Study On High-mode Vortex Vibration Of Cable And Aerodynamic Control Measures For Long-span Cable-stayed Bridge

The stay-cable of long-span cable-stayed bridge has the characteristics of small stiffness,light weight and low damping ratio.When the cable damper has not been installed in the bridge construction period or the performance of cable damper has degraded or failed in the bridge operation period,although the cable adopts the aerodynamic control measures for rain-wind-induced vibration(RWIV),such as setting pits on the cable surface or winding small-diameter helics,there are still wind-induced vibration on some long-span cable-stayed bridge.For example,in recent years,some long-span cable-stayed bridges,such as Sutong Yangtze River Highway Bridge,Jingyue Yangtze River Bridge and so on,have experienced obvious high-order vibration of stay-cables.The high-order vibration of the stay-cable has the characteristics of small displacement,large acceleration and high frequency.If it can not be effectively controlled,it will cause fatigue problems near the stay-cable anchorage area,which will affect the service life of the stay-cable and bring hidden dangers to the safe operation of the bridge structure.With the further increase of the span of the cable-stayed bridge,the length of the longest stay-cable will increase from about 580 m to 750 ～ 800 m.The high-order vibration of the super long cable has become one of the key technical bottlenecks restricting the development of the long-span cable-stayed bridge.At present,the high-order vibration of long-span cable-stayed bridge has been concerned widely by scholars at home and abroad.Based on the project of Sutong Yangtze River Highway Bridge,combined with the second sub-project of "Research on mechanism and control measures of high-order vibration of super long cables"(entrusted by Jiangsu Sut ong Bridge Co.,Ltd.),this paper studies the phenomenon of high-order vibration of super long stay-cables and aerodynamic control measures by combining field measurement and wind tunnel test.The main contents of this paper are as follows :(1)Based on the Sutong Yangtze River Highway Bridge,the short-term monitoring data of wind-induced vibration response of five cables(NA31U,NA30 U,NA29U,NA18 U and NA09U)of Sutong Bridge are processed and analyzed.The characteristics of acceleration responses time history and variance of acceleration response root with wind speed and wind direction are analyzed.(2)Based on the phenomenon of high-order vibration of NA30 U cable of Sutong Bridge,the cross wind single degree of freedom vortex-induced vibration(VIV)test of horizontal cable segment model is carried out.First of all,the vortex vibration tests of cables with indent surface,smooth surface with small diameter helical wires(d =2mm,3.5mm)are carried out respectively;Then,the vortex vibration tests of cables with different damping ratios are carried out for cables with indent surface and smooth surface respectively;Finally,the wind tunnel tests of aerodynamic control measures for cables with helical wires of different parameters are carried out.(3)Considering the influence of stay-cable inclination angle and wind yaw angle on VIV responses of stay-cable,a special device for two degree of freedom s of inclined stay-cable segment model with elastic suspension is developed,which can adjust stay-cable inclination angle and wind yaw angle conveniently.The experimental study on the VIV response and aerodynamic control measures of the stay-cable with different inclinations and wind yaw angles was carried out by using the developed test device in this paper.Finally,the control effect of the heli cal wires with specific parameters on the stay-cables with different inclinations and wind yaw angles was verified.(4)Considering that the setting of the helix changes the aerodynamic shape of the cable,and changes the aerodynamic force of the cable.In order to deeply study the influence of helix on the aerodynamic force of cable and analyze the mechanism of vibration reduction of helix,the wind tunnel test was carried out.Finally,the test shows that the helix reduces the aerodynamic force of the cable in cross wind direction to a great extent,so as to achieve the effect of vibration reduction.