岩基上扩展基础承载性能的有限元及塑性铰理论分析
发布时间：2018-10-26 14:47
【摘要】：岩石地基的刚度大、承载力高、变形小的特点,使岩石地基上扩展基础的基底反力和受力特性与土质地基有所不同。按现行规范进行岩石地基上独立基础设计存在一些不合理之处。本文主要利用有限元软件研究分析岩石地基弹性模量、基础跨高比、基础底部配筋对基础截面剪力、基底反力分布、基础裂缝、基础极限承载力的影响。其主要工作和成果如下:(1)利用有限元软件计算得到基础不同截面剪力大小,发现在基础中心到柱边缘范围内基础截面剪力值近似呈线性增大,而在柱边缘到基础边缘范围内基础截面剪力值呈非线性减小,减小的速度由快变慢最后趋于平缓。剪力最大值出现在柱与基础交接处所在截面。相同荷载作用下,随着岩石的弹性模量增大、基础的跨高比减小,基础截面剪力最大值减小。(2)分析有限元得到的基底反力结果可以发现岩石地基上柱下独立基础基底反力分布呈现高度的非线性。基底反力分布总体趋势从基础底部中心向基础两边减小,在基础边缘处又有所增大,基底反力分布曲线近似呈“M”形。相同荷载作用下,随着基础跨高比的增大、岩石的弹性模量增大,基底反力向基础中心集中而变更加的不均匀。(3)分析有限元软件计算结果,可以得出柱下独立基础在轴向荷载作用下首先在基础底部中心出现裂缝,随着荷载的增大基础裂缝沿着对称轴向基础边缘和基础顶部发展,最终形成贯通的裂缝。当岩石地基刚度增大、基础跨高比减小,基础首次出现裂缝时的荷载有所增大。(4)分析有限元计算结果可以发现在一定范围内随着配筋的增大对钢筋附近混凝土的应变有一定的约束作用,但对基础截面剪力和基础极限荷载几乎没有什么影响。混凝土强度等级及配筋保持不变的前提下,岩基的弹性模量越大、基础的跨高比越小,基础极限承载力越大。(5)有限元计算结果与塑性铰理论及规范计算结果进行对比,依据规范基底反力均匀分布假设,在保证一定安全冗余,利用有限元计算结果拟合提出了关于地基和基础刚度比、基础跨高比的基础截面抗剪验算公式。
[Abstract]:The characteristics of large stiffness, high bearing capacity and small deformation of rock foundation make the reaction and stress characteristics of the expanded foundation on the rock foundation different from that of the soil foundation. There are some unreasonableness in the design of independent foundation on rock foundation according to current codes. In this paper, the effects of elastic modulus of rock foundation, ratio of span to height of foundation and reinforcement on shear force of foundation section, distribution of foundation reaction force, foundation crack and ultimate bearing capacity of foundation are studied by using finite element software. The main work and results are as follows: (1) the shear force of different cross-section of foundation is calculated by using finite element software, and it is found that the shear value of cross-section of foundation approximately increases linearly in the range from the center of foundation to the edge of column. However, the shear force of foundation section decreases nonlinear from the edge of column to the edge of foundation, and the speed of the decrease changes from fast to slow and then to flat. The maximum shear force appears at the cross section between column and foundation. Under the same load, with the increase of elastic modulus of rock, the ratio of span to height of foundation decreases. The maximum shear force of foundation section is reduced. (2) the results of foundation reaction obtained by finite element analysis show that the distribution of reaction force of independent foundation under column on rock foundation is highly nonlinear. The general trend of the base reaction distribution decreases from the center of the base to the two sides of the foundation, and then increases at the edge of the foundation. The distribution curve of the base reaction force is approximately "M" shape. Under the same load, with the increase of the ratio of span to height of foundation, the elastic modulus of rock increases, and the reaction force of the basement concentrates to the center of the foundation and becomes more uneven. (3) the calculation results of finite element software are analyzed. It can be concluded that under the axial load, cracks appear in the center of the foundation base first, and along the edge of the foundation and the top of the foundation with the increase of the load, the through cracks are finally formed. When the stiffness of the rock foundation increases, the ratio of span to height of the foundation decreases, (4) the results of finite element analysis show that the strain of concrete near reinforcement is restrained with the increase of reinforcement in a certain range. However, there is little effect on the shear force and ultimate load of foundation section. On the premise that the strength grade and reinforcement of concrete remain unchanged, the greater the elastic modulus of rock foundation, the smaller the ratio of span to height of foundation, and the greater the ultimate bearing capacity of foundation. (5) the finite element calculation results are compared with the results of plastic hinge theory and code calculation. According to the assumption of uniform distribution of reaction force on the basis of the code, and in order to ensure certain safety and redundancy, a formula for calculating the shear resistance of foundation section is put forward by fitting the results of finite element calculation on the ratio of stiffness to stiffness of foundation and the ratio of span to height of foundation.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TU470
本文编号：2296073
[Abstract]:The characteristics of large stiffness, high bearing capacity and small deformation of rock foundation make the reaction and stress characteristics of the expanded foundation on the rock foundation different from that of the soil foundation. There are some unreasonableness in the design of independent foundation on rock foundation according to current codes. In this paper, the effects of elastic modulus of rock foundation, ratio of span to height of foundation and reinforcement on shear force of foundation section, distribution of foundation reaction force, foundation crack and ultimate bearing capacity of foundation are studied by using finite element software. The main work and results are as follows: (1) the shear force of different cross-section of foundation is calculated by using finite element software, and it is found that the shear value of cross-section of foundation approximately increases linearly in the range from the center of foundation to the edge of column. However, the shear force of foundation section decreases nonlinear from the edge of column to the edge of foundation, and the speed of the decrease changes from fast to slow and then to flat. The maximum shear force appears at the cross section between column and foundation. Under the same load, with the increase of elastic modulus of rock, the ratio of span to height of foundation decreases. The maximum shear force of foundation section is reduced. (2) the results of foundation reaction obtained by finite element analysis show that the distribution of reaction force of independent foundation under column on rock foundation is highly nonlinear. The general trend of the base reaction distribution decreases from the center of the base to the two sides of the foundation, and then increases at the edge of the foundation. The distribution curve of the base reaction force is approximately "M" shape. Under the same load, with the increase of the ratio of span to height of foundation, the elastic modulus of rock increases, and the reaction force of the basement concentrates to the center of the foundation and becomes more uneven. (3) the calculation results of finite element software are analyzed. It can be concluded that under the axial load, cracks appear in the center of the foundation base first, and along the edge of the foundation and the top of the foundation with the increase of the load, the through cracks are finally formed. When the stiffness of the rock foundation increases, the ratio of span to height of the foundation decreases, (4) the results of finite element analysis show that the strain of concrete near reinforcement is restrained with the increase of reinforcement in a certain range. However, there is little effect on the shear force and ultimate load of foundation section. On the premise that the strength grade and reinforcement of concrete remain unchanged, the greater the elastic modulus of rock foundation, the smaller the ratio of span to height of foundation, and the greater the ultimate bearing capacity of foundation. (5) the finite element calculation results are compared with the results of plastic hinge theory and code calculation. According to the assumption of uniform distribution of reaction force on the basis of the code, and in order to ensure certain safety and redundancy, a formula for calculating the shear resistance of foundation section is put forward by fitting the results of finite element calculation on the ratio of stiffness to stiffness of foundation and the ratio of span to height of foundation.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TU470
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