Development and Performance Evaluation of Multi-Stage SMA Damper-Restrained Flat Sliding Bearings for Deformation Mitigation

Seismic base isolation systems efficiently mitigate superstructural responses during earthquakes, wherein major deformations are concentrated in the isolation layer due to the flexibility of the isolation bearings. Nevertheless, isolated structures experience excessive deformations during extreme earthquakes, likely inducing unfavorable pounding behavior in the isolation layer. This study develops a multi-stage shape memory alloy (SMA) damper-restrained flat sliding bearing (GD-FSB) isolation system for deformation reduction and pounding mitigation during extreme earthquakes. The working principle of the developed isolation system is first presented, wherein gap dampers (GDs) are key components. An energy-based design procedure that considers the near-field effect was utilized for the isolation system to accommodate various deformation demands in practical engineering. Furthermore, a finite element numerical model was established to investigate the mechanical properties of GD-FSB isolators. Numerical results demonstrate that combined-SMA GDs with acceptable self-centering (SC) capacity exhibit stable damping and stiffness when clearance deformation yields, unaffecting the hysteretic behavior at small amplitudes. Subsequently, the isolation performance of structures designed with GD-FSB systems was evaluated through single-degree-of-freedom systems that considered the mainshock-aftershock sequence effect. Time history analyses reveal that, in comparison with conventional FSB systems, the GD-FSB system performs superior deformation mitigation and lower residual deformations during aftershocks and future earthquake events, preventing unexpected pounding against restraining rims. Meanwhile, in contrast with those of fully SC GDs, combined-SMA GDs achieve lower force requirements and acceleration responses to accommodate the same target deformation demand.