Modal Analysis of the Saint-Bachi Suspension Aqueduct Bridge Considering Fluid–Structure Interaction

Abstract

The aim of this paper is to reveal the unique dynamic characteristics of the Saint-Bachi suspension pipeline bridge with fluid–structure interaction. With commercial software, a three-dimensional finite-element (FE) model of this bridge is developed to simulate its dynamic properties. The solid and fluid elements are, respectively, applied to model the structural members (pipe girder, cables, and portal frames) of the bridge and the water in the pipe girder. The dry (without fluid) and wet (with fluid) modes of the suspension pipeline bridge are, respectively, calculated and compared. The dry modes are fundamentally the same as those of the ordinary highway suspension bridges. The number of wet modes has been greatly increased due to the interaction between sloshing water and structure. According to the oscillation phases of sloshing fluid and pipe girder, the wet modes can be divided into the in-phase, out-of-phase, and no-sloshing modes. The in-phase and out-of-phase modes represent the synchronous and unsynchronous motions of pipe girder and fluid, respectively. The no-sloshing mode denotes a pure girder bending vibration without water sloshing. The in-phase (synchronous) frequencies are decreased with increased fluid depth. The out-of-phase (unsynchronous) frequencies might be increased or decreased with increased fluid depth. The (local) wet frequencies of pylons and cables may increase with the increment of water depth due to increased tension force of the cables.