Study On Damage And Fracture Behavior Of Concrete Based On Macro And Meso Mechanics

Based on numerical simulation incorporating with experimental tests, the mechanical behaviors of concrete are studied from meso-scale to macro-scale, considereing the deformation, damage and nonlinear fracture behavior. Thus, a meso-damage model for studying the fracture behavior of concrete is presented; meanwhile, a multiscale method for bridging the relationship between mesoscopic and macroscopic level are presented, laying a foundation for further study of damge and fracture mechanism of heterogeneous and quasi-brittle materials. The study includes:1. An efficient approach to dispose aggregates of concrete and a state matrix method to generate mesh coordinates for random aggregates are proposed. Based on the continuum mechanics, a multi-phase mesoscale model of concrete with nonlinear damaged stress-strain constitutive relations to describe mechanical behaviors of concrete is presented. With the numerical model, the complete process of concrete with mode I and mode I-II types of fracture are analyzed by numerical simulation.2. Based on the multi-phase meso-mechanics model, a simulation analysis of mechanical properties of rock-fill concrete is accomplished. Herein, experimental tests for determining basic mechanical parameters of three components, i.e. rocks, self-compacting concrete and interfaces are conducted, and four-point flexural beam tests for verification reliability of the model are designed. It is preliminarily shown that the numerical model is reliable.3. By introducing the Weibull probabilistic distribution for heterogeneities of mechanical properties of multi-phase concrete components and damage localization, influence of heterogeneity of the components on the concrete strength is analyzed. An improved model is also presented by introducing spatial correlation length factor into the Weibull distribution law. Effects of spatial correlation length on the concrete strength are studied.4. Based on the multiscale homogenization theory and finite element method, the meso-macro equivalent elastic constitutive relationship of concrete is established. Herein, the influence of unit cell size on the elastic properties in macro-scale is studied, and the minimum ratio of unit cell size to the maximum aggregate diameter has been obtained. Comparisons between the macroscopic and the corresponding mesoscopic simulations of a 3-Point concrete beam are accomplished.5. A series of uniaxial compression tests for different size cube self-compacting concrete specimen are carried out, and size effect of concrete strength, end effects on concrete strength and failure pattern are studied, comparing with corresponding numerical simulations based on the concrete equivalent probabilistic model. It is concluded that the numerical model can provide reasonable results in the analysis of size effect for concrete.6. As an engineering application, the fracture and damage behavior of Koyna gravity dam during the 1967 earthquake is analyzed by the equivalent probabilistic model of the concrete, the cracking pattern and failure modes of the dam prototype during the event are justified.