Evaluation of Simplified Methods
for the Design of Bridges
with Seismic Isolation Systems
Donatello Cardone,
a)
Mauro Dolce,
b)
and Giuseppe Palermo
a)
In this paper, simplified methods for the design of bridges equipped with
strongly nonlinear isolation systems (IS) are examined. Reference is made to
the single mode method (SMM), adopted in many seismic codes and
guidelines for the analysis and design of bridges with flexible substructure.
Two different design approaches are considered, one aimed at controlling the
maximum force transmitted by the IS to the pier, while the other the maximum
pier-deck displacement. The background of the SMM and the implementation
of the two design approaches are presented first. This is followed by a series of
examples of application and validation studies through nonlinear time-history
analyses (NTHA). The variability of the mechanical behavior of the IS with air
temperature is taken into account in both design procedures and NTHA. The
NTHA results point out that simplified methods of analysis can be reliably
used for bridges with IS, to satisfy the design performance objectives over the
whole operation range of temperature, once a proper design temperature is
selected. DOI: 10.1193/1.3106202
INTRODUCTION
Seismic isolation (Naeim and Kelly, 1999) is a modern technology that can be used
to reduce seismic effects on structures. In bridges, seismic isolation is applied with the
main scope of reducing the high inertia forces transmitted by the deck to piers and foun-
dations. Several types of isolation systems (IS) are in use today and many new solutions
are continuously being proposed and investigated (Higashino and Okamoto 2006). Most
currently used IS for bridges include (Chen and Duan 2003, Priestley et al. 1996, Naeim
and Kelly 1999, Higashino and Okamoto 2006, Kelly 2001): (i) lead-rubber isolators
(LRIs), (ii) high-damping rubber isolators (HDRIs), (iii) friction pendulum isolators
(FPIs), sometimes coupled with viscous dampers, and (iv) combinations of flat sliding
bearings (FSBs) with different auxiliary recentring and/or energy dissipating devices. IS
based on curved or flat sliding bearings present some advantages with respect to rubber-
based IS, such as a peak response of the bridge less sensitive to substantial variations in
the frequency range and intensity of the ground motion (Park et al. 2002). On the other
hand, rubber-based IS do not require continuous maintenance to assure a suitable state of
lubrication of the steel-PTFE surfaces and their installation is easier.
a)
DiSGG, University of Basilicata, Macchia Romana Campus, 85100 Potenza, Italy
b)
Italian Dept. of Civil Protection, via Vitorchiano 4, 00189 Rome, Italy
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Earthquake Spectra, Volume 25, No. 2, pages 221–238, May 2009; © 2009, Earthquake Engineering Research Institute