Damping Effects of Cable Dampers on Girder Vibrations of Cable-Stayed Bridges

Abstract

Cables and the girder of long-span cable-supported bridges are subjected to problematic vibrations (e.g., vortex-induced vibrations), owing to low structural vibration frequency and damping. It is a common practice to install dampers between cables and the girder to suppress cable vibrations in cable-stayed bridges. The attainable cable damping has been the focus of a number of previous studies assuming the bridge girder as a rigid support of the dampers. The damping effects of those cable dampers on bridge girder vibration have not been studied, while it has been observed that during (quasi-static or dynamic) bridge girder deformation cable dampers are deformed considerably in long-span cable-stayed bridges. Therefore, it is of interest to appreciate the damping effects of cable dampers on girder vibrations. Besides, vibration mitigation of bridge girder is also of practical significance. For this purpose, a finite element model (FEM) of an existing long-span bridge—the Sutong Bridge that is the first cable-stayed bridge in the world with a main span over 1000 m—is used for damping analyses. Particularly, the cables are divided into a number of link elements and cable dampers are included in the FEM. By eigenanalysis of the full model, damping of the structural modes dominated by girder vibrations is obtained with respect to the damping coefficients of the cable dampers. The variation of the damping ratio for varying damping coefficients is demonstrated and discussed. It is found that the cable dampers can increase the damping of the bridge girder. The results are useful for cable damper design considering both their damping effects on cables and bridge girders.