【摘要】：大跨徑懸索橋的幾何非線性特點決定了其結(jié)構(gòu)很容易受活荷載作用影響,如車道荷載、風荷載等動力荷載。因此,對于大跨徑結(jié)構(gòu)的橋梁,動力性能的分析是必要的,也是設(shè)計中的關(guān)鍵步驟。本文以地處甘肅省永靖縣內(nèi)的劉家峽大橋為工程背景,圍繞橋梁主梁斷面氣動分析,在已有的研究工作上,采用以理論分析為基礎(chǔ),利用風洞試驗和有限元數(shù)值模擬方法對橋梁主梁斷面氣動性能進行了局部到整體的分析研究。主要工作及研究結(jié)論有:(1)歸納整理了劉家峽大橋加勁梁節(jié)段風洞試驗數(shù)據(jù),得出三分力系數(shù)隨折減風速的變化規(guī)律以及8個氣動導數(shù),并為后面數(shù)值分析提供對比條件。通過風洞節(jié)段模型試驗測定三分力系數(shù),繪制三分力系數(shù)隨風攻角變化的曲線圖,并分析氣動三分力系數(shù)與顫振穩(wěn)定性能之間的關(guān)系,從而通過橋梁不同斷面的靜三分力系數(shù),對其結(jié)構(gòu)斷面顫振穩(wěn)定性進行快速評價和判定。橋梁斷面的氣動力參數(shù)對于橋梁設(shè)計選型,以及橋梁結(jié)構(gòu)的安全性和經(jīng)濟性具有重要意義。(2)為了更好的說明橋梁斷面氣動選型的優(yōu)劣性,在已有的橋梁主梁斷面中選取與劉家峽大橋主梁橫截面尺寸相似的鋼箱式主梁,其主梁凈寬15.6m,高2m。利用Midas FEA中的CFD方法建立主梁斷面氣動數(shù)值模型,研究在幾何條件相似的情況下,給定同樣的邊界條件和分析工況,其斷面氣動性能的優(yōu)劣。從提取的三分力系數(shù)以及隨時間變化的壓力場分布圖中,綜合分析對比,鋼桁式加勁梁斷面氣動性能要好于鋼箱式加勁梁。(3)僅從加勁梁節(jié)段斷面氣動數(shù)值模擬來說明整個懸索橋的抗風性能是片面的,不完全的。因此建立懸索橋三維空間有限元動力模型,將兩種不同截面形式的加勁梁歸于橋梁整體結(jié)構(gòu)中,添加邊界條件,設(shè)定分析工況,對懸索橋整體抗風性能進行分析計算,提取前六階振動模態(tài)。選取橋梁中跨跨中加勁梁作為研究對象,整理分析在風速逐級加載的過程中,加勁梁豎向、側(cè)向以及扭轉(zhuǎn)位移值,并以直觀的曲線圖列出。在橋梁整體分析中得出,結(jié)合劉家峽大橋結(jié)構(gòu)特點,兩種截面形式主梁的懸索橋均滿足其抗風要求,但選用鋼桁式截面加勁梁的抗風性能更強,更適合劉家峽大橋自身特色。(4)在數(shù)值模擬橋梁斷面氣動計算中,有限元Midas FEA中只能進行二維CFD分析,而鋼桁式加勁梁是多個桿件組合非閉合式梁,若要確切、精準的模擬該主梁在風場環(huán)境中的氣動性能,需要一個三維空間模型。目前在ANSYS中有Workbench、FLOTRAN等模塊可以進行空氣流場的仿真模擬,在工程領(lǐng)域也有很好的實際應(yīng)用。在數(shù)據(jù)研究分析中均考慮了大跨徑懸索橋結(jié)構(gòu)的受力特點以及劉家峽大橋橋址所處地理環(huán)境、季節(jié)性氣候的影響。加之該橋是西北地區(qū)首座大跨徑、橋面最窄、國內(nèi)首個采用大直徑鋼管混凝土作為橋塔構(gòu)件等獨具的結(jié)構(gòu)特點。
[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.
【學位授予單位】：蘭州交通大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：U448.25

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