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Proceedings of the International Conference on c-11
Advances and New Challenges in Earthquake
Engineering Research, Hong Kong Volume
EVALUATION OF SUPPLEMENTAL ENERGY DISSIPATION
DEVICES IN PROTECTING HIGHWAY BRIDGES WITH
SOIL-STRUCTURE INTERACTION
Jian Zhang and Nicos Makris
Department of Civil and Environmental Engineering, University of California, Berkeley
Berkeley, CA 94710, USA
ABSTRACT
This paper presents the response analysis of a freeway overcrossing equipped with isolation bearings and
fluid dampers in order to evaluate the efficiency of supplemental energy dissipation devices to suppress
the seismic response of highway bridges. Recognizing that the soil-structure interaction affects
appreciably the earthquake response of highway overcrossings, the study employs an elementary stick
model enhanced with frequency-independent springs and dashpots that approximate the dynamic
stiffnesses of approach embankments and pile groups. The nonlinear behavior of columns as well as
hysteretic behavior of seismic protection devices (elastomeric bearings and viscous fluid dampers) are
included in the study. The emphasis is placed to understand the effect of supplemental damping in
association with the ability of the structure to dissipate energy through soil-structure interaction. It is
concluded that the fluid dampers are effective in controlling displacement demands, however the
flexibility of the approaching embankments is responsible for partially reducing their efficiency.
INTRODUCTION
Earthquake damage in most highway overcrossing is the result of excessive seismic displacements and
large force demands that have been substantially under-estimated during past design. A direct
consequence of the under-estimated seismic displacements, which were the combined result of poor
representation of the kinematic characteristics of the ground, low lateral forces, and overestimated
stiffnesses, was that the seating length at the deck supports was unrealistically short and the lateral
separation between adjacent structures were typically inadequate, resulting in loss of support or pounding
(Maragakis and Jennings 1987). These geometrical inconsistencies resulted in spectacular failures that
have been witnessed during the recent 1989 Loma Prieta and the 1994 Northridge earthquakes in
California and the 1995 Kobe earthquake in Japan.
In view of these failures many research programs were launched after the 1971 San Fernando earthquake
to study the seismic resistance of highway bridges. Improvements have been achieved in both design and
analysis of bridge structures with the help of strong motion records. Extensive retrofit programs have
been implemented in California, which include jacketing of columns and the use of composite materials
(FHWA 1995). While retrofit programs are underway there is ongoing need for better understanding the
behavior of each substructure elements of the bridge and to what extend its individual behavior affects the
overall response of the bridge structure. In particular, the increasing need for safer bridges in association