SEISMIC RESPONSE OF ISOLATED STRUCTURES UNDER SUBDUCTION AND CRUSTAL GROUND MOTIONS: ANALYSIS OF A CASE STUDY STRUCTURE

Abstract

Seismic isolation aims to uncouple the motion of the structure from the ground shaking and thereby reduce structural forces, accelerations, and deformations of buildings under strong earthquakes. Seismic isolation represents an effective strategy to protect buildings structures, and the related contents from earthquake damage and consequently reduce seismic losses. Nowadays, most of Chile’s newly designed hospitals incorporate seismic isolations to minimise structural and non-structural damage and ensure operational continuity even after major earthquakes. Seismicity in Chile is strongly dominated by subduction megathrust events, and most structures, including newly designed hospitals, have been designed and verified by considering the seismic hazard resulting from such earthquakes. However, seismologists have recently highlighted another potential seismic hazard, such as earthquakes originating from the San Ramon Fault (SRF), a crustal fault that lies less than 15 km from the city of Santiago and that was recently declared as potentially active. The present study investigates the seismic performance of a real case study seismically isolated hospital in Santiago, Chile, considering sets of ground motion (GM) records generated by either megathrust earthquakes from the subduction margin or crustal fault mechanism. A 3D finite element model of the case study hospital is developed in OpenSees, including detailed modelling of the seismic isolation system. Sets of recorded subduction GMs, and physics-based synthetic crustal GMs, are selected to perform inelastic response history analyses on the case-study hospital. Local and global Engineering Demand Parameters (EDPs) from the two sets of GMs are compared between them and with code-based capacity limits used during the design. The results show the importance of considering different seismic sources (subduction vs crustal) to better understand/predict the response of isolated structures to GMs.