Influence of Soil-Structure Interaction and Liquefaction on the Isolation Efficiency of a Typical Multispan Continuous Steel Girder Bridge

Abstract

Isolation has been identified as a popular retrofit measure for seismically deficient bridges. However, most isolation designs neglect soil-structure interaction (SSI) effects. The feasibility of isolation for bridges with SSI, especially in liquefaction-prone regions, requires further study. This paper investigates effects of SSI and liquefaction on the fragility of both an unretrofitted and an isolated coupled bridge-soil-foundation (CBSF) system. Results of the fragility analyses reveal that the failure probability of the isolated system is less than that of the nonisolated one for both stiff soils and soft soils, whereas SSI tends to simultaneously decrease isolation effectiveness. Results also show that liquefaction provides an effective natural isolation by reducing the curvature demands on the columns, although it increases the isolation bearing displacement and pile curvature. Therefore, SSI should be considered in the design of isolated bridges, as appropriate isolation in conjunction with the CBSF system could still offer a viable retrofit option by replacing the vulnerable steel bearings and reducing critical component demands, such as columns, even if liquefaction occurs.