CLT rolling shear strength: Impact of material factors and test configuration

Under flat-wise bending of cross laminated timber (CLT), the orthogonal arrangement of adjacent layers induces rolling shear (RS) stresses in planes perpendicular to grain. With the growing interest in point-supported CLT floors, where RS strength can govern the design, obtaining accurate RS strength values is critical. RS strength of CLT is assumed as one-third of the longitudinal shear (LS) strength of the CLT lamellas, e.g. in the Canadian Standard CSA O86, yet this assumption lacks experimental validation. In this study, 1028 tests were conducted on CLT samples obtained from four Canadian producers adopting different test configurations to measure RS strength. Although the obtained ratios between RS and LS strength were not exactly one-third, the current CSA O86 approach provides a reasonable estimate in the absence of test data. The characteristic RS values for E1 and V2 CLT stress grades, adjusted for standard load duration, was 0.75 MPa, 50% higher than the CSA O86 specified RS strength value of 0.5 MPa, indicating high conservatism. Higher RS strength enables the use of thinner CLT panels in shear‑governed applications, thereby improving structural economy. Therefore, for standardization purposes, it is recommended to consider revising the specified strength values. As the adopted test methods yielded similar characteristic RS strengths, considering the smaller volume used, easier specimen preparation and simpler test apparatus required, the modified planar shear test method is recommended for future test campaigns. • 1028 tests were conducted on CLT samples from four Canadian producers adopting different test methods to measure RS strength. • The current assumptions for both rolling shear and strength modulus in CSA O86 showed to be overly conservative. • Characteristic rolling‑shear strength of SPF CLT was 50% higher than the CSA O86 values for E1 and V2 grades. • Modified planar shear and bending tests yield comparable results; the small-scale method offers efficiency and convenience.