| With the advancement of our country’s railway bridge design and construction technology,steel box girder has gradually been applied to long-span railway cable-stayed bridges due to its good integrity,high rigidity,low wind load,and convenient maintenance.In view of the higher requirements for vertical rigidity of railway traffic,the steel box girder of railway bridges generally adopts a rectangular section,which makes the section susceptible to vortex-induced vibration(VIV).At the same time,the installation of track slabs and other facilities and equipment also increases the bridge deck.The complexity of the vortex may also aggravate the vortex-induced vibration to some extent.In order to systematically study the VIV performance and VIV control measures of the rectangular steel box girder of the railway cable-stayed bridge,this thesis considers the width and height of the main girder when the two-line railway,the four-line railway and the six-line railway are arranged,and adopts the section model wind tunnel test.The method tested the VIV performance of rectangular steel box girder with different aspect ratios,and compared the vibration damping effects of different wind fairings and different horizontal guide.Finally,the three-dimensional VIV amplitude was calculated,and the CFD numerical calculation method was used for preliminary calculation.The flow field mechanism of the vortex vibration damping effect of the wind fairing on the rectangular steel box girder of the two-track railway is explained.The main work content and conclusions are as follows:Rectangular steel box girder models with aspect ratios of 3.88:1,6.4:1,and 8.92:1(with track slabs and other components and facilities)were designed and produced,the scale set as1:90.Using section model wind tunnel tests,the VIV performance of three rectangular steel box beams with different aspect ratios under different wind attack angles is obtained respectively.The research results show that the VIV amplitude will decrease as the aspect ratio of the rectangular steel box girder increases,and the VIV amplitude of the rectangular steel box girder with the smallest aspect ratio will be the largest.the amplitude increases significantly as the wind attack angle increases.3 m and 4 m long downward wind fairings and 3 m and 4 m long horizontal guide was designed to test the VIV damping effects of different aerodynamic measures on rectangular steel box girder with different aspect ratios.Obtained from the test were VIV reduction measures for rectangular steel box girder with different aspect ratios.The results of the study show that compared with the rectangular steel box girder with an aspect ratio of 4,the 4m long downward wind fairing has the best VIV damping effect;for the rectangular steel box girder with an aspect ratio of 6.4,a 3m long downward wind fairings can be used.Meet the requirements of vibration control;for rectangular steel box girder with an aspect ratio of 9,the use of a 3m-long horizontal guide can eliminate VIV.Considering the span-wise correlation of the vortex-induced force and the mode shape of a cable-stayed bridge,the three-dimensional VIV amplitude was calculated,and the influence of the VIV amplitude on the railway traffic was simply calculated.At the same time,the aspect ratio was reproduced by CFD numerical simulation.The rectangular rigid flow field characteristics of 4 clarify the inducing effect of large vortex shedding on the upper and lower surfaces on the vortex vibration.At the same time,it is also found that the vortex size is significantly reduced after the wind fairing is installed on it,and the amplitude of the vortex excitation force is also improved.Achieved the purpose of damping vibration.The research results of the thesis can provide references for the wind-resistant design of the rectangular steel box girder of the railway cable-stayed bridge. |
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