High-capacity hyperelastic hold-down for cross-laminated timber shear walls

Cross-laminated timber (CLT) continues to establish a stronger footing in the Canadian construction industry, also as an option for lateral load resisting systems, such as shear walls. Recent modifications to the Canadian Standard for Engineering Design in Wood (CSA O86- 19) allow only rocking kinematics as energy dissipative mechanics for CLT shear walls, whereby hold-down must remain elastic. These provisions necessitate the development of novel hold-down solutions. In this report, the performance of a hyper-elastic high-capacity hold-down was investigated at the component level through tests on: (1) hold-down steel rod, (2) CLT housing, and (3) hold-down assemblies with different sizes of rubber pads. The tests demonstrated that: i) the rubber hold-down can remain elastic under a rocking kinematics provided that the elastic limit of the steel rod is not exceeded; ii) failure of the rod is the subsequent desired ductile mode; iii) the CLT width influences the failure mode; iv) the shape factor influences the achievable deformation of the rubber pad; v) increasing the rubber pad thickness reduces the hold-down stiffness; and vi) increasing the rubber pad width increases the hold-down stiffness. Numerical modelling and optimization suggested that using an intermediate steel laminate between layers of rubber pads could improve its performance. Based on the results of the investigations presented herein, a capacity-design procedure for the hyper-elastic hold-downs was proposed.