Influence of Lamination Aspect Ratios and Test Methods on Rolling Shear Strength Evaluation of Cross-Laminated Timber

Rolling shear (RS) strength may govern load-carrying capacity of cross-laminated timber (CLT) subjected to high out-of-plane loading because high RS stresses may be induced in cross layers and wood typically has low RS strength. This study investigates RS strength properties of non-edge-glued CLT via experimental testing (short-span bending tests and modified planar shear tests) and numerical modeling. CLT specimens with different manufacturing parameters including two timber species (New Zealand-grown Douglas fir and Radiata pine), three lamination thicknesses (20, 35, and 45 mm), and various lamination aspect ratios (4.1-9.8) were studied. The lamination aspect ratio was found to have a substantial impact on RS strength of CLT. Higher aspect ratios led to a significant increase of RS strength, and an approximately linear relationship could be established. With similar lamination aspect ratios, the Radiata pine CLT had higher RS strength than the Douglas fir CLT. The two different test methods, however, yielded comparable RS strength assessments. Numerical models were further developed to study the influence of the test configurations and gaps in the cross layers on stress distributions in the cross layers. It was also found that the compressive stresses perpendicular to the grain in cross layers had negligible influence on the RS strength evaluations.