Elastic properties of full-size mass timber panels: Characterization using modal testing and comparison with model predictions

Mass timber panel products are leading the evolution of wood construction throughout the world. In-plane elastic properties of mass timber panels are critical in serviceability design, especially when two-dimensional mechanical behaviour is considered. In this study, the moduli of elasticity (MOE) in major and minor strength directions (Ex and Ey), and in-plane shear modulus (Gxy) of 51 industrial size cross laminated timber (CLT) panels, 4 multi-ply solid wood panels (MSWP) were measured by a modal testing method. It was found that the modal testing method was capable of characterizing the elastic constants of mass timber panels with at least 90% agreement with the results via conventional static tests. The modal test measured values were used to examine the effective stiffness prediction models of CLT and MSWP, including k-Method, Gamma Method and Shear Analogy Method. The k-Method could be used for predicting Ex and Ey values of full-size CLT and MSWP panels with a large length/width to thickness ratio. Gxy could not be well predicted by k-Method, which is greatly affected by edge bonding and gaps between laminas. The Gamma Method and Shear Analogy Method could account for the effect of transverse shear to different extents in the prediction of apparent Ex and showed close results with a large length to thickness ratio. However, the effect of transverse shear on apparent Ey could not be properly accounted for by the Shear Analogy Method for CLT panels with typical width between 1 to 3 meters.