Hyperelastic hold-down solution for CLT shear walls

Abstract

The use of cross-laminated timber (CLT) shear walls in tall buildings poses large demands on hold-downs (HD). While commonly used HDs behave as dissipative connections, the current Canadian Standard for Engineering Design in Wood recommends designing HDs as a non-dissipative connection. To satisfy this requirement, a hyperelastic elastomeric (rubber) HD was developed. Material level tests showed that the compressive behaviour of rubber layers relied on a dimensionless geometrical shape factor (SF). Component level tests on a total of 16 different HD configurations varying the width and thickness of the rubber pads were conducted under quasi-static monotonic and cyclic loading, the latter with two different loading protocols. Under monotonic loading, the rubber HDs behaved hyperelastic without any residual inelastic deformation and no damage was observed in the CLT panels or the steel parts. The HD load-displacement behaviour was mostly influenced by SF, with smaller SF leading to lower stiffness. A power function was developed to describe the load-displacement behaviour of the HD. Under cyclic loading, no strength or stiffness degradation was observed, even after multiple loading cycles. When designing CLT shear walls with the proposed hyperelastic HD, both the CLT panel as well as the steel parts must be capacity protected to prevent the brittle failure of the CLT or premature yielding of the steel.