Vortex-induced Vibration And Counter-measures Of Cable-stayed Bridge With Composite Girder

With the increasing span of bridges,the development of the bridge towards the light and soft direction makes the wind resistance problem of large-span bridges more and more prominent.The composite girder is a kind of main girder widely used in the cable-stayed bridges design.A large number of studies demonstrated that the characteristics of the bluff body section can easily cause the vortex-induced vibration(VIV)of the main girder.VIV is caused by periodic vortex shedding around the bluff body with a limited-amplitude vibration,which will not only cause direct damage to the bridge,but induce comfort problems and fatigue damage for using performance of the bridge.Therefore,it is of great significance to research the response of VIV and control measures for cable-stayed bridges on the composite girder.Due to the complexity of fluid-structure coupling,there is no mature theory obtaining analytical solutions to VIV response.Wind tunnel tests are now commonly used to study the VIV of bridges.The full aeroelastic bridge model wind tunnel test has a long test cycle and high cost,it is easily affected by the Reynolds number effect.Thus sectional model wind tunnel tests are commonly used to study the VIV of structures in the actual project.Taking a long-span cable-stayed bridge with a main span of 486 meters as an the engineering background,the locked wind speed and VIV response of the edge girder section were studied via a series of section model wind tunnel tests.By improving the aerodynamic shape of the main girder section,the effects of the vortex-induced vibration of the main beam on the sidewalks of the external walkways,horizontal flow dividers,the central stabilizing panels,the skirt panels,the lower deflectors of the longitudinal beams,and the wind nozzles were studied.Using the existing theory,the VIV responses of the sectional model tests were converted to the actual VIV response of the full bridge.Finally,the bridge was used as an example to compare the different specifications regarding VIV responses.The research indicates that: The bluff body characteristics of the side girder section make it easy to induce VIV at a low wind speed,which should be emphasized in the design of the bridge.The VIV of the edge girder composite girder can be controlled with the vertical aprons on the each side of the composite girder,because a recirculation zone can be formed between the vertical apron and the main longitudinal girder to reduce the vortex formed when the air flow is separated.Whether the vortex induced cross-directional correlation has significant influence on the VIV response of real bridges.Taking the bridge as an example,the allowable value for the vertical VIV of bridge design specifications are relatively close,but the allowable amplitudes of the torsional VIV are quite different.