Field Measurement And Experimental Study On High-mode Vibration Of Super-long Stay Cables

With the increasing demand for transportation construction in China,the increasing scale of transportation infrastructure will promote the main spa n of the cable-stayed bridge to reach 1200～1500m,and the longest stay cable length will increase from 580 m to 750～800m.The vibration problem of the stay cables will become a critical factor restricting the safety of long-span cable-stayed bridges.In recent years,the significant high-mode vibration of stay cables has been observed in some large-span cable-stayed bridges.If the vibration of the stay cables is not effectively controlled,it may result in the fatigue problems at the anchor ends of the stay cables,which will affect the service life of the stay cables and threaten the safety of the bridges.Moveover,it will also cause the visual insecurity of the peoples on the bridges and cause social concern.Taking the Sutong Yangtze River Highway Bridge(STB)as the engineering background,the characteristics,mechanism and aerodynamic control measures of the high-mode vibration of the stay cables of a super-long-span cable-stayed bridge via field measurements and wind tunnel tests.The specific research content in this study is given as follows:(1)Based on the wind-induced vibration health monitoring system of STB,the in-plane and out-of-plane acceleration responses of the eight cables of STB are monitored on site for two years.During the monitoring period,the relationship between the wind speed and direction at the main girder level at the bridge site with the RMS of acceleration response of stay cables are studied.(2)On the basis of long-term monitoring,the wind environment and the acceleration responses of the stay cables under the action of a typhoon and a downburst are analyzed,respectively.Furthermore,the time history and frequency of the cable acceleration responses of the stay cables,and the correlation between the RMS of the acceleration reponses and the wind speed and direction are investigated,as well as the wind speed and direction of the typhoon.Finally,the wind characteristics of the downburst and the wind-induced responses of the stay cable cables under downburst are analyzied,including the non-stationary wind speed,wind direction,turbulence,fluctuating wind power spectrum of the downburst,and the relationship between the time-frequency characteristics and the RMS of the acceleration responses of the stay cables.(3)Taking the NJ32 D stay cable of STB as a reference prototype,the mode order amplification factor(MOAF)of the stay cable is introduced to desi gn and fabricate the flexible stay cable model for the prototype stay cable based on the similarity criteria for aero-elastic model design.The combination of steel wire rope and copp er tube is used to simulate the aerodynamic shape,weight and stiffness o f the stay cable,and finally the full stay cable aeroelastic model is made.The wind tunnel tests of the high-mode vortex-induced-vibration(VIV)of the flexible stay cable mode l are carried out in a uniform flow field.The acceleration sensor and the vid eo displacement test system are applied to monitor the wind-induced vibration responses of the flexible stay cable model.Firstly,the wind tunnel tests of the flexible stay cbale model with smooth surface under different wind yaw angles are carried out.And the characteristics of acceleration and displacement time histories,frequency and,the mode shapes of the flexible stay cable model under different wind yaw angles are analyzed.Then,the vibration responses of the flexible stay cable s model with double helical fillets of diameter of 0.07～0.10D(D is the dimater of the flexible stay cable model)are studied to verify the suppression effects of the double helical fillets on the high-mode VIV of the stay cables.(4)The force test is carried out on the ri gid segment model of the stay cable with smooth surface and the double helical fillets of 0.07～0.10 D.Firstly,the original average drag and lift coefficients of the stay cable section with smooth surface are analyzed.Then the drag coefficient,lift coefficient of the stay cable with double helical fillets.Finally,the experimental results of the stay cable section with/withou t helical fillets are compared with the experimental results of the dimpled stay cbale with/without helical fillets,respectively.