Field Measurement And Wind Tunnel Tests Of Vortex-induced Vibration Of Long-span Cable-stayed Bridges

The construction of long-span bridges has become more and more common in recent years.However,due to the low damping of the cable-stayed bridge,the cables and main girder of the cable-stayed bridge are prone to wind-induced vortex induced vibration(VIV)under the action of wind load.Which affects the normal use of the cable-stayed bridge.In this paper,through the wind tunnel segment model test of a cable-stayed bridge,the VIV performance of the main girder.For the health monitoring of a Yangtze River bridge,the wind field characteristics at the bridge site and the correlation of VIV is studied.FM-CEEMD is applied to identify the modal parameters of the cable through the environmental excit ation and sine excitation vibration data of the cable.The main work of this paper is as follows:,(1)The dynamic characteristics of the full bridge were analyzed.Based on the results of the dynamic characteristics,the segment model experiment of the bridge was designed.The VIV stability of the main girder of the bridge was experimentally studied.Wind tunnel tests were carried out on the VIV stability of a segmental model with different damping ratios and aerodynamic shapes.The results show that increasing the damping ratio can effectively reduce the vertical bending acceleration amplitude and increase the vibration-starting velocity.Move the maintenance vehicle track inward,enclosed sidewalk railings,and add vertical skirt board can effectively reduce the vertical VIV of the cross section.Measures such as move the maintenance vehicle track inward,enclosed sidewalk railings,and 45 ° inclined webs can effectively reduce the torsional VIV of the section.(2)The dynamic equation of the stay cable is deduced,and the frequency of the stay cable is calculated.The improved empirical modal decomposi tion method(FMCEEMD)was applied to the modal identification of the vibration data of the stay cable with sinusoidal excitation and environmental excitation,and the modal damping ratio was obtained.The results show that the damping ratio of the second and third modes of the cable has increased from 0.87% and 0.53% to 1.4% and 1.2% after the installation of the damper.Low-order mode damping ratio of the stay cable increased significantly and the modal damping ratio of the cable has a greater correlation with the amplitude.(3)Based on the cable monitoring data,the VIV characteristics of the cable are studied.The VIV of the cable only occurs within a range of wind speed.The large-scale VIV of the cable only occur when the turbulence is small and at a specific wind direction angle range.In-plane acceleration and out-of-plane acceleration of the cable are effectively controlled after the damper is installed.The cable vibration is highorder multi-mode VIV.With the development of VIV,the small amplitude vibration near the dominant frequency is reduced,and finally only the dominant frequency is left,the cable generates VIV at this frequency.