Study On Control And Mechanism Of Flutter Stability Of Streamlined Box Girder For Long Span Suspension Bridges

Flutter stability is frequently one of the controlling factors in long-span suspension bridges design.How to effectively improve the flutter stability of long-span suspension bridges is the key point of wind resistant design.The three main factors affecting the flutter performance of bridge structures,which are bridge structure system,stiffening girder aerodynamic shape and aerodynamic measure.The paper is supported by the National Natural Science Foundation of China?No.51778225?.In this paper,with engineering background of the proposed design of1600m span LingDing suspension bridge,the method of wind tunnel test and numerical simulation is used to study the control measures and mechanism of the flutter stability of the streamlined box girder section.The main research works are as follows:?1?Using wind tunnel test method,the flutter control effects on the streamlined box girder section of the main cable space form of the suspension bridge,the main girder aerodynamic shape and the central stabilizer height were studied.The study shows that the main cable layout has an effect on the critical wind speed of the bridge flutter,which mainly results in the change of the torsional frequency of the bridge structure,thus affecting the critical wind speed of the bridge structure,and the appropriate increase of the width height ratio of the main beam section can effectively improve the critical wind speed of the bridge structure,and set an appropriate height central stabilizer can effectively improve the flutter critical wind speed of streamlined box girder section with horizontal separation board.?2?N-S equations were solved with large-eddy simulation?LES?.Combined with dynamic mesh technology,the Newmark-beta algorithm was embedded in Fluent through user defined function?UDF?,and fluid-structure interaction?FSI?method was established to simulate flutter of bridge decks.The direct flutter critical wind speed of a thin plate was successfully simulated by FSI method,and the correctness of the method was verified.The numerical simulations of the main deck of the 1660-m span suspension bridge were carried out.Comparing the numerical simulation results with the section model test results,the maximum calculation error at the state of the bridge is less than 7%,the maximum calculation error of the case with central stabilizer is less than 15.7%.The calculated value is in good agreement with the test value.The numerical calculation method is not only applicable to the flutter analysis of streamlined box girder with complex auxiliary facilities such as railings and horizontal separation plates,but also can accurately reflect the flutter control effect of the aerodynamic measures of the central stable plate of the bridge section.?3?The flutter control mechanism of the central stabilizer for long-span suspension bridges is analyzed from the height of the central stabilizer,additional wind attack angle and the structure of the flow field.The results show that the aerodynamic derivative A₂^*curve gradually moves downward with the increase of the height of the central stable plate,which will help to improve the flutter performance of the section,and the offset of the A₂^*curve relative to the original section is related to the angle of attack.The existence of the central stabilization plate of the deck makes the additional angle of attack smaller.In the flutter analysis of long-span suspension bridges,it is necessary to consider the influence of additional wind attack angle.The vortex mainly produced by the central stabilizer produces the vertical aerodynamic force on the main cross section of the convective line,which leads to the increase of the vertical movement of the main beam section,and restraining the torsional motion of the main beam section,thus improving the flutter stability of the streamlined box girder section.