Base-isolation of a hospital pavilion against in-plane-out-of-plane seismic collapse of masonry infills

The in-plane (IP) and out-of-plane (OOP) seismic collapse of masonry infills (MIs) may induce devastating economic and social consequences for public buildings such as hospitals in the aftermath of an earthquake. Yet no attention has been paid in the literature to base-isolation as a retrofitting technique for improving the IP and OOP response of these nonstructural components. To full this gap, a medical centre with a five-storey r.c. framed structure is first designed as fixed-base in a medium-risk zone, in compliance with a former Italian code. Four infill aspect ratios are examined, combining bays of different lengths with exterior and interior configurations of MIs in the perimeter frames. Four structural models of the hospital are considered: i.e. two bare structures with nonstructural MIs, fulfilling provisions of the former and current Italian codes for limiting nonstructural damage; two infilled structures, with the above configurations of structural MIs, applying only provisions of the former Italian code. To achieve full operational capacity in a high-risk seismic zone, these structures are retrofitted with base-isolation systems of high-damping-rubber bearings. To assess the integrity of the MIs a five-element macromodel predicts their IP and OOP nonlinear force–displacement laws and describes the effects of simultaneous or prior in-plane (IP) damage on the OOP behaviour. OOP drift- and acceleration-sensitivity of MIs are investigated through nonlinear dynamic analyses of the fixed-base and base-isolated hospitals subjected to far-fault and nearfault earthquakes corresponding to the life-safety limit state provided by current Italian code for strategic facilities. High levels of vulnerability and early IP and OOP collapse of MIs are obtained for all design procedures of the fixed-base structures, while a different distribution of the IP and OOP damage of MIs but no collapse in presence of a base-isolation system is observed depending on the formulation adopted for their nonlinear behaviour.