Research On Correlation Characteristics Of Vortex Induced Vibration Of Variable Cross-section Steel Box Girder Bridge

As the span of modern continuous girder bridges increases and the materials used are mostly steel,the structure becomes flexible and the damping becomes smaller.The wind resistance of continuous steel box girder bridges has become a factor that must be considered in bridge design.Because long-span continuous steel box girder bridges often adopt the form of variable cross-sections with heightened pier tops,the cross section is more complicated than that of a single flat steel box girder.In this paper,the cross-sectional model of three different web heights of a variable-section continuous steel box girder bridge span is used as the research object.The wind tunnel test and numerical simulation are used to analyze the cross-section steel box girder under different web heights.The vortex-induced vibration characteristics and static aerodynamic characteristics of the cross section were studied.First,a section model wind tunnel test was carried out on the cross section of the flat steel box girder in the mid-span.By changing the vibration mechanism of the model,the model was subjected to the wind tunnel test under the fixed state and the vibrating state to study the different vibration mechanisms.The distribution law of cross-section wind pressure,and explore the influence of vibration mechanism on the flow field characteristics of the box girder structure;on this basis,by increasing the web to simulate the cross-sectional form of the cross section of the quadrant and fulcrum of the variable cross-section steel box girder,to The influence of web height changes on the characteristics of the flow field around the steel box girder was studied,and the effects of web height and beam bottom linear changes on the static and aerodynamic three-component force coefficients of variable cross-section continuous steel box girder bridges were analyzed in depth by numerical simulation Finally,in order to study the influencing factors of box beam spanwise correlation,by changing the vibration mechanism of the model,increasing the height of the web,changing the reduced wind speed and other control variables to analyze the change law of the model’s spanning correlation under different working conditions,In order to explore the influence of vibration mechanism,box girder shape,vortex vibration amplitude and other factors on the direction correlation,and verify the effects of aerodynamic measures and mechanical measures by experiments,reasonable vortex vibration suppression measures are proposed.The study found that the flow field and vortex-induced vibration-related characteristics of different cross-section continuous steel box girder bridges are greatly affected by the vibration mechanism and web height;the wind pressure and aerodynamic direction of the different cross-section continuous steel box girder bridges are related The performance isgreatly affected by factors such as turbulence,vibration mechanism,reduced wind speed and vortex amplitude,and web height,and the correlation coefficient of wind pressure spread in the vortex lock interval shows that the vortex amplitude rises and the vortex vibration The peak amplitude stage is obviously higher than the trend of other vortex stages,in which the amplitude correlation coefficient in the rising stage is the largest.When the bottom line of the variable-section steel box girder is an oblique line with a larger angle from the horizontal line or a parabola,the corresponding calculation model beam bottom line should be completely consistent with the real bridge during numerical simulation to improve engineering accuracy.Through the experiment of vibration suppression measures on the segment models at different positions,it is found that the aerodynamic vibration suppression measures that are only suitable for flat steel box girder are not suitable for variable cross section steel box girder bridges.The mechanical measures to increase the damping ratio can be achieved Good vibration suppression effect.In this paper,through preliminary exploration of the relevant flow field characteristics at the critical position of the cross-section of the steel box girder with variable cross-section,it is of great value for the further study of the three-dimensional wind pressure change and vortex vibration characteristics of the variable cross-section bridge.On the basis of previous scholars,through the discussion and verification of the influencing factors of the span correlation,and the influence law of the change of the shape of the bridge cross section on the model span correlation is studied.It is of great significance to accurately predict the vortex amplitude of the main beam.Proposed vortex vibration suppression measures suitable for variable cross-section steel box girder bridges have important reference value for practical engineering.