Seismic vulnerability of fixed-base and base-isolated hospitals: blind comparison between shaking table and numerical tests

Abstract

New hospitals are frequently designed using base-isolation systems to improve their structural response in future seismic events, contrary to the observed rather poor seismic performance of several fixed-base hospitals. Despite this evidence, a fair question arises about the convenience, or not, of using these modern seismic protection technologies as opposed to other conventional structural design solutions, on the grounds of a holistic approach based on structural and nonstructural damage expected as well as continuity of service to the community in the aftermath of an earthquake. The current study aims to an integrated numerical assessment in a hospital setting, with particular attention to evaluating and classifying functionality of nonstructural components and critical medical equipment. Two scaled four-storey (fixed-base) and three-storey (base-isolated) hospital framed buildings were built and subjected to shaking table tests at the University of Kyoto (Japan). A two-phase experimental campaign with numerical structural and nonstructural blind prediction took place, considering two earthquakes scaled at different intensity levels. To this end, a self-built C++ code is developed to account for lumped plasticity modelling of steel frame members and variability of the friction coefficient of curved surface sliding bearings. Moreover, three contest nonstructural components are modelled in the fixed-base structure: i.e. elastic single degree of freedom systems representing two tanks filled with sand (top floor); elastic beam elements for piping (third floor); five-element macro-model for the in-plane-out-of-plane nonlinear response of partition walls (first floor). Finally, a self-built MATLAB code is employed in order to analyse sliding, rocking and jumping motion of three contest medical equipment (i.e. incubator at third floor; dialysis machine at second floor; surgical bed at first floor), on the basis of acceleration time histories of selected structural nodes of the fixed-base structure.