Experimental Study On Aerodynamic Characteristics Of Twin Bluff Box Girders With Variable Cross Section

In recent years,with the increase of traffic volume,twin box bluff girders with variable cross section have been used more and more because of its good driving conditions.Because of the small spacing,there are aerodynamic interference effects between the twin box bluff girders with variable cross section under the action of incoming wind,and the aerodynamic characteristics are different from those of the single box girder.At present,the research literature on aerodynamic interference of twin box bluff girders with variable cross section is relatively few,and the parameters such as height-width ratio,spacing and wind attack angle of twin box girders do not change much.These results are helpful to understand the aerodynamic interference laws of twin box bluff girders with variable cross section,but they are still far from the general application of practical engineering.In view of this,in this paper,the aerodynamic characteristics of twin box bluff girders with variable cross section with different height-width ratios are further studied under different spacing and wind attack angle.The main work of this paper is as follows:(1)A wind tunnel test device for aerodynamic characteristics of twin box bluff girders with variable cross section was designed,which is easy to adjust the wind attack angle and spacing ratio(D/B,D is the net spacing of double box girders and B is the width of cross-section).The three-component force coefficients and wind pressure coefficients of four kinds of twin box bluff girders with different height-width ratios were measured by this device,and compared with the corresponding values of single box girder.The range of wind attack angle is-10° to 10°,and the range of spacing ratio is 0.025 to 3.0.(2)The interference effect of the drag coefficient of the upstream box girder is not obvious,and it is mainly reflected in the distance range of D/B?1.The interference effect of the drag coefficient of the downstream box girder shows a significant reduction effect.The smaller the distance is,the larger the height-width ratio is,the more obvious reduction effect is.The interference effect of the lift coefficient of the upstream box girder is mainly the reduction effect under the combination of small spacing and large wind attack angle,while the interference effect of the downstream box girder is the significant reduction effect.When height-width ratios are 0.3 and 0.4,the disturbance effect of upstream box girder's torque coefficient can be neglected.When height-width ratios are 0.6 and 0.8,the disturbance effect of upstream box girder's torque coefficient mainly shows the amplification effect in the range of D/B?1.The lower the distance is,the more obvious the reduction effect is.(3)The interference effect of wind pressure coefficient of double upstream box girder is not obvious.The interference effect of wind pressure coefficient of downstream box girder is significant.Compared with other regions,the wind pressure coefficient interference factors of the undersurface of windward flange(area ab),the front end of windward flange(area bc)and the bottom surface(area gh)of the windward side flange of the downstream box girder are all less than 1,showing a significant reduction effect.