Shear Properties of Eastern Hemlock with Respect to Fiber Orientation for Use in Cross Laminated Timber

Abstract

Shear properties of the cross layer in cross laminated timber (CLT) panels are critical for design purposes, especially for applications with high concentrated loads and low span-to-depth ratios. Understanding how the shear properties of CLT lamstock vary with respect to fiber orientation—from perpendicular-to-grain (90°) to parallel-to-grain (0°)—can lead to new and innovative panel layups with superior shear performance. In this study, two-plate shear specimens (per the relevant standard) were fabricated with fiber orientations of 0°, 30°, 45°,60°, and 90° with respect to the shear load direction using eastern hemlock 2×4 lumber. Both shear modulus and shear strength were measured as a function of fiber orientation. The influence of fiber orientation and the interaction of resisting components on the shear properties are discussed concerning observations of the types of failure modes. The results indicate that the effective shear stiffness (GAeff) and the characteristic shear strength (Fv) for a traditional (90°) CLT panel made from eastern hemlock would satisfy grade E3 CLT per the relevant standard. Moreover, the shear strength of the angled cross layers with 30° and 45° fiber orientation with respect to the major panel axis would be 98% and 59% higher, respectively, than CLT with a 90° cross layer orientation.