Tsunamis and storm surges can wash away bridge girders. It causes severe traffic disruption. To simulate the movement of bridge girders caused by a solitary wave, it is essential to calculate not only the gas-liquid two-phase fluid interactions but also the contact and friction with bridge piers. This paper develops a new fluid–structure interaction (FSI) model to simulate bridge girder washout by combining the CFD software OpenFOAM and the physics engine Bullet. To validate the developed model, three model experiments were conducted in which solitary waves were applied to a bridge girder: one force measuring experiment and two motion measuring experiments. The force measuring experiment was conducted to measure the fluid force, and motion measuring experiments were conducted to observe changes in the washout behavior of bridge girders due to different pier geometries. In the force measuring experiment, the model reproduced the increase in vertical force associated with the increase in pressure in the air pockets under the bridge girders. In motion measuring experiments, the model reproduced the variation in displacement due to different bridge girder geometries, while the shear key significantly reduced the amount of displacement.