Dynamic Response Analysis of Deep-water Piers Under Coupled Earthquake-wave Action Considering Phase Difference

Cross-sea deep-water piers are often subjected to wave action. Because this cannot be ignored, wave force should be considered in deep-water pier design. During an earthquake, the wave field near piers is disturbed by the dynamic water pressure, and the wave action is also affected. Therefore, coupling interaction between an earthquake and wave should be considered in dynamic response analysis. However, when an earthquake begins, the phase of the seismic excitation at the bottom of piers can be simply regarded as 0, whereas the phase of the wave on the surface of piers may vary from 0 to 2π. The phase difference between the earthquake and wave will directly affect the magnitude of wave action and in turn affect the coupled earthquake-wave action. Therefore, studying the dynamic coupling effect of earthquakes and waves on deep-water piers and considering the influence of phase difference on the dynamic responses of piers are of great significance. In this study, a refined model of composite piers and potential fluid element model of water bodies near piers were established using the finite element analysis software ADINA to simulate fluid-structure interaction. The dynamic responses of piers under independent earthquake action, independent wave action, and coupled earthquake-wave action were analyzed, and the differences in ground motion, wave height, and phase difference between the earthquake and wave were considered. Results show that the coupling interaction between an earthquake and wave must not be ignored and its influence on total hydrodynamic pressure is approximately 15%. The phase difference between an earthquake and wave has a significant effect on the dynamic responses of piers. When the phase difference varies between 0 and 2π, the maximum response amplitude varies nearly 54%. The most unfavorable phase difference is closely related to the frequency of earthquake excitation, natural frequency under water, and pier structural type. A method for identifying the most unfavorable phase difference using MATLAB software and a simplified method for calculating the maximum coupled dynamic responses of piers using a coupling coefficient were proposed, which allow for convenient application to actual engineering design. © 2021, Editorial Department of China Journal of Highway and Transport. All right reserved.