Dynamic and quasi-static evaluation of stiffness properties of CLT: longitudinal MoE and effective rolling shear modulus

Cross-Laminated Timber (CLT) is an engineered wood product composed of solid layers of glued sawn timber. In this study, essential material stiffness parameters for CLT made from Norway spruce and Scots pine are evaluated. Specifically, the longitudinal modulus of elasticity (MoE) for longitudinally oriented layers and the effective rolling shear modulus for transversely oriented layers are the focus. By combining finite element (FE) analysis with four-point, out-of-plane bending tests using digital image correlation (DIC), a robust assessment of the effective rolling shear modulus of CLT layers is achieved. Additionally, eigenvalue analysis, applied to an FE model, along with resonance frequencies obtained from dynamic excitation of CLT, enables stable and simultaneous assessment of the dynamic longitudinal MoE and effective rolling shear modulus. Notably, while the dynamic MoE of longitudinal CLT layers is only 4% higher than the quasi-static local MoE, the dynamic effective rolling shear modulus of CLT layers is 40% higher than the quasi-static effective rolling shear modulus. This finding indicates a tangible viscoelastic behavior of wood concerning rolling shear.