Seismic response assessment and recommendations for the design of skewed highway bridges

Seismic vulnerability of highway bridges remains an important problem and has received increased attention as a consequence of unprecedented damage observed during several major earthquakes. A significant number of research studies examined the performance of skewed bridges under service and seismic loads. It is noted that results of these studies are particularly sensitive to modeling assumptions in view of the interacting parameters with the skew. The present study investigates the seismic response characteristics of two-span skewed post-tensioned box-girder bridges with skew angles varying from 0 to 60 degree. To facilitate a comprehensive analytical investigation simplified modeling techniques are introduced. The accuracy of simplified beam-stick models are verified against counterpart finite element models. Effect of various parameters on the overall seismic performance was examined and implications were presented. Finally, nonlinear time history analysis was used to generate system fragility functions for a range of three-span highway bridges (straight, moderate skew, and significant skew). It is shown that simplified beam-stick models have the capability to capture the nonlinear time history response of skewed bridges. Using incremental dynamic analysis (IDA) method, fragility functions were developed and the effect of the skew on the vulnerability of highway bridges is investigated. Furthermore, analytical fragility functions of skewed bridges were compared to HAZUS fragility functions. The soil type, presence of shear keys, and aspect ratio are determined to have a significant effect on the seismic performance of skewed bridges. Also, it was concluded that highway bridges with large skew angles (> 30°) are more vulnerable to seismically induced damages compared to those with moderate skew angles (< 30°).