Nonlinear Seismic Response of Skewed Highway Bridges Subjected to Bidirectional Near-Fault Ground Motions

Past earthquakes have repeatedly demonstrated that skewed bridges are more vulnerable to earthquake-induced failure than straight bridges because of their complex, irregular geometries and unique load-transfer mechanisms. This study focused on analyzing the seismic performances of prestressed concrete box-girder highway bridges with seat-type abutments under bidirectional near-fault ground motions, especially with respect to abutment skew angle, gap size at the expansion joint between the superstructure and the abutment in the longitudinal direction, and initial gap size between the the superstructure and abutment shear keys in the transverse direction. Three dimensional models of single- and two-span bridges with seat-type abutments were developed considering nonlinear characteristics of skew-angled abutments, bridge key components, abutment-soil interaction, soil-pile interaction, and the pounding effect between the superstructure and the abutments. Nonlinear time-history analyses were performed for various skewed highway bridge models using seven sets of near-fault ground motions with two horizontal components. Results showed that the skew angle and gap size in longitudinal and transversal directions have significant impact on the seismic behavior of skewed highway bridges. The deck displacement in the longitudinal direction and rotation response will increase with the increase of the skew angle, but the transverse displacement response exhibits a more severe response after the skew angle reaches 30°. The longitudinal deck displacement and rotation of skewed bridges increase with decreasing gap size at the expansion joint in a longitudinal direction. Furthermore, the behavior of shear keys may have an important effect on the overall seismic response of skewed highway bridges, especially the probability of collapse due to excessive deck rotation.