Study On Calculation Method For Vortex-Induced Vibration Of Variable Cross-Section Long Span Continuous Steel Box Girder Bridge

Starting from the classic semi-empirical linear vortex induced vibration model and Scanlan’s nonlinear vortex induced vibration model, with the application of the variation coefficient parameter, which describes the two-dimensional sectional different aerodynamic of variable cross section, and the vortex aerodynamic span wise correlation function, the main object of this thesis is to investigate the assessment method and the theory for vortex induced vibration of long span variable cross section continuous beam bridge. The vortex aerodynamic equation is extended from two-dimensional cross section to three-dimensional variable cross section bridge.An overview of the investigation on the bridge wind engineering is briefly provided. Considering the vortex induced vibration in several continuous beam bridges, the significance of sucn research is indicated. In order to study the mechanism of vortex induced vibration and the vortex induced vibration theory model, the main research methods of vortex induced vibration and the present achievements has been summarized. Also, according to principles of fluid mechanics and employing smoke trails method, flow characteristics are observed and described by the vortex induced vibration of the typical variable cross section rectangular beam. For standard prism and variable cross section prism, the correlation of vortex induced force in variable cross section beam under vortex induced vibration is comparative investigated.Based on the classic semi-empirical linear vortex induced vibration model and Scanlan’s nonlinear vortex induced vibration model, three-dimensional semi-empirical linear vortex induced vibration model and nonlinear vortex induced vibration model are derived, which is applicable to the variable cross section continuous beam bridge. For the amplitude of vortex induced vibration, what is the most concern in Engineering, three-dimensional semi-empirical vortex induced vibration model for variable cross section beam bridge is discussed, so that the stable solution of the steady-state vibration is obtained. And the simplified calculation method of vortex induced vibration of variable cross section beam bridge is proposed, the vortex induced vibration of variable cross section beam bridge is obtained from the amending coefficient, what is commonly used in engineering calculation.Employing the concept of variation coefficient, the results of the uniform section model test are amended for variable cross section model.For the vortex induced vibration of the special variable cross-section square beam, the semi-emprical linear model and nonliear model are theorized, and the result is calculated and confirmed by wind tunnel experiment. In order to facilitate its engineering application, parameters in the vortex induced force modal are further simplified. Aerodynamic parameters that changes with cross section is simplified to linear variation; and the attenuation function which decribes the correlation of the vortex induced force of the variable sections is unified, so that the function may be more applicable and stable.Finally, taken a three-span continuous steel box girder beam bridge as an engineering example, the application of the three-dimensional vortex induced vibration theory is explicit provided. Therefore, the conventional model test was conducted to analyse the vortex induced vibration of long span variable cross section beam bridge, and an aeroelastic model was carried out to confirm the validity of the results.