Wind-Tunnel Experimental Investigations On Aerodynamic Characteristics Of Typical Bridge Decks

The wind-resistance performance of long-span bridge has become a controlling factor under the construction process and could influence the operational safety. The girder section aerodynamic has become an important research issue in long-span bridge field.Wind tunnel test is a very important and irreplaceable means in studying the structure’s aerodynamic characteristics. This paper based on two typical sections, bluff girder section and streamline girder section, making wind resistance analysis and experimental research. The main contents are listed as follows:(1) Pressure and vibration measurement tests were performed on the two typical section model of main girder. Study the tri-component force coefficient under different conditions, summarize the change rules and analyze the reasons that generate the changes. Making analysis of the skewness and kurtosis about the surface pressure signal in a stationary state and different conditions of the two types cross section. Figuring out its change rules and changing reasons during the construction phase and completion phase. Experimental data show that the torque coefficient and lift coefficient absolute value of construction state are greater than the corresponding value of completetion state; The resistance coefficient of completetion state is significantly greater than the construction state; The torque coefficient of streamlined section is greater than the blunt body section. Compared with the construction state, the skewness in completetion state of the two sections are appeared big deviation in each attack angle; The signal of the model latter part showed strong non-Gaussian; The streamlined section showing relatively good Gaussian; The greater the angle of attack, the appearance of non-Gaussian is stronger.(2) Doing researching on system damping ratio and signal’s emission and convergence rate of different working conditions and soft flutter time history responses as well as the steady amplitude of two types girder section model under typical conditions. Explore the vibration characteristics of the model in the wind field and the influence of airflow on the vibration characteristic. Analysis found that as wind speed increased, the steady-state oscillation amplitude is increasing, the time to achieve the desired steady state amplitude is shorter; In the same conditions, when the soft flutter occurs, no matter what form of initial excitation is applied to the system, the final twist amplitude of the steady-state are same.(3) Analysis of the distribution of surface pressure and the change rules of pressure coefficient mean and standard of the model in static state and soft flutter state were performed. To explore the static and pulsating effects of airflow on the model surface. Compare the distribution characteristics of model surface wind pressure under different state, and the effect of vibration on the model surface wind pressure. The tests show that compared with bluff section, the surface pressure distribution of streamlined section scroll less frequently attached and detached appearance; The roof pressure coefficients variance of two sections were moved downstream as the measuring points, showed a trend of first increases then decreases to a smooth, peak moves to downstream as the angle attack change from negative to positive; Under the soft flutter state, the surface pressure coefficient of two sections increase with the increase of wind speed; Due to the negative stiffness of pneumatic, the modal frequencies is lower than the torsional natural frequency under soft flutter state.