An equivalent linear model of lead-rubber seismic isolation bearings

An equivalent linear model for the seismic analysis of base-isolated bridges with lead-rubber bearings (LRB) is established in this paper using an identification method, Recognizing that the inelastic displacement spectra with constant ductility ratios of an earthquake ground motion can be approximated by the equivalent elastic spectra with appropriate effective period shifts (or effective stiffness) and equivalent damping ratios, the effective stiffness and equivalent damping ratio of lead-rubber isolation bearings are determined based on the identification of the inelastic displacement response spectra of 20 earthquake ground motions, In the identification formulation, a nominal strain hardening ratio of the LRB is used, The proposed equivalent linear model is characterized as a modification of the current equivalent linear model provided by the AASHTO isolation guide specifications so that the proposed model can be readily applied to the practical analysis and design, Numerical comparisons indicate that the proposed model in general can predict comparably accurately with the current practical methods. Copyright (C) 1996 Elsevier Science Ltd.