Evaluation of the shear strength of lumber by different test methods

Four kinds of shear tests, i.e., JIS block, full-scale block, three-point bending and five-point bending, were conducted to predict the shear strength of the difficult to perform bending method from the shear strength of the easily performed block shear method. The results were as follows. The proportion of shear failure or combined shear and bending failure was very low in all species, especially in Japanese cedar, in the three-point bending method. In the five-point bending method, the rate of shear failure or combined shear and bending failure was just a little higher compared with the three-point bending method. In both Douglas fir and Hem-Fir, shear strength was about 40% higher for the lower limit in the five-point bending method than in the three-point bending method. The relational expression, which was calculated from the block shear and bending methods, agreed relatively well with the experimental value. The block shear method can therefore be used as a substitute for the more arduous bending method to predict shear strength. Also, as an example of estimation of shear strength by nondestructive tests, failure loads and failure modes in the three-point bending method were estimated by the equation calculated in this study and parameters of nondestructive measurement, and compared with measured values.