This paper presents an experimental program performed to study the effect of fluid-structure interaction on the modal dynamic response of water-surrounded slender bridge pier with pile foundation. A reduced scale slender bridge pier specimen is built and tested through forced vibration method. The vibration periods of the first four lateral modes, including the first two modes along x-axis and the first two modes along y-axis, are measured based on the specimen submerged by 16 levels of water and designated with 4 levels of tip mass. Three-dimensional (3D) finite-element models are established for the tested water-pier system and analyzed under various combined cases of water level and tip mass. Percentage increases of vibration periods with respect to dry vibration periods (i.e., vibration periods of the specimen without water) are determined as a function of water level and tip mass to evaluate the effect of fluid-structure interaction. The numerical results are successfully validated against the recorded test data. Based on the validated models, the modal hydrodynamic pressures are calculated to characterize the 3D distribution of hydrodynamic loads on the pier systems. The research provides a better illumination into the effect of fluid-structure interaction on the modal dynamic response of deepwater bridges.

This article presents an experiment program conducted to study the modal dynamic response of hollow bridge pier with pile foundation submerged in water. The forced vibration method was applied on a specimen designated with four levels of tip mass; and the dynamic characteristics of the first four lateral vibration modes of the specimen, including the first two modes along the x‐axis and the first two modes along the y‐axis, were tested for three different cases where the specimen contacts with only outer water, only inner water, and both outer and inner water, respectively. Finite element models were established using potential‐based fluid elements in accordance with the three different cases. The effects of fluid‐structure interaction on the dynamic characteristics of the first four lateral modes of the specimen were then investigated through numerical simulations, and the finite element models were verified by validating numerical results against the experimental data. Based on the verified models, hydrodynamic added mass (HAM) and modal hydrodynamic added mass (MHAM) along the x‐axis and y‐axis of the specimen, induced by fluid‐structure interaction, were studied with respect to the three cases. According to the distribution of modal acceleration and hydrodynamic pressure along the pier body, hydrodynamic added mass (HAM) distribution along the pier body was analyzed, and a simplified analytical model which equals the original fluid‐structure numerical model was proposed to determine the dynamic characteristics of hollow bridge piers submerged in water. The research provides a better understanding of the effect of fluid‐structure interaction on the modal dynamic response of deep‐water bridges with hollow piers.