Vortex-induced vibration analysis of long-span bridges with twin-box decks under non-uniformly distributed turbulent winds

With the increase of span length, long-span bridges become more flexible and susceptible to vortex-induced vibrations (VIV). Large-amplitude VIV may cause fatigue damage to structural components, and therefore accurate predictions of vortex-induced responses (VIR) are important. This paper proposes a mode-by-mode VIV analysis method for long-span bridges with twin-box decks under non-uniformly distributed turbulent winds. A semi-empirical model of vortex-induced forces (VIF), developed by the authors and validated by direct force measurements on an elastically-mounted twin-box section model under turbulent winds, is embedded in the VIV analysis method. The proposed analysis method is then used to analyze the VIV of a real long-span suspension bridge of a twin-box deck. The computed VIR of the prototype-bridge is finally compared with the VIR measured on-site by a structural heath monitoring system installed in the bridge. The comparative results show that the proposed VIV analysis method can be used to predict the VIR of long-span bridges with twin-box decks. Further studies also show that the non-uniform distribution of mean wind speed reduces the VIV of the bridge. Turbulence also diminishes the VIV of the bridge, and the reduction effect is larger on lower-order modes of vibration than on higher-order modes of vibration.