Seismic performance assessment of medical equipment using experimentally validated rolling and toppling nonlinear models

During the last decades, several hospitals stopped service due to severe seismic damage to nonstructural components and medical equipment. This article investigates the dynamic behavior of medical equipment deployed in a full-scale, five-story building with two different support conditions, base isolated (BI) and fixed to the base (FB). Two nonlinear mathematical models, namely, rolling and toppling, are used to simulate the observed experimental responses using recorded data and the camera projection technique (CPT). CPT generated the possibility of measuring equipment horizontal displacements, slips, rotations, rocking, and toppling responses. The Euler-Lagrange formulation, along with the Stribeck friction model, was used to numerically model the rolling and in-plane rotation behavior of a four-wheel mobile cart (4WMC), which is considered to represent the trajectory of equipment supported on caster wheels. Besides, a simple two-dimensional (2D) rigid block model was used to describe the rocking and toppling behavior of locked and free-standing equipment. It was found that the 4WMC model was sensitive to the platform and wheels' initial orientation angles, as well as the static and kinetic friction coefficients. As it should be, the toppling model was sensitive to the block dimensions and the intensity of the shaking. It was concluded that both numerical models successfully predicted the equipment rolling, in-plane rotation, rocking, and toppling behavior, as long as neither severe lateral impacts nor significant changes in the equipment mass occur during the motion.