Study of elastoplastic bridge seismic isolation system

Seismic isolation bearings consisting of lubricated sliding bearings and steel dampers exhibit nearly elastoplastic behavior. Accordingly, they can transfer force to bridge substructures which is independent of the level and frequency content of seismic excitation. While this is a desirable property, it is achieved at the expense of potential for development of significant permanent displacements. This paper reports on a study of one such system that consists of E-shaped steel dampers and which found a number of applications in bridge seismic isolation. The paper demonstrates that indeed significant permanent displacement develop, particularly in earthquakes with shock-loading characteristics. Moreover, the paper demonstrates the significance of restoring force in isolation systems and concludes that the current American Association of State Highway and Trans-portation Officials (AASHTO) design guidelines for these systems are appropriate.