Finite-element analysis of the stress distribution in a torsion test of full-size, structural lumber

Full-size structural lumber under torsion was analyzed using the finite-element method to determine stress distribution. A three-dimensional, homogeneous, orthotropic finite-element model was developed and analyzed using commercially available software, ANSYS®, to increase understanding of stress distribution and failure modes. Analyses revealed that uniform shear stress occurs within the shear span, which begins and ends at a distance of approximately two times the depth plus the grip distance away from each end of the specimen. In addition, finite-element analysis verified that the experimental shear-failure plane that occurs within the shear span is parallel to the grain. Shear slippage is also parallel to the grain, similar to the known shear-failure mode in specimens subjected to transverse loads. Based on results of this study, the torsion test is the best practical method to determine the pure shear strength of full-size, structural lumber.