The Effects Of Turbulent Wind On Flutter Characteristics And Motion-induced Aerodynamic Force Of The Streamlined Box Girder

Along with increase of span,flutter stability has become one of the key factors in design of long-span bridges.The present experimental study on flutter stability of long-span bridges are mainly carried out in the uniform flow,which is quite different from the atmospheric boundary layer wind field at the bridge site.Therefore,the study on flutter stability of bridge in turbulent flow possesses a profound significance.Two kinds of grid turbulent wind fields and three kinds of boundary turbulent wind fields were generated in the wind tunnel.Then the effects of turbulence on flutter characteristics of the streamlined box girder were studied through a series of sectional model tests and taut strip model tests.Subsequently,influences of turbulence on flutter derivatives of the streamlined box girder were investigated by the forced-vibration method.Based on the identified flutter derivatives,the flutter stability of the sectional model and taut strip model was analyzed using two-dimensional flutter analysis method and three-dimensional method respectively.Afterwards,a practical evaluation method for the critical flutter velocity of streamlined box girder in turbulent flow was proposed according to the flutter analysis results.In order to study the effect of turbulence on flutter characteristics and motion-induced aerodynamic force of the streamlined box girder,the works summarized in follows are conducted:1.The research progress of wind induced vibration of long-span bridges is reviewed and the current research on the effect of turbulent flow on flutter stability of long span bridges is summarized.The bridge flutter analysis theories and the flutter derivatives identification methods are introduced.2.Two kinds of grid turbulent wind fields and three kinds of boundary turbulent wind fields were generated in the wind tunnel by using the grids and the atmospheric boundary layer simulator.Through sectional model and taut strip model wind tunnel tests in uniform and turbulent flow fields,the influence of turbulence on flutter characteristics is studied.The result shows turbulence has significant impact on the flutter characteristics of streamlined box girder.3.By using a newly developed two degrees-of-freedom forced vibration device with high measuring accuracy and simple operation,the flutter derivatives of a thin flat plate sectional model are identified through forced vibration method.The identification results verify the reliability and accuracy of the forced vibration device and the identification method.The flutter derivatives of the streamlined box girder in different flow fields are identified by forced vibration method and the experimental results show that turbulent flow has no impact on the trends of flutter derivatives of the streamlined box girder while has influence on the value of the derivatives.And turbulent flow increases the discreteness of flutter derivatives.4.A two-dimensional flutter analysis program is compiled and verified.Based on the identified flutter derivatives,the critical flutter velocities of sectional model under different conditions are calculated respectively.The analysis results indicate that the calculated critical flutter velocities of the sectional model show good accordance with the critical divergence wind velocities of wind tunnel tests in turbulence.5.A three-dimensional flutter analysis program are compiled and verified.Considering the effects of the spanwise correlation of the self-excited aerodynamic force in turbulence,the critical flutter velocities of the taut strip model under different conditions are calculated respectively.The analysis results show that the calculated critical flutter velocities of the taut strip model are in good accordance with the critical divergence wind velocities of wind tunnel tests in turbulence.6.According to the comparison of the analytical results of critical flutter velocities and wind tunnel test results in turbulent flow field,a calculation method for the critical flutter velocity of long-span bridges in consideration of spanwise correlation of the self-excited aerodynamic force in turbulent flow field is proposed.