Seismic Vulnerability Assessment of Skew Bridges

Abstract eng:
The operability of the highway network after an earthquake is extremely important. The rescue operations and basic supply after a disaster mainly depend on the proper functioning of the highway network and its bridges. Past earthquakes have shown, that bridges are the most vulnerable components in a transport network and highly susceptible for severe damage during seismic events. Especially skewed bridges are at higher risk than straight bridges due to effects engaged by the activation of coupled transverse and longitudinal modes. The fragility curves for the skew bridges with a skew angle of 0°, 12.33° and 45° have been developed. Fragility curves are the most reliable tool for seismic vulnerability assessment, when a rapid estimation is needed. For the present investigation fragility curves for four different damage states ranging from slight damage to complete destruction have been developed. An investigation of the effect of skew angle on the seismic vulnerability has been carried out by comparing the fragility curves for bridges with different skew angles in the different damage states. As the bridge piers and bearings are the most vulnerable components, different fragility curves for each of these components have been adopted for the analyses. A non-linear 3-D finite element bridge model was used for the investigation in order to be able to include all torsional effects arising from the bridge skew. Up to 60 synthetic acceleration time history analyses have been applied on the different bridge configurations. Peak responses from all time histories for each vulnerable component has been extracted and reviewed. Regression analyses of the peak responses have then been carried out to develop a probabilistic seismic demand model (PSDM). The developed fragility curves have been applied in the framework of a case study to a typical European highway bridge. The evaluation of the selected bridge shows that the bridge bend is extremely vulnerable to the seismic intensity range of 0.2 g to 0.4 g. But for bearings the range of seismic intensity which will cause severe damage is 0.45 g to 0.7 g. The effect of skew angle on the overall seismic vulnerability has been analyzed by comparing the fragility curves of the different bridge configurations

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