Study On Stability Of Large Span Concrete Arch Bridges Based On Wind Field Characteristic In Canyon Terrain

With the rapid development of China’s economy and the advancement of science and technology,achieving coordinated regional development has become a top priority.The emergence of new materials and advanced construction techniques has led to the development of large span bridges with high span,light mass and low stiffness,and the sensitivity to wind has gradually increased,so the wind stability of large span bridges is attracting more and more attention..The study of the wind characteristics at the bridge level is a prerequisite for the wind resistance design of bridges,and the wind environment in the western mountainous regions of China is very complex,and the understanding and research is still relatively superficial,which seriously affects the accuracy and safety of the wind resistance design of bridges.In this thesis,the wind characteristics of a canyon arch bridge in the western mountainous region of China are studied,and CFD numerical simulation technology is used to investigate the wind characteristics.Based on this,a stability study was carried out for the arch bridge across the canyon.The main work and results are as follows:(1)Ansys Fluent simulation software was used to conduct a CFD numerical simulation study on the wind field characteristics of a one-span gorge arch bridge site in the western mountainous region.The spatial distribution of mean wind speed,wind angle of attack,wind deflection angle,wind speed profile and turbulence intensity along the main girder at the bridge site were obtained;the mechanism of the influence of the complex gorge topography on the wind field characteristics was analysed,and the wind speed amplification factor was introduced.(2)A new terrain model acquisition method is presented in detail to address the problems of difficulty and lack of accuracy in acquiring complex mountain terrain models.The method is based on SRTM data and uses the professional terrain software Global Mapper to crop out the 3D terrain scatter cloud map of the study area,and uses the reverse engineering software Geomagic to perform point cloud processing and surface fitting to complete the final terrain modelling.This method is convenient and fast,and can obtain a terrain model with high accuracy,which can be used as a reference for similar studies.In order to solve the problem of the lack of meteorological data in the bridge site area of the canyon and the difficulty of calculating the basic wind speed at the entrance of the domain,this thesis adopts the "virtual standard meteorological station method" and obtains the basic wind speed at the entrance height of the bridge by fitting the relationship curve between the basic wind speed and the altitude of the nearby districts and counties.(3)The finite element analysis software Midas/civil was used to establish a finite element model of the whole bridge and to analyse the dynamic characteristics of the arch bridge in the completed state.The inherent frequency and self-oscillation period of the bridge were obtained,based on which the lateral stability and torsional stability of the bridge in the completed state were analysed to provide a basis for subsequent research.(4)Linear buckling analysis and static wind response analysis were carried out for four typical construction stages of concrete arch bridges,namely,suspended arch foot,maximum cantilever,single-rib closure and single-rib bare arch,under static wind loads.The static wind instability modalities and critical safety coefficients of the structure in each construction stage were obtained,and the static wind instability characteristics of the structure were investigated;the displacement,internal force and stress response of the structure in each construction stage were obtained.The maximum combined stresses in the single-rib closure state exceeded the design value of the axial compressive strength of the concrete,which no longer met the code requirements;the setting of the cables during the construction of the arch bridge was optimised in terms of the horizontal setting angle of the cables and the initial tension.