Life-cycle cost based design of bridge lead-rubber isolators in seismic regions

While rubber isolators are widely used for the seismic protection of bridges, their influence on the total life-cycle costs (TLCC) is generally neglected. This study aims to provide a framework to obtain the most cost-effective design solutions of Lead-Rubber Bearing (LRB) isolators for minimum objective functions based on the life-cycle cost of bridges. Also, a comprehensive analytical study is conducted to assess the effects of LRB characteristics on the total life-cycle costs (TLCC) consisting of the initial costs of LRB isolators and structural elements, traffic damage costs, and structural and non-structural damage costs due to possible earthquake events during the bridge life-span. While changing the lead core diameter, confined diameter, and the total thickness of the rubber layers could influence the TLCC of the bridges, the effect of lead core diameter is shown to be more significant. By using lead core diameter as the main design parameter, increasing the initial cost of LRBs up to a certain level can significantly reduce (up to 38%) TLCC of the bridges. However, beyond this limit, the TLCC may increase. Based on the results of over 13,000 Reinforced Concrete (RC) bridges under different earthquake hazard levels, the best design solutions are identified for different design objectives. The results of this study should prove the benefit of the proposed method for a more efficient design of bridges with lower TLCC.