Optimal design of the seismic protection system for isolated bridges

Earthquakes and Structures, Vol. 7, No. 6 (2014) 969-999

DOI: doc.docsou.com 969

Optimal design of the seismic protection system

for isolated bridges

Daniele Losanno, Mariacristina Spizzuocoa, Giorgio Serinob

Department of Structures for Architecture and Engineering, University Federico II,

Via Claudio 21, 80125, Naples, Italy

(Received February 13, 2014, Revised June 1, 2014, Accepted June 10, 2014)

Abstract. Aim of the paper is the definition of optimal design parameters characterizing the isolation

system of a bridge, both in the case of elastomeric (VI) and sliding bearings (SI), having viscoelastic or rigid-plastic behavior, respectively, installed between the piers and the deck. The problem is treated by means of an analytical approach. Using the frequency response analysis, a simple procedure is proposed to determine the optimal value of the viscous coefficient or the yield displacement of the isolators. The adequacy of the proposed procedure is finally verified through time-history analyses performed on a practical case under natural earthquakes.

Keywords: seismic response; isolated bridge; optimal design; damping; elastomeric bearings; sliding

bearings

1. Introduction

The seismic protection of bridge decks by using passive isolation systems represents a widely studied technique since the Eighties (Bhuiyan and Alam 2013), even though different more complex control strategies (e.g., semi-active and active ones) have been investigated and implemented in civil structures in the last twenty years (Li and Liu 2011; Li, Liu and Lan 2012). The design of a passive isolation system for bridges is often treated as an optimization problem: once the objective of the optimization is defined, together with the constraints imposed by the problem, the design methodology is developed with the aim to determine the optimal mechanical characteristics of the protection devices. In the following, some proposals of different researchers will be summarized, first reporting those adopting optimization concepts in formulating the design criteria.

Ciampi and De Angelis (1996) and Ciampi (1998) proposed an energy-based methodology for the optimal design of dissipation devices used as base isolation systems of typical bridges. The approach consisted in the maximization of an appropriate nondimensional energy index defined as the ratio between the energy dissipated by the isolators and the input energy to the controlled

Corresponding author, Ph.D. Candidate, E-mail: daniele.losanno@unina.it a

Ph.D., E-mail: spizzuoc@unina.it b

Professor, E-mail: serino@unina.it

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