Torque loading tests on the rolling shear strength of cross-laminated timber

Abstract

In this study , torque loading tests on small shear blocks were performed to evaluate the rolling shear strength of cross-laminated timber (CLT). The CLT plates in the tests were manufactured with Mountain Pine Beetle-afflicted lumber boards and glued with polyurethane adhesive; two types of layups (five-layer and three-layer) with a clamping pressure 0.4 MPa were studied. The small block specimens were sampled from full-size CLT plates and the cross layers were processed to have an annular cross section. These specimens were tested under torque loading until brittle shear failure occurred in the middle cross layers. Based on the test results, the brittle shear failure in the specimens was evaluated by detailed finite element models to confirm the observed failure mode was rolling shear. Furthermore, a Monte Carlo simulation procedure was performed to investigate the occurrence probability of different shear failure modes in the tests considering the randomness of the rolling shear strength and longitudinal shear strength properties in the wood material. The result also suggested the probability of rolling shear failure is very high, which gives more confident proof that the specimens failed dominantly in rolling shear. It was also found that the torque loading test method yielded different rolling shear strength values compared to the previous research from short-span beam bending tests; such a difference may mainly be due to the different stressed volumes of material under different testing methods, which can be further investigated using the size effect theory in the future.