Analytical Fragility Curves for Multispan Continuous Steel Girder Bridges in Moderate Seismic Zones

Multispan continuous steel girder bridges are one of the most common bridge types in the central and southeastern United States. Seismic fragility curves for these highway bridges are essential for risk assessment of highway transportation networks exposed to seismic hazards. This study focuses on developing and comparing fragility curves for seismically and nonseismically designed bridges that are common in this region. The primary differences between seismically and nonseismically designed bridges are the column details and bridge bearings. Detailed three-dimensional (3-D) nonlinear analytical models, which account for the nonlinear behavior of the column, girders, and abutments, are developed with the use of the Open Sees platform. The fragility curves are developed with a suite of ground motions representative of the seismic hazard in the region. Unlike most previous studies, the fragility curves are developed with geometric variations such as column height, deck width, and length considered to study the effect of these variations on the fragility curves within the same class of bridges. The results provide insight into the level of uncertainty introduced in the analysis of fragility curves for portfolios of bridges with the use of 3-D analytical models and nonlinear time history analyses. Component and system fragility curves are obtained and are compared for the case of nonseismically and seismically designed bridges.