Multi-hazard effects of scour and earthquake for skewed highway bridges considering ground motion directionality

In literature, the earthquake incidence angle (θ) is taken into account using two different methods. In the first method, bridge principal axes are kept constant and ground motion components are rotated using linear transformation equations (Method-1). In the second method, the ground motion components are kept constant and the bridge principal axes are rotated (Method-2). The study aims to compare two methods and identify the most effective method in reflecting the effect of incidence angle of ground motion components to the nonlinear analysis of skew bridges. After deciding on the method, the most unfavorable earthquake incidence angle for various engineering demand parameters was determined. In the next stage, the variation of seismic demands of the bridge elements was examined due to the effect of the scour, which occurs around the substructure elements due to the erosive effect of water over time, especially in bridges built on stream beds. Two different scour cases can be observed around bridge piles, which are uniform and non-uniform scour cases. To reflect the critical ground motion angle in the analyses, horizontal ground motion components were rotated from 0° to 180° in 15° increments. Considering the nonlinear analyses results, it is inferred that the scour case is an important parameter that greatly affects the seismic demands of bridges. Additionally, there is no specific critical earthquake incidence angle for each demand parameter. Lastly, a suggestion is made to improve the Caltrans recommendation for considering the critical earthquake excitation angles to achieve the most unfavorable seismic demands imposed on bridges. Keywords: Ground motion incidence angle, Non-uniform scour, Residual displacement, Nonlinear response history analysis, Soil-structure interaction.