Shear Properties of Symmetric Angle-Ply Cross-Laminated Timber Panels

The development of cross-laminated timber (CLT) technology has revolutionized the construction industry, enabling wood into new markets and exciting large-scale applications. The traditional 90° layup of CLT, however, is rudimentary compared to most laminated composite materials (e.g., for the aerospace industry or sports equipment) and could be viewed as just the starting point for the next generation of mass timber panels. This study examines the effect of varying fiber orientation of the mid-layer of three-ply CLT on the shear properties of the panel. Short-span shear specimens were fabricated from eastern hemlock boards where the mid-layer was oriented at 30°, 45°, 60°, and 90° with respect to the panel’s major axis direction. Shear strength and deformation of the panels were measured following the three-point bending test according to ASTM D198. In addition, predictions were made using a shear analogy method and a 2D linear elastic finite element model for comparison with experimental results. The results show a general tendency for both major axis bending and shear properties to increase when changing the fiber orientation of the mid-layer from 90° to 30°. Moreover, mean values of effective shear stiffness ($G{A}_{eff}$) and shear strength ($F_v$) obtained from the CLT panel with 30° fiber orientation were 828% and 48% higher, respectively, than those for traditional 90° CLT. Finite element simulations were in good agreement with the experiments for 90° CLT; however, for angled CLT specimens, the finite element model and shear analogy method predicted higher deformation due to the biaxial shear stresses from off-axis loading and bending-twisting coupling in the mid-layer, which these stresses are not taken into account by either prediction method.