THEORETICAL INVESTIGATION FOR THE EFFECTIVENESS OF THE DAMPERS INSTALLED BETWEEN THE HANGERS OF SUSPENSION BRIDGES

The large amplitude vibrations of hangers on several suspension bridges all over the world were observed in recent years. Some effective countermeasures should be adopted to mitigate this type of vibration. In this paper, the effectiveness of the dampers to the vibrations of hangers is investigated by using theoretical analyses. First, the equations governing the in-plane motion of a twin-hanger-damper system are derived by neglecting the stiffness of hangers. Second, the finite difference method (FDM) is utilized to numerically solve the equations, and the natural frequency, mode shape and damping ratio are obtained. Third, taking a hanger on Xihoumen Bridge as engineering background, the effectiveness of dampers to mitigate the hanger's vibration is carefully investigated. The results show that the damping ratio of the synchronous mode of the two strands does not increase by installing dampers between the two strands. However, the stiffness for single strand could be enhanced by uniformly installing dampers between the two strands because the effective length of the single strand becomes shorter. It is benefit for mitigating wind induced vibration of hangers. The authors suggest that rigid spacers are suitable for reducing the relative oscillation between the strands.