Multi-mode vortex-induced vibration of a long-span bridge under non-uniform flows

An increasing number of modern long-span bridges have been built in complex valley terrain, and the influence of non-uniform flows on the vortex-induced vibrations (VIVs) of bridges should be considered. Therefore, this study investigated the multi-mode VIVs of long-span bridges in both the completed bridge stage and erection stage using a taut-strip model under a uniform flow and two types of non-uniform flow. The non-uniform flows were generated by adjusting spires (both their separation distance and shapes) in wind tunnel. The two non-uniform flows were repre-sented by the linear and parabolic wind velocity flow distributions. The characteristics of the vibration responses and wake flows, mechanism of multi-mode VIVs, and aerodynamic differ-ences between different stages and under different incoming flows were discussed. The results indicated that the occurrence of multi-mode VIVs arose from a wake frequency difference covering two or more modal frequencies owing to variations in the wind profile. The non-uniform flows disturb the regular vortices in the wake due to the variable wind velocity and higher tur-bulence intensity, leading to suppression of the VIV response.