Wake-Induced Vibrations of the Hangers of the Xihoumen Bridge

Large-amplitude wind-induced vibrations of hangers have been observed on the Xihoumen Bridge, and the excitation mechanism is still unknown at present. In the present study, the mechanism of the wind-induced vibration of the hangers of the Xihoumen Bridge was investigated based on field measurements, wind tunnel tests, and theoretical analyses. First, a series of field measurements on the No. 2 hanger of the Xihoumen Bridge were carried out. It is shown that the oscillation amplitudes of the downstream cables were significantly larger than those of the upstream cables under two different wind yaw angles. Second, a three-dimensional aeroelastic test model of the hanger was designed and manufactured with the No. 2 hanger of the Xihoumen Bridge as a prototype, and a series of wind tunnel tests were carried out to obtain the responses of the cables. The results show that large-amplitude oscillations of the downstream cables can be reproduced by using wind tunnel tests under the same wind directions as the field measurements, whereas the upstream cables keep calm in the meantime. This indicates that wake-induced vibration (WIV) should be the reason for the hanger vibration in the Xihoumen Bridge. In the wind tunnel tests, the effects of the structural damping and spacers on the WIV of the hanger were examined. It is shown that the spacers are significantly effective to reduce the WIV of the hanger. However, it seems that the oscillation amplitude of the hanger cannot be effectively mitigated by increasing structural damping. Finally, the WIV of the No. 2 hanger of the Xihoumen Bridge under the wind yaw angle alpha = 40 degrees was theoretically analyzed. The results show that the main characteristics of the hanger vibration observed in the field measurements and wind tunnel tests were successfully reproduced by theoretical analyses. This indicates once again that WIV is the mechanism for the hanger vibration of the Xihoumen Bridge.