Experimental and numerical investigations on hysteretic response of a multi-level SMA/lead rubber bearing seismic isolation system

This study investigates the response of a shape memory alloy (SMA)-based isolation system that combines multiple groups of SMA cables and a lead rubber bearing (LRB). The isolation device, named as multi-level SMA/lead rubber bearing (ML-SLRB), is designed such that it maintains its efficiency under frequent, design and extreme levels of seismic events. Two large-size ML-SLRB isolation devices were designed and fabricated. The response of the proposed isolation systems was evaluated together with a conventional LRB under increasing amplitudes of cyclic loads. The effects of loading rate and vertical pressure on the response of the ML-SLRB isolator were evaluated. Finite element models of the fabricated ML-SLRB isolators were developed and analyzed to assess the response of the different SMA cable groups at different stages of the loading. The test results, supported by the finite element analyses, revealed that the SMA cable groups used in a loop configuration in the ML-SLRB isolator are prone to stress concentrations and early damage. The ML-SLRB isolators that employed its main SMA cable groups in a straight configuration successfully achieved a multi-level performance where the stiffness of the isolator increased as the demands of the displacement increased. The developed isolator also exhibited lower residual drifts compared to the LRB isolator.