Study on characteristics and calculation method of hydrodynamic force on pile group under earthquake

The substructure of the deep-water bridge is ordinarily composed of pile group, pile cap and bridge pier. The calculation method of the hydrodynamic force on pile group under earthquakes receives few concerns. It's difficult to deduce the analytical calculation method of hydrodynamic force directly because the flow field induced by synchronously vibrating piles is considerably complicated. Two assumptions, i.e. the change of influence of column C-j (j 6 not equal i) on column C-i caused by the existence of other columns is ignorable and the influences on hydrodynamic force of a column caused by other columns could be superposed approximately, are put forward. Then numerical software ANSYS FLUENT is employed to validate the assumptions. Based on the hydrodynamic force calculation method of twin columns, the hydrodynamic force calculation method of pile group is proposed. Results show for those pile groups composed of dozens of piles, the added mass modified coefficients are smaller and can be ignored. Application study shows the calculation method proposed in this study not only precise enough but also convenient and efficient for real practice. Also the characteristics and generation mechanism of hydrodynamic force on columns of three-column group are analyzed elaborately.