Aerodynamic Interference Effects Of Twin Separate Box Girders On Aerodynamic Coefficients

In recent years,with the increasing traffic volume,because of the spacious visual effect and good driving condition,bridges with twin separate box girders are increasingly used in the design.Because of the small spacing,there exists aerodynamic interference between twin separate box girders under incoming wind.Aerodynamic coefficients of twin separate box girders are different,compared with those of single box girder.Although aerodynamic coefficients of the recommended value of single box girder is given at?Wind-resistent Design Specification for Highway Bridges?,there is no description of twin separate box girders.For this reason,this paper firstly summarizes the research status of aerodynamic interference of aerodynamic coefficients of twin separate box girders,then study the influence of aerodynamic interference for twin separate box girders with two different section shapes(twin flat box girder and twin bluff body box girder)using wind tunnel test.The main work of this paper includes the following aspects:(1)In the range of-10°~10°,aerodynamic coefficients of twin separate box girders in 15 different spacing(The ratio of net spacing of twin box girder D with width of single box girder B is from 0.025 to 6)were measured through sectional model tunnel test,and compared with those of single box girder.The contour of interference factor of aerodynamic coefficients with the change of wind attacking angle and spacing is given for the first time.(2)The effect of aerodynamic interference for twin flat box girders is as follows: Aerodynamic interference has little effect on the forward box girder and three component coefficients change little;Aerodynamic interference has obvious effect on the leeward box girder.The drag coefficient is reduced,the smaller the distance,the more obvious effect at D/B?1.The influence of lift coefficient is reduced in the negative attacking angle.The smaller distance,the more obvious effect.The influence of torque coefficient is mainly reflected in the large attacking angle.At the positive and large attacking angle,the amplification effect is observed.At the negative and large attacking angle,the reduced effect is observed.(3)The effect of aerodynamic interference for twin bluff body box girder is as follows: The aerodynamic interference effect on the aerodynamic coefficients of forward box girder can be ignored when D/B?2.Aerodynamic interference effect on the aerodynamic coefficients of the leeward box girder is obvious.The influence on drag coefficient and lift coefficient are reduced,the influence on torque coefficient is concerned with both wind attacking angle and spacing.