Structural and non-structural numerical blind prediction of shaking table experimental tests on fixed-base and base-isolated hospitals

Abstract

Base-isolated hospitals are frequently preferred to fixed-base ones because of their improved seismic structural performance. Despite this, the question remains open on the advisability of using this modern seismic protection technology in preference to other conventional solutions, on the grounds of a holistic approach based on limiting non-structural damage as well as continuity of service to the community in the aftermath of an earthquake. Two full-scale four-storey (fixed-base) and three-storey (base-isolated) hospital buildings have been recently built and subjected to three-dimensional shaking table tests at the National Research Institute for Earth Science and Disaster Prevention (Japan), with particular attention to evaluating and classifying functionality of non-structural components and vital medical equipment. A two-phase experimental campaign was carried out considering two earthquakes scaled at different intensity levels and applied along the horizontal and vertical directions. The current study aims to provide results of a numerical structural and non-structural blind prediction of these hospital settings. A homemade numerical code is developed to account for lumped plasticity modelling of steel frame members and variability of the friction coefficient of spherical sliding bearings. Moreover, three non-structural components are modelled in the fixed-base structure: that is, elastic single degree of freedom systems representing two tanks filled with sand at the top floor; elastic beam elements for piping at the third floor; five-element macro-model for the in-plane-out-of-plane nonlinear response of partition walls at the first floor. The identification of predominant vibration periods of the fixed-base structure is carried out using a homemade numerical code based on the continuous wavelet transforms in combination with the complex Morlet wavelet. Finally, the sliding and rocking motion of three items of medical equipment (i.e., incubator at third floor, dialysis machine at second floor and surgical bed at first floor) are analysed by means of a homemade numerical code, considering acceleration time histories of selected structural nodes of the fixed-base structure.