Research Of Wind Characteristic Parameters And Wind-induced Vibration Of Long Span Bridge With Truss Girder In Mountainous Area

Wind resistance of bridges, located in canyon and mountainous area, has been the hotspot and difficulty in current wind engineering research. It is a multi-disciplines research topics related to wind characteristics, bridge structures and wind resistance optimization method. Although there are some wind resistance research and discussion regarding to bridges in mountainous area at home and abroad, there are few literature and datum about the actual measured weather, wind characteristics and wind resistance design. This dissertation takes the long span truss suspension bridge, Ba-Ling-He bridge in Guizhou province, China, as an example, and systematically investigates the canyon wind characteristics of mountainous area and wind resistance problem of long span truss suspension bridge. The main contents include the following,(1) The wind characteristics at Ba-Ling-He bridge site are computed numerically through a commercial code FLUENT. The study is focused on the wind field distribution at the bridge site. The relationship between wind speed components at check point and wind speed of inlet boundary can be described by introducing a dimensionless parameter, wind speed amplification coefficient. Through wind tunnel testing of scaled terrain model of Ba-Ling-He bridge site, the turbulence wind circumstance in canyon is investigated thoroughly. The spatial distribution of wind field at mountain area is discussed from characteristics of three aspects, mean wind, gusty wind and particular mountainous wind.(2) The wind resistance design speed of bridge at canyon in a mountainous area can hardly been accurately estimated due to lack of filed measurement. Based on the previous literatures, the establishment of'virtual standard meteorological station'is dissucssed and the inverse distance weighted wind speed interpolation method is improved. A method is proposed to calculate the design wind speed by defining two interpolation factors, displacement factor and mountain shelter effect factor, and introducing wind speed modification of the height above sea level. An empirical formula is suggested to calculate the basic wind speed in a canyon of a mountainous area. The formula is validated by several examples and is high accurate and practical in prediction of the design speed in a mountainous area.(3) The design principle is discussed for the full aeroelastic model of bridge with stiffened truss girder. And the structural dynamic properties are calculated by the FEM of full bridge by taking Ba-Ling-He bridge and Guo-Zi-Gou bridgeas examples. Based on the design experience of full aeroelastic model of Akashi-Kaikyo Bridge, the spring shape 'V' is replaced by the other spring shape 'U', which is used to connect the sections to simulate stiffness of the stiffened truss girder. The spring shape 'U' is proved to be more suitable for full aeroelastic modeling of long-span bridge with truss girder. Each parameters of the 'U' type spring is discussed to show the effect to stiffness of girder.(4) Upon reviewing the flutter analysis theory, a computational code by using the state space method is written to analyze 3d flutter of the Ba-Ling-He bridge. The aerodynamic optimization for the truss girder of Ba-Ling-He bridge are studied by section model wind tunnel test. It is the first application for the aerodynamic wing in actual bridge. After analyzing and testing the effect aerodynamic means on flutter stability, an optimal configuration of deck is finally proposed, which is the combination of the central slot and aerodynamic wing. The flutter suppression mechanism of aerodynamic wing is analyzed by studying total torsional damping ratio of section model system varying with wind speed.(5) The aerodynamic admittance function of stiffened truss girder is investigated by sectional model wind tunnel testing. This dissertation introduces the test methodology and the identification method of aerodynamic admittance function, and discusses three types of aerodynamic admittance functions under different attack angles and wind speeds. Then, a fitting formula is proposed for aerodynamic admittance function of stiffened truss girder by using experimental results. The buffeting responses are analyzed in frequency domain by taking the Ba-Ling-He bridge and Guo-Zi-Gou bridge as example. The good agreement between buffeting response tested and calculated ones proves validity of the testing method for aerodynamic admittance function of the truss section and fitting formulae.(6)Finally, as an example, the wind induced response of Ba-Ling-He bridge is tested through full bridge aeroelastic model in wind tunnel. The wind induced response is systematically analyzed to obtain internal forces induced by the turbulence wind. Those give essential reference to bridge wind resistance design.