Experimental Research Of The Mechanism Of Rain-wind Induced Vibration Of Stay Cable Model

In the construction of long-span bridges,cable-stayed bridges are more and more used in engineering construction because of their beautiful shape and high spanning capacity.Because of the soft structural system of long-span cable-stayed bridges,the cable-stayed cables subjected to the combined action of wind and rain may have a large cross-wind vibration under the weather of rain.This large vibration of stay cables caused by the combined action of wind and rain is called rain-wind induced vibration(RWIV).The phenomenon of RWIV of stay cables seriously affects the fatigue life of the end Anchorage device,and then affects the durability and safety of the bridge,as well as the comfort of drivers in the process of driving.It has been 40 years since the phenomenon of RWIV of stay cables was discovered,however,a widely accepted explanation of the mechanism of RWIV has not been put forward.In this paper,based on the wind tunnel laboratory,the characteristics of RWIV of cable model,the dynamic characteristics of the upper rivulet and the characteristics of wake flow are analyzed and studied.The main research work is as follows:The RWIVs of the cable model is reproduced in the wind tunnel test by the method of artificially induced upper rivulet.Through the accelerometer,the vibration characteristics of the cable model are obtained when the RWIVs occurs.The coordinate system is depicted in advance on the surface of the model,and the motion information of the upper rivulet is obtained by monitoring and identifying the upper rivulet in the RWIVs by a high-speed camera.Through the analysis of model vibration and upper rivulet oscillation,the phenomenon of low frequency resonance between upper rivulet and stay cable is observed.The high frequency particle image velocimetry(PIV)is used to visualize the wake flow field when RWIVs occurs,and the wake flow information with time resolution is obtained for the first time.Through the POD analysis,the mode distribution of the wake flow during RWIVs is obtained.It is found that the backward shift of the second mode occurs with the decrease of vibration.Through the fast Fourier transform of the wake flow field in the whole basin,it is found that the frequency of vortex shedding in the wake flow is the same as the natural frequency of the structure.The results show that the RWIVs of stay cables is an air-water-structure coupling co-frequency resonance phenomenon,and its mechanism is discussed.