Vortex-Induced Vibration Performance And Control Of Twin-box Girder

Twin-box girder is widely used in the design of large-span bridge due to its well flutter stability,but the vortex-induced vibration(VIV)of twin-box girder is poor.The useful VIV control method of twin-box girder is less.Wind tunnel test and CFD method were taken to study the VIV characteristics and VIV control method of twin-box girder.Double central stabilizer is used as a new kind of twin-box girder VIV control method.A twin-box girder,which has torsional VIV,is tested to obtain surface mean pressure coefficient and the surface pressure predominant frequency in different state by surface pressure measurement and vibration measurement of wind tunnel test.By analyzing surface mean pressure coefficient,it is found that the surface mean pressure coefficient at different region of twin-box girder changes differently with wind velocity in restrained conditions.In the torsional VIV lock-on region,the surface mean pressure coefficient is mainly affected by the VIV stage,and the trend of surface mean pressure coefficient changing with wind speed shows a high consistency.By analyzing the distribution of surface pressure predominant frequency,it is found that the vortex shedding effect in the gap of twin-box girder is the necessary condition of the VIV of twin-box girder.The vortex shedding affecting region shrinks to the gap with the wind speed increasing in the VIV lock-on region.When the wind speed is out of VIV lock-on region,the surface pressure predominant frequency around the gap increases,the VIV of twin-box girder disappears.Sectional model wind tunnel test of the twin-box girder with different mass parameters and damping parameters was carried out,and the relationship between the vortex response of the twin-box girder with the change of the mass and damping parameters was obtained.It is found that different VIV lock-on regions have different sensitivity to Sc number.Using different aerodynamic shape of twin-box girder to do section model wind tunnel test,and get the VIV response of each section model.And the corresponding time-averaged streamline is obtained by CFD method.There is a corresponding relationship between the VIV response and the vortex size and distribution in the time-averaged streamline.It is found that the vortex distribution in the time-averaged streamline is related to the maximum VIV amplitude.According to the flow filed analysis,the development of vortex is obtained.The attachment and detachment at downwind box of vortex from the gap contributes to the VIV of twin-box girder.Double central stabilizer can make vortex in the gap depress,and reduce the size of vortex to control the VIV amplitude from the flow field analysis.It is recommended that the spacing of double central stabilizer is about one-fourth of the gap width,and the height is within the range of one-third to one-half the girder depth.