Effects Of Vibration Regime On Flow Field Characteristics Of Twin-box Girder

The super-span bridge has the characteristics of relatively low mass,low stiffness and low damping ratio,which makes it easy to generate wind-induced vibration.Therefore,the wind-resistant design of the bridge plays a key role in the design stage of the long-span bridge.The cross-section of the main girder with a split double box is a measure to improve the flutter stability of super-long span bridges.The Separated double box girder increases the critical wind speed of bridge flutter,and the increased intermediate gap also results in a more complicated flow field around the main beam,and it is easy to lead to vortex-induced vibration.The vibration mechanism refers to the form of constraints on the model,and the form of the constraints has a great influence on the flow field around the model.In this paper,the influence of vibration mechanism on the flow field characteristics of long-span separated double-box girder is studied based on wind tunnel test.Firstly,with the separated double-box girder segment model being fixed and elastically suspended wind tunnel being tested,the vortex-induced vibration characteristics of the model are deeply analyzed,and the surface wind pressure,along the inflow direction of the main girder segment model without an auxiliary structure under different vibration mechanisms,as well as the variation law of the distribution characteristics of flow field structure in the whole process of vortex-induced vibration is analyzed,thus revealing the influence of different vibration mechanisms on the flow law of the separated double-box beam around the flow field and analyzing the vibration mechanism and vibration amplitude versus pressure coefficient and flow field pulsation RMS(the influence of the root mean square value of the pressure).The influence of the vibration mechanism on the position of the separation point is also studied,and therefore the judgment basis for whether the structure may generate vortex-induced vibration is obtained.Secondly,the influence of vibration mechanism on the correlation of the separation of the double box girder model is studied.The surface pressure extension correlation and the lift correlation of the lift double box girder model under different vibration mechanisms are analyzed.With this analysis,the variation trend of the surface pressure extension correlation along the inflow direction under different vibration mechanisms is obtained.The relationship between the on-line correlation of the model surface pressure and the variation of the wind speed under the different mechanisms of vibration are analyzed.The comparison of the variation law of the surface correlation of the surface pressure under different vibration mechanisms is carried out.The relationship between the change trend of the lift and the correlation of the vortex vibration amplitude in the vortex-locked zone is analyzed in depth,while the influence of vibration mechanism on the lift coefficient and pressure cross-correlation of the upper and lower surfaces is analyzed.