Adaptive seismic isolation system combining gap dampers for pounding mitigation in base-isolated structures

Seismic base isolation systems have been widely used in structures located in highly earthquake-prone regions to mitigate the earthquake responses of superstructures. An effective isolation function is achieved at the expense of deformations that are mostly concentrated at the isolation layer due to the lower lateral stiffness of the isolation system. Hence, a sufficient clearance is required to accommodate this large deformation demand. However, isolation clearance may be limited because of practical and architectural constraints. Therefore, moat wall (MW) pounding potentially occurs in base-isolated structures under extreme earthquakes, inducing increased story drifts and floor accelerations of the superstructures. Considering this reason, this study presents an adaptive seismic isolation system that combines gap dampers (GDs) for mitigating pounding in base-isolated structures. The GD isolation system incorporates steel U-shaped GDs into a lead rubber bearing system where steel U-shaped dampers (UDs) provide additional stiffness and energy dissipation when bearing deformation exceeds a certain threshold. Quasi-static cyclic tests were conducted to explore the hysteretic responses and fatigue behavior of UDs under cyclic loading. Experimental results confirm that the UDs exhibit stable energy dissipation and high fatigue capacity under different loading conditions. Subsequently, seismic performances of two base-isolated buildings designed with GDs and MWs were investigated computationally under far- and near-field earthquakes. The results reveal that compared with the conventional MW pounding in the isolation layer, the GD isolation system can effectively mitigate the responses of the isolation layer and the superstructure. Finally, parametric analyses were performed to investigate the sensitivity of various mechanical properties of GDs to isolation effectiveness.