Experimental Study on the Seismic Response of Equipment on Wheels and Casters in Base-Isolated Hospitals

Base isolation is accepted as the method of choice for mitigating the seismic risk of critical facilities, including hospitals. However, while many studies have confirmed the effectiveness of isolation in reducing seismic demands on attached nonstructural components, only a few have investigated the performance of unanchored building equipment and contents (ECs), and especially mobile ECs supported on wheels/casters, in base-isolated buildings. Motivated by the fact that about one-third of ECs in typical hospitals are supported on wheels/casters, this study investigated the seismic response of such ECs in base-isolated buildings through shake table tests. A comparative approach was adopted to examine the performance of lead-rubber bearing (LRB) and triple-friction pendulum (TFP) isolation systems against a conventional fixed-base hospital in reducing displacement and velocity demands on mobile ECs. It was observed that base isolation is effective in reducing seismic demands, especially velocity, on ECs. It was concluded that, in base-isolated buildings, locking the wheels/casters on ECs reduces EC response. Fragility curves were developed for mobile ECs on unlocked wheels and casters in base-isolated buildings.