Study On Vortex-induced Vibration And Aerodynamic Characteristics Of Stay Cables With Helical Lines

The stay cables of cable-stayed bridges have the characteristics of large slenderness ratio,low damping and small stiffness.Therefore,wind-induced vibration,especially rain-wind-induced vibration(RWIV),has always been a long-term research hotspot.RWIV is the strongest one of all known cable vibrations,with the largest amplitude and serious harm.In order to suppress RWIV,winding helical lines on the surface of stay cables is a common aerodynamic measure.Recently,the problem of vortex-induced vibration(VIV)of stay cables has attracted more and more attention.This is a limiting vibration with self-excited properties that occurs under frequent wind speed.Although the amplitude is small,the frequency of occurrence is high,which will increase the stress in the anchorage zone and easily cause fatigue damage to the structure.The change of aerodynamic force of stay cables after winding helical lines and its influence on VIV performance have become the focus of research and design.The main conclusions are as follows:In order to study the influence of helical lines with different parameters on the VIV characteristics and aerodynamic force of stay cables,the section model wind tunnel vibration,pressure and force tests were carried out for a smooth cable as well as them with helical lines.The helical parameters include number,diameter and winding spacing.The mechanism of drag reduction and vibration suppression of helical lines is explained from the aspects of VIV characteristics,aerodynamic characteristics and wind pressure distribution characteristics.The main conclusions are as follows :(1)The VIV amplitude of one helical line wound on the surface of stay cable is much larger than that of two or three helical lines.In the subcritical Reynolds number region.The mean drag coefficient of stay cable with two helical lines is smaller than three helical lines.Increasing the number of helical lines will make the position of the separation point gradually move to the leeward side,the mean wind pressure coefficient and the fluctuating wind pressure coefficient are asymmetric.The spanwise correlation of the base pressure coefficient on the leeward side is significantly reduced,and the spanwise flow state shows three-dimensional flow characteristics.(2)The VIV of the stay cable wound with smaller diameter helical lines with d≤10 mm is obvious.In contrast,large diameter helical lines with d＞10 mm can significantly reduce the amplitude of VIV response of stay cables,and its fluctuating lift coefficient is significantly lower than that of the cable without helical lines,which proves the effectiveness of winding the large diameter helical lines to control the VIV response.With the increase of the helical diameter,the overall mean wind pressure coefficient of the stay cable gradually increases,and the fluctuating wind pressure coefficient gradually decreases.(3)The influence of the winding spacing on the VIV of the stay cable is related to the diameter of the helical lines.When the diameter is small with d ≤10 mm,the influence of the winding spacing on the VIV is not obvious.When the helical diameter is large,with d＞10 mm,spacing directly affects the suppression effect of VIV.