Experimental investigation of the inelastic behavior of structures isolated using friction pendulum bearings

Current US and European seismic design codes limit the magnitude of strength reduction allowed for seismically isolated structures, thus effectively leading to the elastic design of these structures. This study is focused on the experimental investigation of the behavior of seismically isolated structures when they behave inelastically. The experimental investigation performed in this study is based on the response of a reduced-scale seismically isolated steel structure to strong analytical pulses and recorded ground motion accelerations applied using the shaking table of the ETH Zurich IBK Structural Testing Laboratory. The part of the structure designed to develop inelastic behavior is a pair of steel coupons that can be easily replaced after such damage. The structure is seismically isolated using four friction pendulum bearings designed to accommodate the large displacements induced by strong ground motion excitations. The bearings are made by MAGEBA SA. A relation between the experimentally obtained strength and displacement ductility of inelastic seismically isolated structures is presented in this paper. The influence of design parameters, such as the fundamental vibration period of the isolated superstructure, and the types of ground motion is quantified and presented. The experimentally obtained data is compared to an analytically derived strength-ductility-period relation for seismically isolated structures. This comparison will serve to validate the proposed analytical relation and to further the understanding of the behavior of inelastic seismically isolated structures