Razi University

Enhancing the seismic safety of bridges, as one of the key components of tra  ortation networks, is of particular importance. One of the most effective approaches for reducing the seismic response of bridges is the use of seismic isolation. Among the conventional isolation systems widely employed for the seismic retrofitting of bridges in earthquake-prone regions are lead-rubber bearings (LRBs). The primary objective of this dissertation is to investigate the feasibility of replacing LRBs with a novel type of elastomeric bearing to achieve uninterrupted operational performance under the design-basis earthquake in an isolated bridge, considered as a case study. The proposed isolators are mesh-reinforced elastomeric bearings equipped with U-shaped metallic dampers (MRBs). The boundary conditions of the MRB isolators are designed as partially bonded, such that under shear loading, the development of pseudo-rolling deformation results in a reduction in their effective horizontal stiffness. To establish a rational basis for comparison, the LRB and MRB isolation systems were designed to exhibit similar lateral stiffness and effective damping at the maximum considered earthquake (MCE) hazard level at the project site. The lateral force–displacement hysteresis curves of the isolators were obtained through finite element analyses conducted using ABAQUS. The seismic performance of the isolated bridges was evaluated through Incremental Dynamic Analysis (IDA), including the development of fragility curves, determination of the Collapse Margin Ratio (CMR), and assessment of the corresponding failure modes based on numerical models developed in OpenSees. The results of the study indicate that both isolation systems satisfy the criteria for uninterrupted operational performance under MCE-level ground motions. The mean Collapse Margin Ratios of both systems, considering the occurrence of failure in the seismic isolators, were calculated to be greater than 3.0. The seismic responses of the substructure components of the bridge equipped with the MRB system were more effectively controlled, and the spectral acceleration corresponding to a 50% probability of isolator failure was approximately 16% lower than that obtained for the LRB system. An economic comparison of the two isolation systems indicates an approximately 38% reduction in the total cost and an approximately 30% reduction in the weight of the MRB compared with the corresponding LRB. Based on the findings of this study, MRBs demonstrate sufficient potential to serve as a technically and economically viable seismic isolation system for bridges.