Dynamic Response of Sea-Crossing Rail-cum-Road Cable-Stayed Bridge Influenced by Random Wind—Wave—Undercurrent Coupling

Sea-crossing bridges are affected by random wind—wave—undercurrent coupling loads, due to the complex marine environment. The dynamic response of long-span Rail-cum-Road cable-stayed bridges is particularly severe under their influence, potentially leading to safety problems. In this paper, a fluid-structure separation solution method is implemented using Ansys—Midas co-simulation, in order to solve the above issues effectively while using less computational resources. The feasibility of the method is verified by comparing the tower top displacement response with relevant experimental data. From time and frequency domain perspectives, the displacement and acceleration responses of the sea-crossing Rail-cum-Road cable-stayed bridge influenced by wave-only, wind—wave, and wind—wave—undercurrent coupling are comparatively studied. The results indicate that the displacement and acceleration of the front bearing platform top are more significant than those of the rear bearing platform. The dominant frequency under wind—wave—undercurrent coupling is close to the natural vibration frequencies of several bridge modes, such that wind—wave—undercurrent coupling is more likely to cause a resonance effect in the bridge. Compared with the wave-only and wind—wave coupling, wind—wave—undercurrent coupling can excite bridges to produce larger displacement and acceleration responses: at the middle of the main girder span, compared with the wave-only case, the maximum displacement in the transverse bridge direction increases by 23.58% and 46.95% in the wind—wave and wind—wave—undercurrent coupling cases, respectively; at the tower top, the variation in the amplitude of the displacement and acceleration responses of wind—wave and wind—wave—undercurrent coupling are larger than those in the wave-only case, where the acceleration change amplitude of the tower top is from −0.93 to 0.86 m/s2 in the wave-only case, from −2.2 to 2.1 m/s2 under wind—wave coupling effect, and from −2.6 to 2.65 m/s2 under wind—wave—undercurrent coupling effect, indicating that the tower top is mainly affected by wind loads, but wave and undercurrent loads cannot be neglected.