In this paper, a 2D numerical model for wave-girder interaction was proposed to estimate the maximum wave forces on the box girder of a coastal bridge under extreme wave conditions. The Reynolds Averaged Navier-Stokes (RANS) equations were applied to simulate water wave motion and the Volume of Fluid (VOF) method was used to track the free surface. In this study, the developed 2D numerical model was validated by first comparing with experimental data. Then, a set of parametric studies was conducted to examine the effects of the wave heights, wave periods, water depths and submerged coefficients on the wave force on the box girder under extreme wave conditions. Finally, a function to predict the extreme wave-induced forces on the box girder under various wave conditions was proposed for engineering practice.

In this study, a three-dimensional numerical model for a pile-cap system of an offshore bridge is developed to examine the pile group effect on wave force of pile with different arrangements of the pile group with a pile-cap system. In the present model, the Reynolds-averaged Navier-Stokes equation is taken as the governing equation for wave motion, while the volume of fluid method is used to trace the free water surface. Based on the present model, a set of analysis was conducted to examine the influence of the pile-cap system on the pile group effect, including the arrangement of the pile group, the submerged depth of the bridge cap, and the existence of the cap. Numerical examples show that the present model overall agreed well with the previous experimental data. The existence of the cap and submerged coefficient of the cap have a significant influence on the pile group effect coefficient. During the study of the pile group effect on the wave force of a pile with a pile-cap system of an offshore bridge, the influence of the existence of the cap on the pile group effect needs to be considered.