Test Research On Aerodynamic Admittance Of A Long Span Cable-stayed Bridge Girder Section

Large-span cable-stayed bridges will inevitably occur buffeting due to light weight, high flexibility and low damping. Buffeting of the bridge structure is mainly caused by atmospheric turbulent components. And excessive bridge buffeting response induced by turbulence will cause local fatigue failure to the structure, pedestrian uncomfortableness as well as traffic unsafe, and even may engender the structure result in direct damage. Therefore, proper evaluation of buffeting response of bridges is very important, and the aerodynamic admittance plays a crucial role in the analysis of bridge buffeting response. In order to study the aerodynamic admittance of streamlined steel-box girder cross-section used by a large-span cable-stayed bridge, this thesis utilizes sectional model wind tunnel tests and theoretical analysis to research the aerodynamic admittance of streamlined steel-box girder cross-section. The main contents include the following:1. Reviewed and summarized the results of previous studies of aerodynamic admittance, and crystallized the definition and mechanical significance of aerodynamic admittance. Introduced three theories to identify the aerodynamic admittance of bridge cross-section and experimental measurement technique for aerodynamic admittance, and then presented the testing program of this thesis, which provide the basis for implementation of wind tunnel aerodynamic admittance tests.2. Detailed introduced the atmospheric boundary layer and the statistical parameters describing characteristics of atmospheric turbulence. Established a grid turbulence field for wind tunnel test, and measured its main features and presented the test results of the turbulence intensity and wind speed power spectrum. Test data analysis shows that the establishment of the grid turbulence field meets the test requirements of aerodynamic admittance.3. For the cross-section models of recommended and alternative schemes of a cable-stayed bridge girder which are respectively closed and open streamlined steel box girder, we used the established grid turbulence field, as well as the high-frequency balance and hot-wire anemometer and other instruments to measure the aerodynamic admittance of the models by equivalent aerodynamic admittance method. And the test results were analyzed and the aerodynamic admittance curve of the two sections was fit out. Also then systematically studied the impact of wind speed, attack angle of wind and railings in identifying the aerodynamic admittance, and draw a number of important results and conclusions.4. Introduced the buffeting force calculation model, and then established frequency domain analysis methods of buffeting based on testing aerodynamic admittance. And took a large-span cable-stayed bridge as example, calculated its buffeting response. At the same time compared to the wind tunnel test results of full-bridge aeroelastic model. And obtained the conclusion that frequency domain analysis of buffeting which based on testing aerodynamic admittance can get proper results.