| The span of cable-stayed bridges continues to increase,and stay cables become longer and longer.Thus,wind loads on stay cables become more significant.Taking Su-Tong Yangtz River Highway Bridge as an example,wind loads on the stay cables contribute 60% of wind loads on the whole bridge to the displacement and internal force of the main girder.Moreover,stay cables exhibit large aspect ratio,small stiffness and low damping.Therefore,stay cables are prone to various wind-induced vibrations,including rain-wind-induced vibration,vortex-induced vibration and dry galloping.Frequent wind-induced vibrations will affect the safety and applicability of stay cables and even cable-stayed bridges.Aerodynamic countermeasure is one of the measures to control the wind-induced vibrations of stay cables,which includes many types.Different countermeasures exhibit different control effects and impacts on aerodynamic forces.It is of great theoretical value and engineering application prospect to investigate and develop new aerodynamic countermeasures,which can not only control wind-induced vibrations but also reduce wind loads.By means of wind tunnel tests,the effects of O-rings and wavy shape on the aerodynamic force,wind pressure distribution,vortex-induced vibration and dry galloping are specially studied.The influence pattern of the two countermeasures on the aerodynamic characteristics from the subcritical regime to the critical regime is determined.The influence pattern of the two countermeasures on the vortex-induced vibration and dry galloping is obtained.The geometrical parameters that can reduce drag or control vibration are summarized.In addition,the mechanisms of reducing drag and controlling vibration are discussed.The current work can provide theoretical reference for engineering practice.The main research contents and conclusions are as follows:(1)The aerodynamic force and wind pressure distribution of stay cables attached by O-rings(hereinafter referred to as “ring-attached stay cable”)from the subcritical to the critical regime are investigated.The effect of the parameters(thickness,width,spacing)on the aerodynamic force and the control mechanism are analyzed.Results show that ring-attached stay cables can reduce drag in the subcritical regime,with the maximum reduction of 29.5%.The reason is that the ring can increase the mean basic pressure coefficient in the wake region,and lead to the spanwise pressure gradient,intensifying the three-dimensional flow.However,ring-attached stay cables possibly increase drag in the critical regime,with the maximum increase of 36.4%.The reason is that,as “interference”,the ring will weaken the Reynolds number effect.(2)The influence pattern of the parameters on vortex-induced vibration and dry galloping is investigated.The mechanism of controlling vibration is discussed.Results show that during the tested range of the parameters,the vortex-induced vibration of the ring-attached stay cable is weaker than that of the stay cable without aerodynamic countermeasure(hereinafter referred to as “standard stay cable”).The amplitude can be significantly reduced.When the ring is thicker,wider or closer,the control effect is better.The smaller fluctuating lift and wind pressure in the subcritical regime are responsible for the weaker vortex-induced vibration.Additionally,suitable parameters can effectively inhibit dry galloping.The amplitude can be decreased by up to 35%.When the ring is thinner,wider or closer,the control effect is better.The smaller fluctuating lift in the critical regime and the weaker transition-induced instability are responsible for the controlling of dry galloping.(3)The aerodynamic force and wind pressure distribution of the stay cable with wavy shape(hereinafter referred to as “wavy stay cable”)from the subcritical to the critical regime are studied.The variation pattern of aerodynamic parameters along the spanwise direction is mainly analyzed in the subcritical regime.Results show that the mean drag of wavy stay cables are lower than those of standard stay cables in the subcritical regime.The drag can be reduced by up to 18%.In the subcritical regime,the aerodynamic parameters vary significantly along the spanwise direction for wavy stay cables,reflecting the three-dimensional flow characteristics.In addition,when the waviness degree is higher,the spanwise change is the more drastic.(4)The control effects of wavy stay cables on the vortex-induced vibration and dry galloping responses are studied.The mechanisms of wavy shape controlling these two vibrations are discussed.Results show that,during the tested range of the parameters,wavy stay cables can weaken the vortex-induced vibration.SW3 and LW1 stay cables(λ/D=6.00,a/D=0.09,which are sine and broken line wave,respectively;here,a is the wave amplitude,λ is the wavelength,D is the mean diameter)exhibit better control effectiveness of vortex-induced vibration.However,SW1(λ/D=2.27,a/D=0.09)and SW2(λ/D=6.00,a/D=0.03)exhibit better control effectiveness of dry galloping. |
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