Fragility Analysis of a Base-Isolated Integral Bridge under Two-Component Far- and Near-Field Excitation

Fragility analysis of base-isolated integral bridges under two-component earthquakes for far- and near-field earthquakes has been scantly reported. In this study, the performance of a base-isolated integral bridge was determined using fragility analysis for one- and two-component earthquakes. Three types of ground motion were considered, namely, far-field earthquakes, near-field earthquakes with directivity effects, and fling-step effects. Peak ground acceleration of time history was selected as the intensity measure, and maximum deck drift and shear strain in the isolator were considered as damage measures. The relations between damage measures and intensity measures were established using incremental dynamic analysis (IDA). Eleven time histories of each type of ground motion were considered for IDA. Regression analysis was conducted on the results of IDA to obtain a probabilistic seismic demand model and fragility curves for four levels of both damage measures. The main finding of the study was that due consideration should be given to the design of base isolators for near-field earthquakes, because they pose more of a threat to base-isolated integral bridges compared to far-field earthquakes.