Study On VIV Response And VIV Suppression Measures Of Downward Wind Fairings Of Cable-stayed Railway Bridge With Rectangular Steel Box Girders

With the increase of the span of railway bridges in China,the structure of railway bridges is more gentle and easy to vibrate under the action of wind.Because of its strong integral stiffness,the rectangular steel box girder has been gradually applied to long-span railway cable-stayed bridges.But it makes the main girder more susceptible to vortex-induced vibration(VIV)because of the characteristics of the blunt body section.VIV is a kind of amplitude limiting vibration caused by vortex shedding.It will not cause catastrophic consequences such as bridge collapse,but has a great influence on automobile ride comfort and fatigue damage.Therefore,it is necessary to study the VIV and vibration suppression measures of railway cable-stayed bridges with rectangular girder.In this thesis,a bridge across the Yangtze River with a main span of 672 m is taken as the engineering background.In view of its main girder with rectangular section,wind tunnel test and numerical simulation methods are used to discuss the VIV performance of the main girder,and the VIV suppression effects of different aerodynamic measures are compared to explain the mechanism of the occurrence of VIV and the VIV suppression mechanism of aerodynamic measures.The work carried out and the conclusions obtained are as follows:(1)The VIV performance of the rectangular girder section was studied through the 1:50section model wind tunnel test,and the VIV suppression performance of the separated closed outer pavement railing,inverted-L apron,baffle and wind fairing was studied and compared.It was found that the downward wind fairing had good capability of VIV suppression.(2)Through the 1:50 section model wind tunnel test,the influence of the shape of the wind fairing on the VIV suppression performance of the rectangular main beam was further studied.The VIV suppression ability of downward wind fairing is better than that of symmetrical and upward wind fairing;The smaller the angle of the triangular wind fairing,the stronger the VIV suppression ability;The traditional triangle wind fairing can’t reduce the amplitude of VIV significantly,so a platform needed to add to the top of it,and make it become a quadrilateral wind fairing with platform,which can effectively suppress the VIV.For quadrilateral wind fairing,the smaller the angle of the wind fairing,the longer the length of the platform,the stronger the ability of VIV suppression.The length of the platform for the influence of the ability of VIV suppression is greater than the influence of the angle of the wind fairing(For the influence on the ability of VIV suppression,the influence of the length of the platform is greater than the influence of the angle of the wind fairing).(3)Through the wind tunnel test of 1:25 large scale section model and the aeroelastic wind tunnel test of full bridge model,the VIV suppression performance of the quadrilateral wind fairing with platform is verified,and the optimal aerodynamic selection of the wind fairing is finally determined.(4)The CFD software was used to simulate the 2D unsteady flow of the original rectangular section and the section installed the wind fairing.Then,the flow characteristics around the original rectangular section and the evolution process of vortex shedding are analyzed,and the differences of the flow around the section and the vortex shedding characteristics before and after setting the wind fairing are compared.Finally,the mechanism of VIV generation and the vibration suppression mechanism of the wind fairing are explained by the characteristics of the surface pressure distribution and the characteristics of periodic aerodynamic forces.