Seismic Response of a Non-Concentric Rolling Isolator System

Abstract

Suspending a structure in the form of a pendulum would provide excellent protection from seismic ground motion, but is impractical for structures of any significance. The effect can be replicated in other ways, such as by placing the supports on shallow spherical dishes (the so-called friction pendulum), or by means of shaped, non-circular rollers placed between a building and its foundations. This paper investigates the dynamic response of structures resting on seismic isolators consisting of rollers with non-concentric, spherical upper and lower surfaces. The governing equations are developed, revealing a softening system with a period that is independent of mass. Expressions for period and stiffness as nonlinear functions of displacement are developed along with linear approximations. The roller element is then incorporated into a nonlinear time-history integration algorithm which is used to compare the response of an example structure on rolling isolators with a structure on conventional constant stiffness isolators. Peak acceleration response is significantly reduced, especially for high intensity earthquakes, with smaller reductions in peak displacement.