Robust optimization of SMA-FPS isolation system with uncertain parameters for response control subjected to seismic excitations

The friction pendulum system (FPS) experience large displacements at the isolation level under strong ground motions and exhibits significant residual displacements after the seismic event. To overcome these residual displacements, the shape memory alloy (SMA) can be effectively utilized in FPS isolation systems due to its superelastic property, which is particularly advantageous for re-centering capabilities and energy dissipation through hysteresis behavior. This study introduces a seismic isolation device that integrates SMA with an FPS isolation system (SMA-FPS) for seismic control of structures. However, few studies have been performed on the SMA-FPS isolation system to evaluate its seismic response, with the assumption that all system parameters are deterministic and precisely known. The system parameter uncertainties can influence the structural response and lead to inaccurate estimation of SMA-FPS. To emphasize the significance of uncertainties, this study performs parametric and optimization studies on the SMA-FPS isolation system. However, the optimal design of seismic isolation usually involves only minimizing the unconditional top storey root mean square acceleration (RMSA) as the performance function, which could lead to a significant variation in the response due to fluctuations in system parameter uncertainty. To obtain a more effective optimum design of SMA-FPS system, a robust design optimization (RDO) of SMA-FPS isolation system is performed, in which both mean value and variability of the performance function can optimize. The robustness of the SMA-FPS isolated building is achieved by making the system less sensitive to variations due to uncertain parameters. For this, the effectiveness of the proposed RDO approach and unconditional optimization approach are compared by analyzing a five-storey building equipped with SMA-FPS isolation system. The pareto fronts results shows, a significant reduction in performance variation is obtained through the proposed RDO approach, accompanied by a slight increase in RMSA responses, which improves the robustness of the SMA-FPS isolation system.