Representation of Incidence Angle in Seismic Analysis of Skewed Highway Bridges

Bridges are critical components of lifeline systems that must remain functional without being severely damaged during earthquakes. Recently, researchers have carried out many studies on how the earthquake incidence angle affects the analysis results of bridges. In the literature, the earthquake incidence angle (θ) is considered using two different methods. In the first method, the bridge principal axes remain constant, and the ground motion components are rotated using linear transformation equations (Method 1). The ground motion components remain constant in the second method, and the bridge’s principal axes are rotated (Method 2). In Method 1, the acceleration values in the time series of the ground motion are modified by the linear transformation process. There is no interference with the earthquake ground motion records in Method 2. However, the most important difficulty with Method 2 is the necessity to reconstruct the bridge analytical model for each earthquake incidence angle. Within the scope of this study, the aim was to identify the method that will most efficiently reflect the incidence angle of the ground motion components in the nonlinear analysis of skewed highway bridges. In this context, analytical models of a highway bridge that consisted of prestressed concrete I-section beams and a continuous deck with different skew angles were created in OpenSees. Nonlinear response history analyses were performed for each incidence angle using two different methods. According to the analysis results, when several engineering demand parameters were considered, such as superstructure displacement that belonged to a joint at the bridge midpoint on the superstructure, force and curvature demands of the bridge piers, and pounding effect, the most effective method was investigated. Then, the aim was to identify the most unfavorable earthquake incidence angle for these parameters.