UC San Diego

Seismic isolation is an established effective strategy to protect building structures from earthquake-induced damage by reducing accelerations and drifts within the superstructure. Current design codes primarily focus on ensuring operational resilience under design-level earthquakes with the building structure designed to remain essentially elastic. However, there is limited guidance for assessing the nonlinear behavior of the superstructure for beyond-design seismic events, which can be of concern since the structural performance can degrade rapidly from this point. This research investigates the performance of seismically isolated structures under extreme loading conditions, with emphasis on the response of the superstructure. The motivation for this research is to expand rapid assessment tool for the seismic performance evaluation of seismically isolated buildings. This expansion aims to enhance the understanding of limit state behaviors for beyond-design basis events.Utilizing a two-degree-of-freedom (2DOF) model, this study explores the dynamic interactions between the isolation system and the superstructure, highlighting the limitations and reliability of simplified models compared to full nonlinear analyses. Through Incremental Dynamic Analysis (IDA), the study evaluates various archetype buildings with different lateral force-resisting systems, examining the effects of parameters such as yield strength, ductility capacity, strength degradation, and moat wall pounding on the overall performance. The results indicate that while 2DOF models can provide a rapid assessment of the isolation system lateral displacements and superstructure drifts, they tend to underestimate roof accelerations and overestimate interstory drifts. Furthermore, the occurrence of moat wall impacts is shown to significantly affect the structural response, emphasizing the critical need for design strategies that mitigate or avoid such impacts. The research contributes to the broader understanding of seismic isolation, offering valuable insights into the performance of isolation systems under extreme seismic loading conditions.