









k 



■^m GRAIN ^"- 



4 



w 







: 



















1 



" 













Figure 56. Compression parallel to grain. 





I 



X 





m — <5r4in — - m 



X 





X 



Figure 57. Compression perpendicular to grain. 



Figure 58. Shear parallel to grain. 



parallel to grain. The largest shear stress parallel to grain usually 

 occurs along the neutral axis on the plane at which the induced stress 

 changes from compression to tension and generally increases to the maximum 

 at the supports or end of the beam. Shakes, checks, and splits, which may 

 occur during the drying of lumber, have the effect of reducing the area in 

 the plane of shear resistance. Consequently, laboratory test values for 

 shear strength parallel to grain are substantially reduced for design 

 purposes in order to accommodate the probability of the occurrence of 

 shakes, checks and splits after drying. 



237 



