Numerical study of pile group effect on the hydrodynamic force on a pile of sea-crossing bridges during earthquakes

Pile group effect is crucial for correct estimation of the hydrodynamic force on a pile within a pile-group foundation of sea-crossing bridge during earthquakes unlike the case of single isolated pile. A numerical calculation model considering fluid-structure interaction under the combined loads of earthquakes, waves and currents is established, based on the second development on ANSYS software. A detailed analysis of pile group effect in the earthquake-induced oscillatory flow field, is carried out by the presented method that is validated in advance. Pile group effect in the earthquake-current combined flow field, as well as in the earthquake-wave combined flow field are further discussed. Pile group effect has almost disappeared when relative spacing S/D = 4.5 and all piles behave like a single isolated pile in terms of earthquake-induced hydrodynamic forces, yet, in the coexistence field, the range of S/D influencing pile group effect has been expanded due to the presence of current and wave. For a sea-crossing bridge foundation, Pile group effect coefficient K is equal to 0.69, implying noticeable interference effects, and results show the hydrodynamic force on corner pile is greater than that on centre pile, strengthening section reinforcement pertinently so as to improve overall seismic performance.