Dynamics of inelastic base-isolated structures subjected to recorded ground motions

Relations between the strength reduction factor Ry, the displacement ductility μ, and the vibration period Tn of a structure have been presented for fixed-base structures in numerous studies. These relations reflect the ranges of the inelastic response of a fixed-base structure to strong ground motion excitation. The superstructure of a base-isolated structure may also enter the inelastic behavior range when excited by strong ground motions. The goal of this study is to identify similar Ry–μ–Tn relations for base-isolated superstructures. A two-degree-of-freedom model of a base-isolated structure, with the inelastic behavior of the isolators and the isolated superstructure modeled in OpenSees, was used in this study. Recorded ground motions, whose parameters span a wide range of ground motion types, magnitudes and distances, were used to excite this model. Parametric studies were performed to determine the effects of isolator and superstructure design parameters on the response. A Ry–μ–Tn relationship for inelastic base-isolated superstructures is proposed using a format similar to such relations for fixed-base structures.