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Seismic Vulnerability Assessment of Skewed Reinforced Concrete Bridges

Skewed bridges are commonly used in highway interchanges where the straight (unskewed) bridges are not suitable. There have been several observations of heavy damage of bridges that have geometric irregularities, especially significant skewness. Such damage severely disrupts transportation systems, leading to substantial economic consequences. Skewed bridges are often inevitable due to the complexity and lack of orthogonality of transportation networks; hence better quantification of the effects of skewness on the bridge performance is a more viable approach than avoiding skewed bridges. This research focuses on the seismic vulnerability analysis of skewed reinforced concrete (RC) bridges. From the straight to highly skewed, various bridge models are created based on design example No. 4 prepared by the US Federal Highway Administration (FHWA). A set of earthquake ground motion records is carefully selected to impose consistent seismic demands on bridges. The fragility relationships for all bridge configurations are derived from the non-linear dynamic response history analysis. A new structural reliability method is utilized to handle the computational challenge in deriving fragility curves, which incorporates the structural analysis and reliability analysis to calculate the failure probability efficiently and accurately with the first-order reliability method (FORM). An attempt is made to parameterize the problem based on the skew angle. It is shown that the skew angle has a direct effect on the seismic vulnerability of RC bridges. The results reported will be helpful for new designs of skew RC bridges.