Aerodynamic mechanism of triggering and suppression of vortex-induced vibrations for a triple-box girder

With the objective of exploring the aerodynamic mechanism of triggering and suppression of vortex-induced vibration (VIV) for a triple-box girder, wind tunnel tests involving both static and dynamic pressure measurements, as well as CFD simulation for flow visualization were carried out on a bare girder. Both vortex-induced vibrations and surface pressures were obtained from static and dynamic sectional model tests for three typical wind incidence angles, namely alpha = 0 degrees, +3 degrees, and - 3 degrees. Results indicated that vortices shed regularly from the downwind sides of both windward box and middle box, then impinged on the upwind sides of middle box and leeward box respectively, resulting in prominent fluctuating pressures here, which was likely to render the triplebox girder more susceptible to VIV. Specifically, fluctuating lift of middle box was the main trigger of VIV at wind incidence angle alpha = +3 degrees, while that of leeward box was the main trigger at alpha = 0 degrees and - 3 degrees. The regular vortex shedding and impinging process could be effectively suppressed by the grid plates over girder slots, which was favorable to VIV mitigation. When VIV occurred, self-excited force became the main component of the fluctuating force, and it could be the major driver of the large-amplitude oscillation.