Seismic vulnerability of RC skew-bridges considering the vertical component of ground motion

Even after considering speed, safety, construction problems and space constraints, it is not always possible to align bridge piers to being exactly normal to the bridge deck axis. The solution to this is a skew bridge. This study investigated the vulnerability of an RC skew bridge with a skew angle of 45 under seismic loading using fragility curves with and without consideration of the vertical component of ground motion. Non-linear time history analysis was used with a set of ten near-field ground motions. The column ductility displacements determined as the damage index and fragility curves for the slight, moderate, extensive and complete damage state levels were calculated and assessed. A comparison between the fragility curves of bridges with skew angles of 0° and 45° with and without the effect of the vertical component indicated that the probability that demand would exceed the capacity increased at all damage states levels for the skew bridge in both the longitudinal and transverse directions compared to the bridge with no skew angle. By considering the vertical component of the ground motions and for lower damage states (slight and moderate), the vulnerability of the bridge was not increased remarkably. However, for higher damage states (extensive and complete), the vulnerability was increased remarkably by considering the vertical component of the ground motions. In other words, the higher a damage state is, the more difference can be seen between the probability parameter (vulnerability) in skew bridge subjected to ground motions with and without the consideration of the vertical component. Additionally, the seismic behavior of bridges with skew angles of 0°, 15°, 30° and 45° were compared using the average pier displacement and it was shown that there was no linear relationship between an increase in the skew angle and an increase in relative displacement.