用反演分析方法进行混凝土断裂软化曲线的确定
发布时间：2018-11-23 12:49
【摘要】：混凝土作为一种建筑材料,已被广泛应用了一百多年。关于其断裂与破坏的研究一直是热点。混凝土软化本构曲线描述了断裂过程区的特性,是很多混凝土断裂模型的基础,尤其是在有限元程序模拟混凝土非线性性能的时候,软化曲线与混凝土抗拉强度以及断裂能是必要的输入参数,因此准确且方便的得出软化曲线,对混凝土断裂的研究是十分重要的。本文根据某混凝土试件基本力学试验及断裂能试验的相关资料,即混凝土三点弯曲梁试验所测得的荷载一裂缝口张开位移(P-CMOD)曲线,建立一种全自动化的确定混凝土软化曲线的反演求解过程。该方法的主要流程如下:首先假定混凝土软化曲线是双线性,创新性的将建模、拟合以及优化结合,使模拟的P-CMOP曲线与三点弯曲梁断裂试验测得的P-CMOD试验曲线高度拟合来确定相应的断裂参数。其优势在于方便、精确的对软化曲线进行求解。通过分析用反演法求解得出的混凝土双线型软化曲线得出以下结论:(1)用反演法得到的不同尺寸的混凝土三点弯曲梁试件的断裂能各不相同。说明即使同级配、同批次浇筑的混凝土试件,由于混凝土骨料分布的随机性,以及混凝土材料本身的非均质性,都会使得反演得出的不同尺寸混凝土试件的断裂能完全不同,且在一定的范围内波动。(2)双线性软化曲线的形状与试件尺寸有关,其中转折点处的纵坐标随试件尺寸的增大而增大,而转折点处的横坐标随试件尺寸的增大而减小。(3)数值模拟时,网格划分的疏密程度影响着反演计算过程的快慢;罚刚度Knn的取值影响着P-CMOD曲线荷载峰值及曲线的光滑程度。(4)w_1值影响P-CMOD曲线峰值的大小,σ1/f1与wc值共同影响P-CMOD曲线后半段的高低。本文采用在昆明理工大学水工楼现场完成的一组三点弯曲梁试验测得的P-CMOD曲线,根据文中提出的反演分析法求得该混凝土试件的双线性软化曲线,从而证明该方法具有通用性。本文将理论知识用于分析解决工程中的实际问题,对工程建设具有重要的指导意义。
[Abstract]:As a kind of building material, concrete has been widely used for more than 100 years. The research on fracture and failure has always been a hot topic. The softening constitutive curve of concrete describes the characteristics of fracture process zone, which is the basis of many concrete fracture models, especially when the finite element program is used to simulate the nonlinear behavior of concrete. Softening curve, tensile strength and fracture energy of concrete are necessary input parameters, so it is very important to get the softening curve accurately and conveniently, and it is very important to study the fracture of concrete. Based on the basic mechanical test and fracture energy test of a concrete specimen, the load-crack opening displacement (P-CMOD) curve obtained from the three-point bending beam test of concrete is described in this paper. A fully automatic inversion process for determining the softening curve of concrete is established. The main flow of this method is as follows: firstly, assuming that the softening curve of concrete is bilinear, the innovative combination of modeling, fitting and optimization, The height of the simulated P-CMOP curve and the P-CMOD test curve obtained by the three-point bending beam fracture test were fitted to determine the corresponding fracture parameters. Its advantage is that it is convenient and accurate to solve the softening curve. By analyzing the double line softening curves of concrete obtained by inverse method, the following conclusions are drawn: (1) the fracture energy of concrete specimens with different sizes obtained by inversion method for three-point bending beams is different. It shows that even with the same gradation, the same batch of concrete specimens, because of the randomness of concrete aggregate distribution and the heterogeneity of concrete material itself, the fracture energy of concrete specimens of different sizes obtained by inversion will be completely different. (2) the shape of bilinear softening curve is related to the size of the specimen, in which the vertical coordinate at the turning point increases with the increase of the specimen size. The horizontal coordinates at the turning point decrease with the increase of specimen size. (3) in numerical simulation, the density of mesh division affects the speed of inversion calculation. The value of penalty stiffness Knn affects the peak load of P-CMOD curve and the smoothness of P-CMOD curve. (4) the value of W / S affects the magnitude of peak value of P-CMOD curve, 蟽 1/f1 and wc value affect the level of the latter half of P-CMOD curve. In this paper, the bilinear softening curve of the concrete specimen is obtained by using the P-CMOD curve measured by a set of three-point bending beam tests completed in the hydraulic building of Kunming University of Technology, and the inversion analysis method proposed in this paper is used to obtain the bilinear softening curve of the concrete specimen. It is proved that the method is universal. In this paper, theoretical knowledge is used to analyze and solve practical problems in engineering, which is of great significance to engineering construction.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV431
本文编号：2351678
[Abstract]:As a kind of building material, concrete has been widely used for more than 100 years. The research on fracture and failure has always been a hot topic. The softening constitutive curve of concrete describes the characteristics of fracture process zone, which is the basis of many concrete fracture models, especially when the finite element program is used to simulate the nonlinear behavior of concrete. Softening curve, tensile strength and fracture energy of concrete are necessary input parameters, so it is very important to get the softening curve accurately and conveniently, and it is very important to study the fracture of concrete. Based on the basic mechanical test and fracture energy test of a concrete specimen, the load-crack opening displacement (P-CMOD) curve obtained from the three-point bending beam test of concrete is described in this paper. A fully automatic inversion process for determining the softening curve of concrete is established. The main flow of this method is as follows: firstly, assuming that the softening curve of concrete is bilinear, the innovative combination of modeling, fitting and optimization, The height of the simulated P-CMOP curve and the P-CMOD test curve obtained by the three-point bending beam fracture test were fitted to determine the corresponding fracture parameters. Its advantage is that it is convenient and accurate to solve the softening curve. By analyzing the double line softening curves of concrete obtained by inverse method, the following conclusions are drawn: (1) the fracture energy of concrete specimens with different sizes obtained by inversion method for three-point bending beams is different. It shows that even with the same gradation, the same batch of concrete specimens, because of the randomness of concrete aggregate distribution and the heterogeneity of concrete material itself, the fracture energy of concrete specimens of different sizes obtained by inversion will be completely different. (2) the shape of bilinear softening curve is related to the size of the specimen, in which the vertical coordinate at the turning point increases with the increase of the specimen size. The horizontal coordinates at the turning point decrease with the increase of specimen size. (3) in numerical simulation, the density of mesh division affects the speed of inversion calculation. The value of penalty stiffness Knn affects the peak load of P-CMOD curve and the smoothness of P-CMOD curve. (4) the value of W / S affects the magnitude of peak value of P-CMOD curve, 蟽 1/f1 and wc value affect the level of the latter half of P-CMOD curve. In this paper, the bilinear softening curve of the concrete specimen is obtained by using the P-CMOD curve measured by a set of three-point bending beam tests completed in the hydraulic building of Kunming University of Technology, and the inversion analysis method proposed in this paper is used to obtain the bilinear softening curve of the concrete specimen. It is proved that the method is universal. In this paper, theoretical knowledge is used to analyze and solve practical problems in engineering, which is of great significance to engineering construction.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV431
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