Experimental Research On The Effect Of Stay Cables Configuration On Aerodynamic Stability

With the increasing of span of cable-stayed bridges,stay cables are becoming longer and longer.Therefore,for the sake of characteristics of large slenderness ratio,small stiffness and low damping,stay cables emerge wind-induced vibration easily,such as vortex-induced vibration,wake galloping,rain-wind induced vibration and dry galloping.Rain-wind induced vibration and dry galloping are of great amplitude and serious harm among them.In addition,the surface damages and cross-section shape changes(defect)of stay cables may occur under the external action of wind,sunshine,scratch and collision during service.For the surface state has a significant influence on the aerodynamic force and flow pattern of stay cables,it is important to study the aerodynamic stability of stay cables with surface damages and cross-section shape changes(defect)for improving the service life of stay cables.Also,it is of great meaning to explore new cables which can reduce vibration.In this paper,the damages of stay cables were simulated by the notches and sections along the length of the models,and the cross-section shape changes(defect)of stay cables were simulated by the micro-elliptic cross-section models.The wind-induced vibration characteristics of stay cables on two conditions were analyzed,compared with the results of standard cylindrical stay cables.At the same time,the wind-induced vibration characteristics of wave-shaped stay cables with specific parameters were studied.The results showed that:(1)The wind-induced amplitude and vibration center of the surface-damaged cables are similar to those of the standard cylindrical cable.However,it is noteworthy that the critical region advances obviously,when wind angle of attack is 60°,wind-induced vibration occuring at lower Reynolds number.And the time-frequency characteristics of vibration are similar to those of the standard cylinder.From the analyses of mechanisms,the wind-induced vibration is related to flow field during critical Reynolds number possibility.Also,It may be vortex-induced vibration at high wind speed.(2)The maximum amplitude of micro-elliptical cross-section cables in the ranges of wind angles of attack are quite different,some very small,almost no vibration,some very large,even reaching 2.25 times of that of the standard cylindrical cable.Its time-frequency characteristics are different from surface damage and standard cylindrical cables,with vibration being more stable.The time-history curves are close to the standard sinusoidal curve,and the predominant frequency is more prominent.It is closer to galloping,and can be predicted by Den Hartog galloping mechanism.(3)It's significant for the aerodynamic stability of the wavy cables,for there is almost no obvious wind-induced vibration in the range of Reynolds number.And the aerodynamic drag increased hardly.These indicate that the wavy cables are of good performances of reducing vibration and drag.In addition,its lift remains almost zero in the range of Reynolds number,which may be the reason why it does not have large wind-induced vibration.