Study of central buckle effects on flutter of long-span suspension bridges

To investigate the effects of central buckles on the dynamic behavior and flutter stability of long-span suspension bridges, four different connection options between the main cable and the girder near the mid-span position of the Aizhai Bridge were studied. Based on the flutter derivatives obtained from wind tunnel tests, formulations of self-excited forces in the time domain were obtained using a nonlinear least square fitting method and a time-domain flutter analysis was realized. Subsequently, the influences of the central buckles on the critical flutter velocity, flutter frequency, and three-dimensional flutter states of the bridge were investigated. The results show that the central buckles can significantly increase the frequency of the longitudinal floating mode of the bridge and have greater influence on the frequencies of the asymmetric lateral bending mode and asymmetric torsion mode than on that of the symmetric ones. As such, the central buckles have small impact on the critical flutter velocity due to that the flutter mode of the Aizhai Bridge was essentially the symmetric torsion mode coupled with the symmetric vertical mode. However, the central buckles have certain impact on the flutter mode and the three-dimensional flutter states of the bridge. In addition, it is found that the phenomenon of complex beat vibrations (called intermittent flutter phenomenon) appeared in the flutter state of the bridge when the structural damping is 0 or very low.