Vortex-induced vibration characteristics of twin-box girder section in long-span bridge: A numerical evaluation method

The vortex-induced vibration (VIV) characteristics of twin-box girders are critical in the design of long-span bridges. This study aims to investigate the VIV behavior of a twin-box girder section and to deepen the understanding of the mechanisms underlying VIV. A numerical approach that integrates both free and forced vibration analyses is developed to predict VIV performance. The VIV amplitude is evaluated using the free vibration method within the wind speed range identified by the forced vibration method. Comparisons with wind tunnel test results demonstrate the feasibility of this approach. Meanwhile, flow structure and aerodynamic characteristics of the twin-box girder were analyzed in relation to the VIV mechanism. The results show that flow restrictor plate could effectively suppress vertical VIV at a wind attack angle 0 degrees and reduce the VIV amplitude by 50% at +3 degrees wind attack angle. The central opening slot is identified as a significant factor in inducing VIV, as the upper and lower vortices interact with the airflow passing through the respective sections of the slot. The flow restrictor plates positioned at the upper section of the opening slot cause most upper vortices to shift downstream at wind attack angles of 0 degrees and +3 degrees. This shift results in minimal airflow reflux at the slot, which is crucial for optimizing VIV performance. At a wind attack angle of +3 degrees, the vortices at the lower part of the slot persist, albeit with reduced size. These changes in vortex behavior underscore the sensitivity of vortex formation to variations in wind attack angles.