Seismic fragility assessment of base-isolated structures subjected to uneven settlement of foundation based on a synergistic multi-indicator damage model

The implementation of base isolation technology in high-intensity seismic areas underlain by collapsible loess is hindered by a critical challenge: the subsoil in these regions is susceptible to uneven settlement of foundations (USF), which can induce structural deformation, damage, and functional failure. To address this issue, a comprehensive numerical evaluation framework is proposed. The USF is introduced into a finite element model to examine the seismic response of a representative base-isolated structure. Based on these simulations, a synergistic multi-indicator damage model is developed by coupling inter-story drift ratio demand with cumulative energy dissipation. This model is subsequently employed to generate seismic fragility curves under combined earthquake-USF scenarios. The analysis indicate that USF markedly accelerates damage accumulation in both the isolation layer and the superstructure. The proposed model reliably captures the initial tilt induced by settlement and exposes incipient damage patterns at an early stage. Moreover, even settlements within code-prescribed tolerances are found to precipitate earlier damage onset and to some extent reduce the seismic performance of the system.