Seismic Performance Index And Vulnerability Analysis Of Skew Bridge On Highway

In practical bridge engineering, deformation as an indicator is commonly used to safety evaluation. Because the dynamic response of each components of bridge has different sensitivity and damage degree, the two-level indicator has been proposed based on displacement and strain as safety evaluation. The skew bridges’ planar irregularities results in the bending-torsion coupling effect, which makes it difficult to determine the most unfavorable input direction that is based on deformation as seismic evalution indicator and based on ductility as seismic evalution method.In this paper, the nonlinear time history analysis of skew bridges with different skew angles was carried out firstly, and then by changing the input angle of the ground motion, the most unfavorable input direction of unidirectional ground motion and bidirectional ground motion was discussed. According to the relative displacement ductility ratio of the bridge pier and the allowable shear deformation value of the bearing, the damage index of the pier and the support was able to be determined, which got to the fragility curves of the bridge piers, bearings and the whole bridge, so the analysis of the bridge components and the overall performance could be done. The main research contents and conclusions are as follows:(1) Considering ground motion about the spatial effect, the trends of the deck rotation of superstructure, abutment unseating and pier displacement at the top are consistent between when is input by unidirectional ground motion with various angles and when is input by bidirectional ground motion with various angles:the overall deck rotation of the bridge is relatively small, the most unfavorable input direction of the abutment unseating is related to restraints of the bearings and while the most unfavorable input direction of the pier displacement at the top is perpendicular to the line bewteen the two columns of the bent pier, and the direction of the maximum displacement is also perpendicular to the line bewteen the two columns of the bent pier.(2) For the vulnerability analysis of the continuous skew bridge, selecting the PGA as the intesity index of ground motion and combined with domestic and international research on the damage condition and damage index, according to the relative displacement ductility ratio of the bridge pier and the allowable shear deformation value of the bearing, the damage index of the pier and the support was determined.(3) After the nonlinear time history analysis of the skew bridge under earthquake, the exceedance probability of different failure forms could be gotten. And then the fragility curves of each component and bridge system under earthquake action are obtained. We can know the failure probabilityof the overall bridge system is greater than the failure probability of a single component and the sliding bearing on the abutment is more prone to damage transversely.