Analytical Fragility Models for Box Girder Bridges with and without Protective Systems

Fragility analysis for highway bridges is essential for risk assessment of highway transportation networks exposed to seismic hazards. This study uses detailed three-dimensional nonlinear analytical models of a typical California multi-span concrete box girder bridge without and with protective systems to develop fragility curves which can be used in regional seismic risk assessment of transportation networks. The analytical as-built bridge model is calibrated using responses recorded during the 1979 Imperial Valley earthquake. Fragility analysis for the as-built bridge model and two retrofitted bridge models is carried out. The fragility curves for the reference bridge indicates that the bridge is robust compared to many other bridge types found in other parts of the United States. Also, compared to the as-built fragility, the steel jacketing retrofit reduces the fragility slightly, while the elastomeric isolation bearing retrofit also significantly reduces the fragility of the bridge.