Study On Aerodynamic Admittance Function Of Bridge And Its Application

As the span length of long span bridges increases, buffeting response caused by fluctuation components of atmosphere turbulence become one of the most important factors endangering the structure safety. Describing the buffeting gust load properly is an important section to predict the buffeting response. Aerodynamic admittance function, which could reflect the transfer process between fluctuation components of turbulence and gust loads of structure, is the key factor to determine the gust load. Either Sears function of airfoil section or no considering aerodynamic admittance usually used in bridge buffeting computation now is not suitable actually.Based on unsteady aerodynamic gust load model, identification method of six aerodynamic admittance functions which could reflect influence of the fluctuation components of turbulence on the gust load components are set up in the paper. Combined with wind tunnel test, unsteady gust forces of truss section model are measured by high frequency dynamic balance as well as different chord-thickness ratio section models of flat box section at different attack angle. Accordingly, characteristic of aerodynamic admittance function are obtained. Finally, buffeting responses of two long-span suspension bridges are calculated to investigate the feasibility of the aerodynamic admittance measured in wind tunnel. The research works are mainly concerned with the following aspects:Firstly, aerodynamic gust load model suitably for bridge section in turbulent is studied. And the unsteady gust load model included six aerodynamic admittance functions which could reflect influence degree of the fluctuation components of turbulence on the gust load components is established, as well as the physical significance of six aerodynamic admittance is explicitly defined.Secondly, the usage of aerodynamic admittance functions in bridge structure are investigate, and the deficit of Sears function based on airfoil theory used generally in bridge buffeting prediction is pointed out. Based on unsteady gust load model, the identification method of all the six aerodynamic admittance functions is put forward.Thirdly, four flat box section models with different chord-to-thickness ratio and a truss section model are designed. Combined with high frequency dynamic balance technology, the character and variety law of aerodynamic admittance function of flat box and truss section models are studied in wind tunnel. Some important conclusions are obtained. By numerical simulation, the formulas of aerodynamic admittance functions of flat box and truss section, which could be used in calculating three components of gust load, are proposed respectively.Finally, by the buffeting predictions of Zhu-River Huangpu suspension bridge with main span 1108m and Baling-River suspension bridge with main span 1088m, the feasibility of aerodynamic admittance functions identified by unsteady theory is investigated. By the research result, the method and the unsteady identification theory of aerodynamic admittance function are sound and feasible, which could reflect the influence the components of turbulent on the three components of gust load properly. And the test aerodynamic admittance could be used in buffeting prediction of actual bridge conveniently. The research method could be suited for the identification of aerodynamic admittance function of both long-span flat box girder and truss structure stiffened girder.