雙線鐵路橋墩早期裂縫的成因及對策
發(fā)布時間：2019-02-19 20:47
【摘要】：在混凝土的收縮及水化熱作用下，雙線橋墩結(jié)構(gòu)如果早期養(yǎng)護不到位，則容易在橋墩墩身出現(xiàn)早期裂縫，從而影響橋墩結(jié)構(gòu)的耐久性及安全性。 本文結(jié)合蘭新鐵路第二雙線某特大橋，對雙線橋墩早期裂縫的產(chǎn)生進行了實際探究及有限元分析。論文主要從以下幾個方面，作了深入的研究： （1）通過工程實際分析并結(jié)合相關(guān)資料，全面的的論述了雙線橋墩結(jié)構(gòu)早期裂縫形成的原因及其分類。論述了雙線橋墩早期裂縫形成的主要原因，即混凝土的收縮及水化熱影響。 （2）對雙線橋墩結(jié)構(gòu)施工現(xiàn)場混凝土的早期力學性能進行了測試，從而得到混凝土的軸心抗拉強度、彈性模量、極限拉伸及收縮變形隨齡期的變化規(guī)律，進而得到任意齡期時混凝土的抗拉強度計算公式。論述了混凝土結(jié)構(gòu)約束應(yīng)力的計算方法以及裂縫產(chǎn)生的力學條件。 （3）通過有限元軟件MIDAS FEA對雙線橋墩結(jié)構(gòu)建立有限元模型，進行有限元分析，得到混凝土收縮及水化熱作用效應(yīng)的發(fā)展規(guī)律以及產(chǎn)生的溫度及應(yīng)力變化情況。通過分析的得出，雙線橋墩結(jié)構(gòu)在靠近中線部位產(chǎn)生的拉應(yīng)力較大，中線兩側(cè)對稱位置拉應(yīng)力相等，離墩底越高，離中線越遠，拉應(yīng)力越小。通過對無槽橋墩與開槽橋墩結(jié)構(gòu)的有限元對比分析，，得到開槽后橋墩結(jié)構(gòu)同一位置的節(jié)點拉應(yīng)力小于無槽橋墩結(jié)構(gòu)，產(chǎn)生的最大拉應(yīng)力也減小。開槽后橋墩結(jié)構(gòu)的裂縫比率比無槽橋墩結(jié)構(gòu)大，更有利于避免早期裂縫的形成。 （4）通過改變開槽橋墩結(jié)構(gòu)墩身箍筋的布置方式、凹槽的形狀及尺寸等參數(shù)，對各種參數(shù)形式下的橋墩模型進行有限元分析。分別在混凝土凈保護層厚度為2cm、5cm、10cm、15cm、20cm的五種箍筋布置方式下，進行有限元模型對比分析，得出箍筋的改變對拉應(yīng)力的變化不大。分別將開槽橋墩凹槽的形狀假定為圓弧形、矩形、V形，經(jīng)過分析得知，圓弧形凹槽橋墩產(chǎn)生的拉應(yīng)力最小，V形凹槽橋墩最大。分別將開槽橋墩的凹槽尺寸假定為5cm、10cm、20cm，經(jīng)過分析得知，凹槽尺寸過大過小都會引起橋墩結(jié)構(gòu)拉應(yīng)力增大，必須選擇合理的尺寸。從而確定更加合理的箍筋布置方式以及最佳凹槽形狀及最佳凹槽尺寸，建議最佳凹槽形狀為圓弧形，最佳凹槽尺寸為10cm。
[Abstract]:Under the action of concrete shrinkage and hydration heat, if the early curing is not in place, the early cracks will easily appear in the pier body, which will affect the durability and safety of the pier structure. In this paper, combined with a large bridge on the second double track of Lanxin Railway, the practical exploration and finite element analysis of the early cracks of the pier of the double-track bridge are carried out. This paper mainly studies the following aspects: (1) through the analysis of engineering practice and combining with the relevant data, the causes and classification of the early cracks in the double-track pier structure are discussed comprehensively. This paper discusses the main causes of the early crack formation of double-track piers, that is, the shrinkage of concrete and the effect of hydration heat. (2) the early mechanical properties of concrete in the construction site of double-line piers are tested, and the variation of axial tensile strength, elastic modulus, ultimate tension and shrinkage deformation with age are obtained. Then the formula for calculating the tensile strength of concrete at any age is obtained. The calculation method of confined stress of concrete structure and the mechanical condition of crack are discussed. (3) the finite element model of double-track pier structure is established by finite element software MIDAS FEA, and the development rule of shrinkage and hydration heat effect of concrete and the variation of temperature and stress are obtained by finite element analysis. Through the analysis, it is concluded that the tensile stress of the double-line pier structure near the midline is larger, the symmetrical position of the midline is equal, the higher the pier bottom, the farther away from the central line, the smaller the tensile stress. Through the finite element analysis of the slotted pier and the slotted pier structure, it is concluded that the joint tensile stress of the slotted pier structure at the same position is smaller than that of the slotted pier structure, and the maximum tensile stress is also reduced. The crack ratio of the slotted pier structure is larger than that of the slotted pier structure, which is more helpful to avoid the formation of early cracks. (4) the finite element analysis of pier model under various parameter forms is carried out by changing the layout of stirrups of pier body of slotted pier structure, the shape and size of groove and so on. When the thickness of concrete net cover is 2 cm, 5 cm, 10 cm, 15 cm and 20 cm respectively, the finite element model is compared and analyzed, and it is concluded that the change of stirrups has little effect on the tensile stress. The shape of groove of slotted pier is assumed to be arc shape, rectangle shape and V shape, respectively. The analysis shows that the tension stress of circular arc groove pier is the minimum, and that of V groove pier is the largest. The slot size of the slotted pier is assumed to be 5 cm ~ 10 cm ~ (-1) 20 cm respectively. The analysis shows that too large and too small of the groove size will cause the tensile stress of the pier to increase, and a reasonable size must be selected. Therefore, the more reasonable arrangement of stirrups, the optimum groove shape and the optimum groove size are determined. The optimum groove shape is arc and the optimum groove size is 10 cm.
【學位授予單位】：蘭州交通大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：U445.7
本文編號：2426865
[Abstract]:Under the action of concrete shrinkage and hydration heat, if the early curing is not in place, the early cracks will easily appear in the pier body, which will affect the durability and safety of the pier structure. In this paper, combined with a large bridge on the second double track of Lanxin Railway, the practical exploration and finite element analysis of the early cracks of the pier of the double-track bridge are carried out. This paper mainly studies the following aspects: (1) through the analysis of engineering practice and combining with the relevant data, the causes and classification of the early cracks in the double-track pier structure are discussed comprehensively. This paper discusses the main causes of the early crack formation of double-track piers, that is, the shrinkage of concrete and the effect of hydration heat. (2) the early mechanical properties of concrete in the construction site of double-line piers are tested, and the variation of axial tensile strength, elastic modulus, ultimate tension and shrinkage deformation with age are obtained. Then the formula for calculating the tensile strength of concrete at any age is obtained. The calculation method of confined stress of concrete structure and the mechanical condition of crack are discussed. (3) the finite element model of double-track pier structure is established by finite element software MIDAS FEA, and the development rule of shrinkage and hydration heat effect of concrete and the variation of temperature and stress are obtained by finite element analysis. Through the analysis, it is concluded that the tensile stress of the double-line pier structure near the midline is larger, the symmetrical position of the midline is equal, the higher the pier bottom, the farther away from the central line, the smaller the tensile stress. Through the finite element analysis of the slotted pier and the slotted pier structure, it is concluded that the joint tensile stress of the slotted pier structure at the same position is smaller than that of the slotted pier structure, and the maximum tensile stress is also reduced. The crack ratio of the slotted pier structure is larger than that of the slotted pier structure, which is more helpful to avoid the formation of early cracks. (4) the finite element analysis of pier model under various parameter forms is carried out by changing the layout of stirrups of pier body of slotted pier structure, the shape and size of groove and so on. When the thickness of concrete net cover is 2 cm, 5 cm, 10 cm, 15 cm and 20 cm respectively, the finite element model is compared and analyzed, and it is concluded that the change of stirrups has little effect on the tensile stress. The shape of groove of slotted pier is assumed to be arc shape, rectangle shape and V shape, respectively. The analysis shows that the tension stress of circular arc groove pier is the minimum, and that of V groove pier is the largest. The slot size of the slotted pier is assumed to be 5 cm ~ 10 cm ~ (-1) 20 cm respectively. The analysis shows that too large and too small of the groove size will cause the tensile stress of the pier to increase, and a reasonable size must be selected. Therefore, the more reasonable arrangement of stirrups, the optimum groove shape and the optimum groove size are determined. The optimum groove shape is arc and the optimum groove size is 10 cm.
【學位授予單位】：蘭州交通大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：U445.7
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