Investigation Of Vortex-induced Vibration Of Triple-box Steel Girder

One belt,one road and other important national strategies,and so far,have built many kilometre suspension bridges and cable-stayed bridges.It is foreseeable that in the future China will build more long-span bridges.However,as the span of bridges increases,the stiffness of bridge structures is getting smaller,and is vulnerable to the problem of flutter.In order to ensure the flutter stability and static wind stability of the bridge and increase the traffic carrying capacity of the bridge structure,Italy’s Messina bridge first proposed the design scheme of tiple-box girder.The new Xihoumen highway and railway bridge and Taoyaomen highway and railway bridge in China are constructing with the triple-box girder cross-section.Although the triple-box girder has a great flutter stability due to the two gaps between three girders.The flow field around gaps will be significantly complex and may cause vortex-induced vibration phenomenon.In this paper,the vortex-induced vibration of triple-box girder was studied based on wind tunnel test and CFD numerical simulation.The main research works and achievements are as follows:(1)In this part,the aerodynamic coefficient of large chamfer triple-box girder was tested based on wind tunnel test and CFD numerical simulation,and verified with each other.Then analyzing the flow characteristics of triple-box girder at three different wind attack angel(-3,0 and +3).The wind tunnel test results show that,with wind attack angel increasing,the aerodynamic drag coefficient shows a downward and upward trend with a lowest value nearby 7°;lift coefficient shows an increase trend and moment coefficient shows a decrease trend.In numerical simulation,it is show that there is a good reliability at-3°～+3° but not at large attack angel which may caused by aerodynamic interference and complex flow field generated by gaps between three girders.(2)The wind tunnel section vibration tests under 1:60 reduced scale were carried out on three different types of inner web,i.e.circular section,large chamfered section and small chamfered section.Vertical vibration was observed on all three types of model,and rotational vibration was only observed on circular section.(3)The 1:60 and 1:30 reduced scale wind tunnel test of the small-chamfered threepiece box girder section were carried out.The results show that,with the increase of the Reynolds number,the vortex vibration interval of the triple-box girder is delayed and the maximum amplitude of the vortex vibration increases,showing a Reynolds number effect different from that of the flat steel box girder.(4)Simulation of vortex-induced vibration of triple-box girder was developed based on CFD through dynamic grid technique and SST turbulence model.The reliability of CFD numerical simulation for vortex-induced vibration of triple-box girder is verified by the results of wind tunnel test.Meanwhile,the flow field characteristics in static state are compared with those in steady state.It is demonstrated that nonlinear components existing in aerodynamic lift force.The vortex-induced vibration of a triple-box girder is caused by periodic vortex shedding at the trailing edge of the top and bottom plates of the upstream box girder,which is captured by the bottom plates of the middle box girder when the structure moves downward,resulting in reattachment phenomenon and periodic vortex induced force.Under the static state of the wind speed corresponding to the maximum amplitude,bubble separation and reattachment occur at the leading edge of the top plate of the middle box girder,while the vortex reattachment phenomenon of the upstream box girder does not appear at the bottom plate.