Experimental Study On Effect Of Surface State On Aerodynamic Force And Wind-induced Vibration Of Stay Cables

The number and length of stay cables increase with developing span of cable stayed bridge.The wind loads on stay cables have being dominated in the cable-stayed bridges.For example,the contribution of wind loads on stay cables exceeds half of the wind loads on the whole bridge.During its service,the variation of the surface condition leads to significantly influence the aerodynamic forces on stay cables.So it is necessary to accurately calculate the wind loads on stay cables.Since its high flexibility and low damping,the stay cables are prone to vibrate under wind loads.The wind-induced vibrations of stay cables,especially rain-wind induced vibration and dry galloping,have widely concerned by researchers.In this paper,the wind tunnel experiments are used to illustrate the effect of surface conditions on aerodynamic forces and wind-induced vibrations at various cases.It mainly includes four parts.1.The effects of end condition of the model of stay cables on aerodynamic forces were studied.By fitting the compensation model and end plates at both ends,the effects of the compensation model and the size of the end plate on the aerodynamic forces and wind pressure distribution on the model were revealed.The results show thatthe compensation model cannot effectively eliminate the effects of the end effect when the slenderness ratio is small.For using end plates,when the diameter of the end plate is larger than 4 times of the diameter of the model,the influence of the end effect is ignorable.When end plates are installed on the model,the load on the end plates should be considered.2.Study on aerodynamic and wind-induced vibration characteristics of stay cables with smooth surface.A notable lift coefficient about 1.3 is observed in the critical Reynolds number range,which is larger than drag coefficient at same Reynolds number.The aerodynamic forces on stay cable evaluated by wind tunnel tests and Chinese code are compared.In some cases,wind loads in the code are smaller than that from the wind tunnel tests.The aerodynamic force coefficients of stay cables are recommended to the engineering applications.The wet surface conditions cause the occurrence of Reynolds number effects to lower Reynolds number,and the minimum drag coefficient is larger than that in dry conditions.3.Study on aerodynamic and wind-induced vibration characteristics of stay cables with rough surfaces.The results show that with the increase of the roughness,the minimum drag coefficient of the cable increase.Meanwhile,the lift coefficient decreases.The aerodynamic stability of the cable is improved at high Reynolds number for the rough surface model.When the roughness of the model is different,the wet condition has different effects on the stay cables.4.Study on aerodynamic and wind-induced vibration characteristics of stay cables with helical Cables lines.The results show that for same helical line space,when helical line diameter becomes large,the drag coefficients increase with increasing diameter of helical line for the same helical line space.Meanwhile,the lift coefficient diminishes.When the helical line diameters are same,the drag coefficient increase and the lift coefficient diminishes with the decreasing helical line space.With helical line,the aerodynamic stability of the cable is improved at high Reynolds number.The aerodynamic stability of the cable also is improved at high Reynolds number for the wet surface model.