Seismic isolation beatings consisting of lubricated sliding bearings a
nd steel dampers exhibit nearly elastoplastic behavior. Accordingly, t
hey 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 d
evelopment 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 characteristic
s. Moreover, the paper demonstrates the significance of restoring forc
e in isolation systems and concludes that the current American Associa
tion of State Highway and Transportation Officials (AASHTO) design gui
delines for these systems are appropriate.