Cyclic Testing of High-Capacity CLT Shear Walls

Abstract

Conventional cross-laminated timber (CLT) shear walls often use commercial hold-downs and shear brackets with small-diameter fasteners that limit their lateral capacities. By using higher capacity hold-down connections with large diameter dowels, bolts, or mixed angle screws, a CLT shear wall’s strength and stiffness can be significantly improved. This experimental study assessed the performance of CLT shear walls using high-capacity hold-down and shear key connections. A total of six full-scale, five-ply cantilever CLT shear walls were cyclically tested to evaluate their strength, stiffness, and hysteretic behavior. The specimens had three height-to-width aspect ratios (0.52, 1.3, and 3.3) and two hold-down fastener types (bolts and mixed angle screws). All six wall specimens exhibited significantly higher strength and initial stiffness when compared to previously tested conventional CLT shear walls. Four of the six specimens exhibited ductile behavior through yielding of their hold-down fasteners. However, the two long walls buckled prematurely, highlighting a possible failure mode for CLT shear walls with significant in-plane loading. A maximum system overstrength factor of 2.0 was observed for the walls with mixed angle screw hold-downs, and the overstrength values reduced with increasing aspect ratios. The three walls with bolted hold-downs were not tested to failure due to the longest wall buckling and the other two specimens reaching the test setup’s maximum allowable drifts of 4.5% and 6.0% for the 2.6 m–tall and 6.6 m–tall walls, respectively. Although post peak behavior was not reached, high local ductility demands of 14 and 21 were observed in the bolted connections. Therefore, their ultimate overstrength factors were not found, but the test results indicate an overstrength of 2.7 or greater can occur due to significant “rope effect” of the bolts and their excellent local ductility capacity.