #aijd1 pp4 #bh4 ,bul4 #eh--,the red gum4 ,by ,alfred ,chittenden4 ,includes a discussion of ,the mechanical properties of red gum wood1 by ,w4,k4 ,hatt4 #aije1 pp4 #ef4 ,cir4 #ch--;,instructions to engineers of timber tests4 ,by ,w4,k4 ,hatt1 #aijf1 pp4 #ee4 ,revised edition1 #aiji1 pp4 #ef4 ,cir4 #ci--;,experiments on the strength of treated timber4 ,by ,w4,k4 ,hatt1 #aijf1 pp4 #ca4 ,revised edition1 #aijh4 ,bul4 #gj--;,effect of moisture upon the strength and stiffness of wood4 ,by ,h4,d4 ,tiemann1 #aijf1 pp4 #add4 ,cir4 #df--;,holding force of railroad spikes in wooden ties4 ,by ,w4,k4 ,hatt1 #aijf1 pp4 #g4 ,cir4 #dg--,strength of packing boxes of various woods4 ,by ,w4,k4 ,hatt1 #aijf1 pp4 #g4 ,cir4 #ajh--,the strength of wood as influenced by moisture4 ,by ,h4,d4 ,tiemann1 #aijg1 pp4 #db4 ,cir4 #aae--,second progress report on the strength of structural timber4 ,by ,w4,k4 ,hatt1 #aijg1 pp4 #ci4 ,cir4 #adb--,tests of vehicle and implement woods4 ,by ,h4,b4 ,holroyd and ,h4,s4 ,betts1 #aijh1 pp4 #bi4 ,cir4 #adf--;,experiments with railway cross-ties4 ,by ,h4,b4 ,eastman1 #aijh1 pp4 #cb4 ,cir4 #agi--,utilization of ,california eucalypts4 ,by ,h4,s4 ,betts and ,c4 ,stowell ,smith1 #aiaj1 pp4 #cj4 ,bul4 #ge--;,california tanbark oak4 ,part ,,ii1 ,utilization of the wood of tanbark oak1 by ,h4,s4 ,betts1 #aiaa1 pp4 #bd-cb4 ,bul4 #hh--,properties and uses of ,douglas fir4 ,by ,mc,garvey ,cline and ,j4,b4 ,knapp1 #aiaa1 pp4 #ge4 ,cir4 #ahi--,strength values for structural timbers4 ,by ,mc,garvey ,cline1 #aiab1 pp4 #h4 ,cir4 #aic--,mechanical properties of redwood4 ,by ,a4,l4 ,heim1 #aiab1 pp4 #cb4 ,bul4 #ajh--,tests of structural timbers4 ,by ,mc,garvey ,cline and ,a4,l4 ,heim1 #aiab1 pp4 #abca4 ,bul4 #aab--;,fire-killed ,douglas fir3 a study of its rate of deterioration1 usability1 and strength4 ,by ,j4,b4 ,knapp1 #aiab1 pp4 #ah4 ,bul4 #aae--,mechanical properties of western hemlock4 ,by ,o4,p4,m4 ,goss1 #aiac1 pp4 #de4 ,bul4 #abb--,mechanical properties of western larch4 ,by ,o4,p4,m4 ,goss1 #aiac1 pp4 #de4 ,cir4 #bac--,mechanical properties of woods grown in the ,united ,states4 #aiac1 pp4 #d4 ,cir4 #bad--,tests of packing boxes of various forms4 ,by ,john ,a4 ,newlin1 #aiac1 pp4 #bc4 ,review ,forest ,service ,investigations4 #aiac4 ,outline of investigations4 ,vol4 ,i1 pp4 #ag-ba4 ,a microscopic study of the mechanical failure of wood1 by ,warren ,d4 ,brush4 ,vol4 ,,ii1 pp4 #cc-ch4 ,bul4 #fg1 ,u4,s4,d4,a4--,tests of ,rocky ,mountain woods for telephone poles4 ,by ,norman de,w4 ,betts and ,a4,l4 ,heim1 #aiad1 pp4 #bh4 ,bul4 #gg1 ,u4,s4,d4,a4--,rocky ,mountain mine timbers4 ,by ,norman de,w4 ,betts1 #aiad1 pp4 #cd4 ,bul4 #hf1 ,u4,s4,d4,a4--,tests of wooden barrels4 ,by ,j4,a4 ,newlin1 #aiad1 pp4 #ab4 ,,reports ,,of ,,tests ,,on ,,the ,,strength ,,of ,,structural ,,material1 ,,made ,,at ,,the ,,watertown ,,arsenal1 ,,mass4 ,house ,ex4 ,doc4 ,no4 #ab1 #dgth ,cong41 #ast sess41 #ahhb4 ,strength of wood grown on the ,pacific slope1 pp4 #ai-ic4 ,senate ,ex4 ,doc4 ,no4 #a1 #dgth ,cong41 #b;d sess41 #ahhc4 ,resistance of white and yellow pines to forces of compression in the direction of the fibers1 as used for columns1 or posts1 pp4 #bci-cie4 ,senate ,ex4 ,doc4 ,no4 #e1 #dhth ,cong41 #ast sess41 #ahhd4 ,tests of ,california laurel wood by compression1 indentation1 shearing1 transverse tension1 pp4 #bbc-bcf4 ,tests of ,north ,american woods 7under supervision of ,prof4 ,c4,s4 ,sargent in charge of the forestry division of the ,tenth ,census71 with #af photographs of fractures of ,american woods1 pp4 #bcg-cdg4 ,senate ,ex4 ,doc4 ,no4 #ce1 #dith ,cong41 #ast sess41 #ahhe4 ,adhesion of nails1 spikes1 and screws in various woods4 ,experiments on the resistance of cut nails1 wire nails 7steel71 wood screws1 lag screws in white pine1 yellow pine1 chestnut1 white oak1 and laurel1 pp4 #ddh-dga4 ,house ,ex4 ,doc4 ,no4 #ad1 #east ,cong41 #ast sess41 #ahij4 ,adhesion of spikes and bolts in railroad ties1 pp4 #eie-fag4 ,house ,ex4 ,doc4 ,no4 #afa1 #eb;d ,cong41 #ast sess41 #ahib4 ,adhesion of nails in wood1 pp4 #gdd-gde4 ,house ,ex4 ,doc4 ,no4 #ib1 #ec;d ,cong41 #c;d sess41 #ahie4 ,woods--compression tests 7endwise compression71 pp4 #dga-dgf4 ,house ,doc4 ,no4 #ed1 #edth ,cong41 #ast sess41 #ahif4 ,compression tests on ,douglas fir wood1 pp4 #ecf-efc4 ,expansion and contraction of oak and pine wood1 pp4 #efg-egd4 ,house ,doc4 ,no4 #afd1 #eeth ,cong41 #b;d sess41 #ahih4 ,compression tests of timber posts1 pp4 #dje-daa4 ,new posts of yellow pine and spruce1 pp4 #dac-dej2 ,old yellow pine posts from ,boston ,fire ,brick ,co4 building1 ,no4 #cid ,federal ,st41 ,boston1 ,mass41 pp4 #dea-dgc4 ,house ,doc4 ,no4 #adc1 #eeth ,cong41 #c;d sess41 #ahii4 ,fire-proofed wood 7endwise and transverse tests71 pp4 #fgf-fha4 ,house ,doc4 ,no4 #aij1 #efth ,cong41 #b;d sess41 #aija4 ,cypress wood for ,united ,states ,engineer ,corps2 compression and transverse tests1 pp4 #aaba-aabf4 ,old white pine and red oak from roof trusses of ,old ,south ,church1 ,boston1 ,mass41 pp4 #aabg-aacj4 ,compression of rubber1 balata1 and wood buffers1 pp4 #aadi-aaeh4 ,house ,doc4 ,no4 #cce1 #egth ,cong41 #b;d sess41 #aijc4 ,douglas fir and white oak woods4 ,transverse and shearing tests2 also observations on heat conductivity of sticks over wood fires and a stick exposed to low temperature4 ,expansion crosswise the grain of wood after submersion1 pp4 #eai-efa4 ,adhesion of lag screws and bolts in wood1 pp4 #efc-egh4