Research On Bridge Wind Characteristics Based On Canyon Terrain Parameters

With the increasing emphasis on infrastructure construction in the central and western regions,in order to improve the transportation capacity of the central and western regions,it is necessary to build a corresponding transportation system,and bridges play an important role in building transportation networks.Due to the high and low terrain in the western region,the bridges built need to cross mountains and valleys,so more and more cable-stayed bridges or high-pier continuous rigid frame bridges have become the first choice,and the wind-resistant design of cable-stayed bridges,which are wind-sensitive structures,is particularly complex in this complex terrain.Since the existing design specifications for bridge wind resistance mainly aim at the four types of sites,the reference basis for the design wind parameters of mountainous terrain is not given,and the existing research is carried out based on a specific project,which does not have a standardized reference value for the wind resistance design of the same type of bridge.Therefore,it is necessary to carry out the wind field characteristics of mountainous terrain bridge based on terrain parameters.In this paper,the canyon terrain of a double-tower single cable plane cable-stayed bridge in the western mountainous area is taken as the research object,and the wind field characteristics of such terrain are studied by means of "physical wind tunnel" and " numerical wind tunnel ".Firstly,the existing bridge wind resistance design specifications are studied and analyzed.It is found that the 2018 version of the highway bridge wind resistance design specification adds terrain condition coefficient,terrain type conversion and wind speed height correction coefficient to the 2004 version of the specification when calculating the design reference wind speed at the benchmark height of the bridge component.The existing research results have less research on this parameter,so this parameter is selected as the research object.Secondly,the numerical simulation is carried out for the actual terrain of the bridge wind field,and the applicability and feasibility of the numerical simulation method for such terrain are verified by combining the results of the previous wind tunnel test of the research group.On this basis,how to improve the accuracy of "numerical wind tunnel"in the simulation of wind field characteristics at this kind of bridge site is discussed from the four factors of grid division method,grid type,grid density and turbulence model.It is found that the accuracy of SST k-ωturbulence model in this case is higher when ICEM CFD preprocessor is used,and the resolution is 30 m×30 m hexahedral grid.At the same time,in order to verify the influence of the existence of the real bridge structure on the wind field characteristics of the bridge site in complex terrain,the wind field characteristics with and without the real bridge structure are analyzed based on the above numerical wind tunnel research results.Compared with the wind tunnel test results,it is found that the influence of the existence of the real bridge structure on the wind field characteristics can be ignored compared with the whole bridge site wind field.Therefore,after the real bridge structure is not considered in this paper,the simplified model is adopted to carry out the calculation of the wind field characteristics of multiple terrain parameters(valley length,valley width and mountain height).The wind speed and pressure contours on the mountain surface,as well as the variation law of the key parameters required for wind resistance design such as wind speed and turbulence intensity,are obtained.By comparing the results with the existing specifications,it is found that the valley width in the terrain Parameters has a great influence on the spatial distribution characteristics of the wind field.Finally,based on the above research results,this paper gives the calculation formula of the design basic wind speed at the reference height of the main force components of the cable-stayed bridge with the change of terrain parameters under the same type of site conditions,and strives to provide reference for the wind resistance design of cable-stayed bridges under the same type of site conditions.