A comparison of pre- and post-seismic design considerations in moderate seismic zones through the fragility assessment of multispan bridge classes

Vulnerability estimation as well as quantitative and qualitative assessment of the seismic risk to highway bridges is crucial in obtaining reliable estimates of the resilience of highway transportation systems. Although previous studies have evaluated the seismic response and fragility of various bridge classes common to the central and southeastern United States, there is very little research that explores the differences in performance of bridge classes built with and without seismic detailing. This paper addresses this gap by investigating the influence of seismic detailing of four multispan bridge classes on the seismic performance, as well as the failure probability through the development and comparison of fragility curves. The primary differences between seismically and non-seismically designed bridges are the column reinforcement details and bridge bearings. Component and system fragility curves are developed to provide insight into the difference in performance of non-seismically and seismically designed bridges and are compared with those currently found in HAZUS-MH. Confidence bounds are finally developed to characterize the uncertainty about the proposed median fragility curves for the bridge classes. Bridge classes with seismic provisions incorporated in their design tend to have reduced confidence bandwidth at higher damage states. Significant improvement in performance is seen in all bridge classes considered in this study when seismic design and details are used.