Optimization of Damped Outriggers for Maximizing Multimode Damping of Long-span Bridges for Vibration Suppression

Characterized by large flexibility and low damping, long-span cablesupported bridges are subjected to wind-induced vibrations. Aerodynamic countermeasures might be no longer sufficient for vibration mitigation of such bridges. Therefore, it is important to install dampers on bridges for supplementing damping. This study focuses on a novel strategy by using damped outriggers to control the rotation of the bridge deck at the junction points between the girder and the bridge tower or pier. Specifically, a vertical rigid arm is installed on the girder near the junction, and the end of the rigid arm is connected to the bridge tower through horizontal dampers. Through the damped outriggers, the angular displacement of the girders can be transformed into the linear displacement at the end of the rigid arm, and then the energy can be consumed by the horizontal dampers to suppress the vibration. Subsequently, a general design method for adding damped outriggers to long-span cable-supported bridges is proposed. At last, the Xihoumen Bridge with a main span of 1650 m is taken as an example for detailed dynamic analyses. A finite element model of the bridge with damped outriggers is established. The static analysis and eigen analysis are then carried out. The damped outriggers are installed at multiple positions, and the optimal damping coefficients of dampers are discussed for multimode vibration mitigation so that the damping ratio of modes in which vortex-induced vibration (VIV) occur are relatively large. The results show that through the proposed optimization method, the strategy can provide relatively large damping ratio for VIV modes, which is of great practical significance.