Evaluating the Shear Stiffness of Asymmetric Angle-Ply Layers in Diagonal Cross-laminated Timber

Abstract The perpendicular orientation of the cross-layer (s) makes Cross-laminated Timber (CLT) susceptible to rolling shear failure and reduced stiffness in bending. Under out-of-plane bending, rolling shear failure occurs in the cross layers along the radial-tangential plane. This weakness in CLT panels could be improved by varying the grain orientation of the cross-layers away from perpendicular-to-grain (90°), and closer to parallel-to-grain (0°). This paper studies the shear stiffness of a pair of asymmetric angle-ply layers rotated at angles from 90° to 70°, 40°, 20°, 10°, and 0°. These two layers with varying grain orientations were assumed to be representative of the inner layers of a four-ply Diagonal Cross-laminated Timber (DCLT) panel. For this purpose, Hankinson’s formula was applied in addition to two-plate shear tests and numerical modeling. The experimental testing and FE model results were compared with the theoretical values to evaluate the theory for shear stiffness prediction of the asymmetric angle-ply layers. The results of the three methods showed an agreement in predicting an increase in shear stiffness when the angle-ply orientation of the layers decreases from 90° to 0°. The results indicated that Hankinson’s formula seems to be a conservative theoretical predictor for the shear stiffness of diagonal layers. Regarding the experimental results, orienting the cross layers to an angle between 70° and 40° was shown to improve the rolling shear stiffness by 10% and 46% respectively. This research provides insights into innovations towards CLT development with improved rolling shear stiffness using diagonally-oriented layers.