Experimental Study On Wake-induced Vibrations Of Four-cable Hanger Of Suspension Bridge And Its Reynolds Number Effects

Suspension bridge multi-cable hanger are prone to wake-induced vibration due to strong aerodynamic interference between the cables.The field test results of the hangers of Xihoumen Bridge show that the vibration amplitude of leeward cable is significantly larger than that of windward cable,and its trajectory is close to ellipse,which is consistent with the main characteristics of wake induced vibration.The researchers conducted corresponding force measurement,vibration measurement wind tunnel tests and theoretical analysis to study the mechanism of aerodynamic interference between the cables of suspension bridge hanger.However,existing studies have mainly focused on double-cable hanger,which are different from the four-cable hanger of Xihoumen Bridge;in addition,the test wind speed is single and constant.To this end,this article uses the No.2 hanger of Xihoumen Bridge as the engineering background to study the wake-induced vibration characteristics and Reynolds number effect of four-cable hanger.The main contents and results are as follows:(1)Using the balance force wind tunnel test method,the effect of Reynolds number on the aerodynamic force of the wake cable of a smooth double-cable hanger was studied.Three typical wind speeds were selected in the test,and the variation of the aerodynamic force of the wake cable with the relative spacing of the cable at each wind speed was measured.On this basis,several typical positions where the aerodynamic force changes drastically with the relative spacing are selected,and the influence of the Reynolds number on the aerodynamic force of the wake cable is studied in the subcritical Reynolds number region.The results of the study indicate that there are two peaks in the two-dimensional contour plot of the average lift coefficient of the wake cable,which are the "inner lift peak" near the wake centerline and the "outer lift peak" slightly away from the wake centerline.The two peaks are connected somewhere in the range of X=3.5～3.75,the specific position is affected by the Reynolds number.The magnitude of the average lift coefficient is not directly related to the frequency of vortex shedding,but when the average lift coefficient reaches 1.0 or more,the peak value of the lift coefficient power spectrum curve cannot be observed.(2)The wind tunnel test method of balance force measurement was used to study the differences in the aerodynamic characteristics of the wake cable of parallel wire and wire rope four-cable hanger.Ensure that the relative positions of the three upstream cable are fixed,adjust the position of the wake cable,and measure their aerodynamic characteristics at different spatial positions.Change the different wind angle of attack,repeat the above test,and study the aerodynamic performance of wake cable with wind angle of attack.The resultsshow that the average aerodynamic coefficient of parallel wire hanger is more sensitive to spatial coordinates;the wind angle of attack has a greater influence on the spatial distribution of the average aerodynamic coefficient of four-cable hanger,especially the smooth surface parallel wire hanger.(3)The wake induced vibration response characteristics of parallel wire and wire rope four-cable hanger were measured by aeroelastic model test in wind tunnel.The effect of Reynolds number and wind angle of attack on the wake cable’s vibration characteristics was studied,the motion characteristics of the wake cable’s large vibrations were studied,and the effect of the structural damping ratio on the wake-induced vibration of the four-cable hanger was investigated.The results show that under the structural parameters of Xihoumen No.2hanger,the most unfavorable wind angle of attack for wake-induced vibration of the two types of four-cable hanger is around 70°,but the range of the angle of attack of the parallel wire hanger is wider.At a wind attack angle of 70°,the stable vibration trajectories of wake-induced vibration of both types of hanger are clockwise elliptical,but the aerodynamic negative stiffness effect of parallel wire hanger when wake-induced vibration is more obvious.When the structural damping ratio is increased to 0.67%,the wake-induced vibration of the wire rope hanger is well controlled.