A treatise on architecture and building construction . eans ofiron l)o]ts or plates, or both, the combined tensile strengthof all the members submitted to tension must be equal tothe combined strength of the members submitted to shear. For example, if we use a joint of the form shown in Fig. 23for a beam subjected to tensile strain, and omit the four boltsm, we must proportion the parts so that the shearing strengthof the keys r, .v, and the shearing strength of the materialbetween o and dc or between/ and /y will equal the tensilestrength of tlie section at /. For, no matter how much 9 CARPEN
A treatise on architecture and building construction . eans ofiron l)o]ts or plates, or both, the combined tensile strengthof all the members submitted to tension must be equal tothe combined strength of the members submitted to shear. For example, if we use a joint of the form shown in Fig. 23for a beam subjected to tensile strain, and omit the four boltsm, we must proportion the parts so that the shearing strengthof the keys r, .v, and the shearing strength of the materialbetween o and dc or between/ and /y will equal the tensilestrength of tlie section at /. For, no matter how much 9 CARPENTRY. 43 stronger any one of these details may be than is required ofit, the beam will not acquire additional strength thereby, asit will only be as strong as its weakest part. The importance of analyzing the conditions imder whicha beam will be strained is, therefore, very evident, and it isthe comprehension of these conditions, and the knowledge ofhow to provide for them, that enables us to select a properform of scarf joint in each particular Fig. 93. Fig. 23 shows the simplest form of a scarf timber a is cut half through its depth, on the line c c/,which is perpendicular to the adjoining face of the timber,as is also the line eg. Thetimber b is similarly ctit halfits depth on the line material between theseciits and the end of the tim-ber is then removed to theline d c\ and the two pieces aand b arc then joined in thesame manner as the splicejoints in Figs. 14 and 15, andare securely bolted. Thusfar the joint presents the same mechanical features undertension as would the joint shown in Fig. 21; but when sub-jected to compression the timbers a and b have a flat bearingon the surfaces in contact at gc d and at cf^ which, com-bined, are equal to the entire bearing surface of the end ofthe timber, each surface being the full breadth by half thedepth. The weakness of the joint under compression arises,therefore, from its tendency to bend and fail, either
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Keywords: ., bo, bookcentury1800, booksubjectarchitecture, booksubjectbuilding
