Study On Normal Wind Characteristics Over Bridge Sites With Typical Mountainous Terrain

When flowing through mountainous terrain,wind will be influenced and a complex terrain wind field will be formed,which differs from the wind field on flat ground and makes the wind resistance design of large-span bridges in mountainous terrain differ from that on flat ground.In order to provide a valuable parameter for the wind resistance design of long-span bridges in mountainous terrain,it is necessary to study the wind field characteristics over bridge sites with typical mountainous terrain,especially the wind blow along the canyon,which is also very important for the determination for the basic design wind speed of mountainous-valley bridges.The basic design wind speed is generally revised by the basic wind speed.However,it is difficult to define accurately in practical engineering application for the wind speed correction coefficient of the present provisions.In addition,due to the lack of the research on field measurements of wind characteristics of large-span bridges with high pylons in mountainous terrain,further research on the characteristics of wind field has a great significance on the wind resistance design of long-span bridges in mountainous terrain.The main research works are as follows:(1)The present research over mountainous-valley terrain was conducted to investigate comprehensively with wind tunnel tests of terrain model,field measurements and CFD simulations.Moreover,a review of the basic design wind speed of mountainous-valley bridges was given.(2)In order to study the wind field characteristics over bridge sites,the characteristics over large-span bridge sites in mountainous terrain were investigated adequately.Three test conditions of typical two-dimensional hill models were designed.Wind tunnel tests and CFD simulations were used to analyze the characteristics of wind field of the three test conditions.There was a great speed-up effect at the top and lateral slope of the hills.The speed-up ratio of the intermediate position was less than that of both ends of the position at the same height.The equivalent reference heights of the basic design wind speed of wind tunnel tests were compared with that of the provisions,which were calculated by the equivalent principle of transverse wind loads.(3)Field measurement and analysis of wind characteristics of the Chishi Bridge during construction stages were carried out,where Chishi Bridge is a large-span cable-stayed bridge located in Chenzhou,Hunan,China.The wind characteristic parameters at deck level and pylon top during observation period were analyzed,including the mean wind speeds,wind directions,wind attack angles and turbulence intensities.The results showed that wind attack angles changed within a rather wide range when the wind blew from the north,while the wind attack angles varied within a narrow range when the wind came from the south.(4)Wind environment for the flow around the large region over the Chishi Bridge site with complex terrain was numerically simulated.The simulated results were compared with results of field measurement.The simulated results were also compared with results of wind tunnel tests of typical two-dimensional hill models based on the equivalent reference heights calculated by the wind speed of monitoring points at deck level.The simulated results over the Chishi Bridge site agreed well with results of field measurement and wind tunnel tests of typical two-dimensional hill models.