双线铁路桥墩早期裂缝的成因及对策
发布时间：2019-02-19 20:47
【摘要】：在混凝土的收缩及水化热作用下，双线桥墩结构如果早期养护不到位，则容易在桥墩墩身出现早期裂缝，从而影响桥墩结构的耐久性及安全性。 本文结合兰新铁路第二双线某特大桥，对双线桥墩早期裂缝的产生进行了实际探究及有限元分析。论文主要从以下几个方面，作了深入的研究： （1）通过工程实际分析并结合相关资料，全面的的论述了双线桥墩结构早期裂缝形成的原因及其分类。论述了双线桥墩早期裂缝形成的主要原因，即混凝土的收缩及水化热影响。 （2）对双线桥墩结构施工现场混凝土的早期力学性能进行了测试，从而得到混凝土的轴心抗拉强度、弹性模量、极限拉伸及收缩变形随龄期的变化规律，进而得到任意龄期时混凝土的抗拉强度计算公式。论述了混凝土结构约束应力的计算方法以及裂缝产生的力学条件。 （3）通过有限元软件MIDAS FEA对双线桥墩结构建立有限元模型，进行有限元分析，得到混凝土收缩及水化热作用效应的发展规律以及产生的温度及应力变化情况。通过分析的得出，双线桥墩结构在靠近中线部位产生的拉应力较大，中线两侧对称位置拉应力相等，离墩底越高，离中线越远，拉应力越小。通过对无槽桥墩与开槽桥墩结构的有限元对比分析，，得到开槽后桥墩结构同一位置的节点拉应力小于无槽桥墩结构，产生的最大拉应力也减小。开槽后桥墩结构的裂缝比率比无槽桥墩结构大，更有利于避免早期裂缝的形成。 （4）通过改变开槽桥墩结构墩身箍筋的布置方式、凹槽的形状及尺寸等参数，对各种参数形式下的桥墩模型进行有限元分析。分别在混凝土净保护层厚度为2cm、5cm、10cm、15cm、20cm的五种箍筋布置方式下，进行有限元模型对比分析，得出箍筋的改变对拉应力的变化不大。分别将开槽桥墩凹槽的形状假定为圆弧形、矩形、V形，经过分析得知，圆弧形凹槽桥墩产生的拉应力最小，V形凹槽桥墩最大。分别将开槽桥墩的凹槽尺寸假定为5cm、10cm、20cm，经过分析得知，凹槽尺寸过大过小都会引起桥墩结构拉应力增大，必须选择合理的尺寸。从而确定更加合理的箍筋布置方式以及最佳凹槽形状及最佳凹槽尺寸，建议最佳凹槽形状为圆弧形，最佳凹槽尺寸为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.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：U445.7
本文编号：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.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：U445.7
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