Vortex-induced Vibration Performance And Flow Field Of Twin-box Girder

Compared with the traditional monolithic box girder,the fluttering stability of the separated twin-box girder is superior,and the critical wind speed of the flutter is higher,which has been more and more widely used.However,due to the increase of the central slot,the flow field around the twin-box girder is more complicated and the vortex-induced vibration performance deteriorates,which affects the driving comfort and even leads to the deterioration of the fatigue performance.Therefore,it is necessary to study the vortex vibration performance of twin-box girder.research.Based on wind tunnel test and particle imaging technology,this paper takes a large span suspension bridge as the research object and studies the vortexinduced vibration performance,vortex-induced vibration suppression,and the flow field characteristics of the twin-box girder.First,a wind tunnel test is performed on a flexible segment model with a geometric scale ratio of 1:70.The vortex-induced vibration response of the twin-box girder model at five attack angles of 0°,±3°,and ±5° is measured.The variation law of the amplitude of the vortex of the twin-box girder with the wind speed determines the wind speed lock interval and amplitude when the twin-box girder vortex occurs,and compares it with the allowable value of the specification.Second,a series of vibration suppression measures were applied to the twin-box girder model,and its vortex response is measured to determine the effectiveness of the vortex suppression measures.Through a series of experimental studies,it is found that setting the grille at the center slot of the twin-box girder can effectively suppress the vortex-induced vibration of the twin-box girder,but the effect of vibration suppression depends on the design parameters of the grille.Thirdly,the influence of grid design parameters(flux rate,strip width ratio,grid type,and installation position)on the suppression effect of vortex-induced vibration is systematically studied.It is found that the peak value of the vortex-induced vibration of double-girder bridges is increased with the increase of ventilation rate.The amplitude decreases first and then increases.There is an optimal range of ventilation rate,so that the vibration suppression effect of the grille is best.The optimum ventilation rate range is 42%-67%.At this time,the vertical vortex vibration of the twin-box girder is completely suppressed.There is an optimum ratio of the width to the width of the grid,so that the grille has the best anti-vibration effect.The optimum ratio of the width to the width is 0.084-0.167.The uniform arrangement of the grid plate is better than the non-uniform arrangement and the vibration suppression effect is better.The grid installed on the upper side of the central gap of the twinbox girder is better than the lower side to suppress the vortex-induced vibration.Fourthly,particle imaging technology is used to measure the flow field information around the twin-box girder model.The influence of the installation grid on the flow field of the twin-box girder is studied,and the mechanism of the grille suppressing the vortex-induced vibration of the twinbox girder is revealed.The main cause of the vortex-induced vibration of the twin-box girder is closely related to the large-scale vortex of the tail of the upper box girder.By appropriately selecting the design parameters of the grid plate,the generation of large-scale vortices can be eliminated,thereby suppressing the vortex-induced vibration of the main beam.