Probabilistic seismic performance assessment of optimally designed highway bridge isolated by ordinary unbonded elastomeric bearings

Abstract

Following the idea of using unbonded isolators to eliminate the tensile stress and providing a cost-effective isolation system, recent experimental research has shown ordinary unbonded steel reinforced elastomeric bearings (SREBs) as an attractive option for seismic isolation of highway bridges. The focus of current research work is on the evaluation of the seismic vulnerability of a highway bridge isolated by unbonded SREBs through developing fragility curves of the structure. This assessment considers parameters playing a key role in the isolation system behavior, namely the friction coefficient, as well as the isolator aging effects. In this regard, a typical three-span highway bridge is considered and designed with the rubber bearing isolation system by applying a multi-objective optimization procedure to reduce the seismic isolation deformation as well as the base shear simultaneously. The nonlinear models for bridge piers and isolation devices are incorporated. An Incremental Dynamic Analysis (IDA) method is applied to generate the fragility functions using a suite of 20 ground motion records. The results show that this type of base isolation system is well capable of mitigating earthquake excitation. Additionally, the overall performance of the bridge is not sensitive to the friction coefficient, while the aging of the isolator units caused an increase in the bridge vulnerability.