Equivalent lateral load pattern on elevated pile-cap bridge subjected to vessel collisions

To accurately estimate the collision-induced demand of bridge structures, the equivalent lateral barge impact load was investigated from the view of the load pattern for the elevated pile-cap bridge that has been extensively used in Chinese navigable waters. By considering the dynamic characteristics of the elevated pile-cap foundation, it was simplified into two degree-of-freedom (2-DOF) system in the development of the equivalent lateral barge impact load pattern. Based on the vibration modes of the 2-DOF model, the barge shock spectrum and the modal combination rule, an innovative method was derived to determine equivalent loads on the bridge subjected to barge collisions. The developed method was applied to the practical example and compared with the code-prescribed static method. The results show that there are significant differences between the mode-based equivalent load pattern and the concentrated force of single point commonly recommended by the design specification; the accuracy of the code-prescribed method is very low and its error is still large if the magnitude of the barge-impact load is simply increased but the load pattern is not adjusted, indicating that the load pattern plays a crucial role in determining the demand and capacity of bridge structures under barge impacts; the structural response results obtained from the proposed method are in good agreement with the dynamic results, and its accuracy is not sensitive to the mass ratio and the pier to pile-group stiffness ratio. © 2016, Editorial Department of China Journal of Highway and Transport. All right reserved.