Comparative seismic fragility analysis of conventional and base isolated hospital buildings having different structural systems

Abstract

After the 2010 Maule earthquake, Chilean authorities now require the implementation of base isolation systems in new public hospital buildings. However, in Chile the typical seismic force-resisting system of nonisolated hospitals is made up of reinforced concrete shear walls, whereas that of isolated buildings is made up of reinforced concrete frames. Since the former is much stiffer than the latter, there is then a question on the actual effectiveness of base isolation in reducing the seismic demands on new hospitals with respect to that on conventional hospitals, particularly the interstory drift demand under relatively low levels of ground shaking. Motivated by this context, this study evaluates the main results of a comparative analysis of the seismic performance of isolated and non-isolated hospitals considering the typical structural system in each case. Representative structural layouts were defined for both types of hospital buildings based on the Chilean state of the practice. Further, possible influence of the number of stories was considered. Member sizes and isolation system properties were determined in accordance to the current Chilean seismic design codes. The structural models were subjected to nonlinear time history analyses under two simultaneous horizontal components of ground motions selected from the Chilean database of earthquake records. The seismic response was evaluated through fragility curves, which were developed from results given by incremental dynamic analysis. Several limit states associated with the isolation systems, structural elements and nonstructural components of hospitals were considered. Results are compared with empirical observations on the effects of earthquakes on the Chilean building inventory, and the suitability of limit state thresholds defined in the literature is discussed.