Influence of Central Buckle on Flutter Stability of Long-span Suspension Bridge

To investigate the effects of central buckles on the flutter stability of long-span suspension bridges, the Aizhai Bridge in China was selected as the engineering background. Based on a refined spatial-truss-girder model and according to the principle of stiffness equivalence of the main girder in all directions, an equivalent-single-girder finite element model was firstly established by using the displacement method of a cantilever beam. Subsequently, four different connection options between the main cable and the girder near the mid-span position, namely, a short suspender, one pair of flexible central buckles, three pairs of flexible central buckles and one pair of rigid central buckles, were considered and their effects on the dynamic characteristics of long span suspension bridges were studied. Then, based on the flutter derivatives obtained from wind tunnel tests, the time domain formulations of self-excited forces in the girder section, expressed in terms of convolution integrals of impulse response functions, were obtained using a nonlinear least square fitting method. Based on APDL (ANSYS Parametric Design Language) offered by ANSYS, a time-domain flutter analysis was realized. Finally, 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 asymmetric lateral bending mode and asymmetric torsion mode than that of symmetric ones. The rigid central buckle can largely increase the frequency of asymmetric torsion mode. The central buckles have negligible impact on the critical flutter velocity because the flutter mode shape of the Aizhai Bridge is coupled with the symmetric vertical bending mode shape and the symmetric torsion mode shape. However, it has a certain impact on the flutter frequency and the three-dimensional flutter states of the bridge, which benefits the flutter stability. In addition, it is found that the phenomenon of complex beat vibration (called intermittent flutter phenomenon) appeared when the structural damping was very low, because the flutter frequency falls in an area where the natural frequency distribution is very dense. © 2021, Editorial Department of Journal of Hunan University. All right reserved.