山区窄式悬索桥加劲梁断面气动选型数值分析

发布时间：2019-02-16 09:49

【摘要】：大跨径悬索桥的几何非线性特点决定了其结构很容易受活荷载作用影响,如车道荷载、风荷载等动力荷载。因此,对于大跨径结构的桥梁,动力性能的分析是必要的,也是设计中的关键步骤。本文以地处甘肃省永靖县内的刘家峡大桥为工程背景,围绕桥梁主梁断面气动分析,在已有的研究工作上,采用以理论分析为基础,利用风洞试验和有限元数值模拟方法对桥梁主梁断面气动性能进行了局部到整体的分析研究。主要工作及研究结论有:(1)归纳整理了刘家峡大桥加劲梁节段风洞试验数据,得出三分力系数随折减风速的变化规律以及8个气动导数,并为后面数值分析提供对比条件。通过风洞节段模型试验测定三分力系数,绘制三分力系数随风攻角变化的曲线图,并分析气动三分力系数与颤振稳定性能之间的关系,从而通过桥梁不同断面的静三分力系数,对其结构断面颤振稳定性进行快速评价和判定。桥梁断面的气动力参数对于桥梁设计选型,以及桥梁结构的安全性和经济性具有重要意义。(2)为了更好的说明桥梁断面气动选型的优劣性,在已有的桥梁主梁断面中选取与刘家峡大桥主梁横截面尺寸相似的钢箱式主梁,其主梁净宽15.6m,高2m。利用Midas FEA中的CFD方法建立主梁断面气动数值模型,研究在几何条件相似的情况下,给定同样的边界条件和分析工况,其断面气动性能的优劣。从提取的三分力系数以及随时间变化的压力场分布图中,综合分析对比,钢桁式加劲梁断面气动性能要好于钢箱式加劲梁。(3)仅从加劲梁节段断面气动数值模拟来说明整个悬索桥的抗风性能是片面的,不完全的。因此建立悬索桥三维空间有限元动力模型,将两种不同截面形式的加劲梁归于桥梁整体结构中,添加边界条件,设定分析工况,对悬索桥整体抗风性能进行分析计算,提取前六阶振动模态。选取桥梁中跨跨中加劲梁作为研究对象,整理分析在风速逐级加载的过程中,加劲梁竖向、侧向以及扭转位移值,并以直观的曲线图列出。在桥梁整体分析中得出,结合刘家峡大桥结构特点,两种截面形式主梁的悬索桥均满足其抗风要求,但选用钢桁式截面加劲梁的抗风性能更强,更适合刘家峡大桥自身特色。(4)在数值模拟桥梁断面气动计算中,有限元Midas FEA中只能进行二维CFD分析,而钢桁式加劲梁是多个杆件组合非闭合式梁,若要确切、精准的模拟该主梁在风场环境中的气动性能,需要一个三维空间模型。目前在ANSYS中有Workbench、FLOTRAN等模块可以进行空气流场的仿真模拟,在工程领域也有很好的实际应用。在数据研究分析中均考虑了大跨径悬索桥结构的受力特点以及刘家峡大桥桥址所处地理环境、季节性气候的影响。加之该桥是西北地区首座大跨径、桥面最窄、国内首个采用大直径钢管混凝土作为桥塔构件等独具的结构特点。
[Abstract]:The geometric nonlinearity of long-span suspension bridge determines that its structure is easily affected by live load such as driveway load wind load and other dynamic loads. Therefore, the analysis of dynamic performance is necessary and a key step in the design of long span bridges. Taking the Liujiaxia Bridge, located in Yongjing County, Gansu Province, as the engineering background, around the aerodynamic analysis of the main girder section of the bridge, the existing research work is based on the theoretical analysis. Using wind tunnel test and finite element numerical simulation method, the aerodynamic performance of bridge girder section is studied locally to integrally. The main works and conclusions are as follows: (1) the wind tunnel test data of the stiffened girder section of the Liujiaxia Bridge are summarized, and the variation law of the three-point force coefficient with the reduced wind speed and the eight aerodynamic derivatives are obtained, and the comparison conditions for the latter numerical analysis are provided. The three-point force coefficient was measured by wind tunnel segment model test, and the curve of variation of three-point force coefficient with wind attack angle was plotted. The relationship between aerodynamic three-point force coefficient and flutter stability performance was analyzed, and then the static three-point force coefficient of different sections of the bridge was obtained by analyzing the relationship between aerodynamic three-point force coefficient and flutter stability performance. The flutter stability of the structure section is evaluated and judged quickly. The aerodynamic parameters of the bridge section are of great significance for the design and selection of the bridge, as well as the safety and economy of the bridge structure. (2) in order to better explain the advantages and disadvantages of the aerodynamic selection of the bridge section, The steel box girder with the same cross section size as the main girder of Liujiaxia Bridge is selected from the section of the existing main girder. The net width of the main girder is 15.6 m and the height is 2 m. The aerodynamic numerical model of the main beam section is established by using the CFD method in Midas FEA, and the aerodynamic performance of the main beam section is studied under the condition of similar geometric conditions and given the same boundary conditions and analytical conditions. From the extracted three-point force coefficient and pressure field distribution map with time variation, comprehensive analysis and comparison, The section aerodynamic performance of steel truss stiffened beam is better than that of steel box stiffened beam. (3) the aerodynamic numerical simulation of stiffened girder section shows that the wind resistance of the whole suspension bridge is one-sided and incomplete. Therefore, the three-dimensional finite element dynamic model of suspension bridge is established, and two stiffened beams with different cross-section are put into the whole structure of the bridge. Boundary conditions are added, and the analysis conditions are set up, and the overall anti-wind performance of the suspension bridge is analyzed and calculated. The first six vibration modes are extracted. The vertical, lateral and torsional displacement values of the stiffened beam in the middle span of the bridge are analyzed in the process of wind speed step by step loading. In the whole analysis of the bridge, it is concluded that the suspension bridges with two kinds of cross-section main beams can meet the requirements of wind resistance combined with the structural characteristics of Liujiaxia Bridge, but the wind-resistant performance of stiffened beams with steel truss section is stronger than that of steel truss stiffened beams. It is more suitable for the Liujiaxia Bridge itself. (4) in the numerical simulation of the cross-section aerodynamic calculation of the bridge, the finite element Midas FEA can only carry out two-dimensional CFD analysis, while the steel truss stiffening beam is a multi-member composite non-closed beam. A three-dimensional model is needed to accurately simulate the aerodynamic performance of the main beam in the wind field. At present, there are some modules such as Workbench,FLOTRAN in ANSYS to simulate the air flow field. In the analysis of the data, the bearing characteristics of the long-span suspension bridge structure and the influence of the geographical environment and seasonal climate on the site of the Liujiaxia Bridge are taken into account. In addition, the bridge is the first long span in Northwest China with the narrowest deck, and the first concrete filled steel tube (CFST) with large diameter is used as the tower member in China.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U448.25

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