Effect of Ground Motion Spatial Distribution on the Fragility of Skewed Highway Bridge Components under Far-field and Near-field Ground Motions

The aim of this study was to determine the effects of uncertainty of incident angle on maximum values of engineering demand parameters (EDPs) in highway bridges. Thus, 80 ground motion pairs (40 far-field and 40 near-field ground motion pairs) are imposed on numerical models of a set of skewed bridges (0 to 60 degrees) in 12 various directions (0 to 180 degrees) by performing non-linear dynamic analyses. The components of fragility curves were obtained and compared to the results of the imposed excitations in the principal directions. The difference was up to 65%. Also, using rotation of response axes, the created demands in different directions (0 t0 360 degrees) were calculated to investigate the effect of rotation of response axis on bridge reponse. Results showed that there is 39% between excitation intensities in 50% failure probability in bridge column, when excitation is in different directions on the structure and the response axis is rotated to record maximum response, and the case where direction of imposing the excitation and recording demand correspond to longitudinal and transverse directions of the bridge. Also, this difference has direct relationship with increase of skew angle of the bridge.