Wave overtopping effects and load characteristics on bridge substructures

Wave overtopping effects during wave-bridge interaction, akin to green water events on structural decks, pose significant threats to structural integrity and safety, potentially leading to localized damage or even permanent failure. Despite their critical implications, nonlinear flow behaviors and load characteristics during such events remain inadequately understood, and efficient load prediction methods are lacking. In this study, wave overtopping effects on a pier-pile group foundation, a common substructure of sea-crossing bridges, are comprehensively investigated in a 1:50 scale laboratory experiment. Experimental results reveal complex flow behaviors of significant relevance to structural safety. Specifically, low-aeration impacts on the pier front wall are induced by accelerating overtopping flows. Moreover, high-velocity flows from both pier sides are observed to collide on the rear top wall of the pile cap, subsequently evolving into a wall of water that creates reverse secondary impacts on the pier. During water outflow, transient high pressures on the vertical wall of the pile cap are caused by small jets and splashing water. Although high-frequency slamming forces are contributed to by these flow behaviors, they minimally influence global forces, which are predominantly governed by quasi-static forces from the pile cap and pile group. Based on the experimental data, novel methods for predicting impact pressures and global forces during wave overtopping are finally proposed, and their accuracy and limitations are also discussed. This work enhances the physical understanding of wave overtopping effects during wave-bridge interaction and aims to support the design of sea-crossing bridges and other marine structures.