Experimental study on characteristics of vortex-induced vibration of a twin-box girder and damping effects

Abstract

To investigate the characteristics of vortex-induced vibration (VIV) of the twin-box girder, we carried out the VIV wind tunnel tests. The VIV of the twin-box girder occurs in the range of 4.680≤Ur≤6.113, with the maximum dimensionless VIV displacement RMS(y)/D=0.03308 at reduced velocity at Ur=5.949. It is interesting that the VIV suddenly disappears at Ur=6.276 at the loading stage, and the large amplitude VIV does not occur at the unloading stage, which indicates that the vibration trajectory with the variation of reduced wind velocity shows significant asymmetry characteristic. In the lock-in region, as the aerodynamic lift force increases, both the phase lag and the VIV displacement show an increasing tendency with the reduced velocity. Flow visualization results show that strong alternately shedding vortex generates around the gap during the VIV. Under the effects of the vortex in the gap, the size of the separation bubble increases with the increase of vibration amplitude, and the wake width becomes wider. As the damping ratio increases, the amplitude of VIV displacement shows a decreasing tendency, the lock-in region becomes narrower and the reduced velocity corresponding to the max VIV displacement decreases. Moreover, the maximum RMS displacement of vertical VIV decays exponentially as the damping ratio increases.