Study On Stochastic Damage Constitutive Of Higher Strength And High Performance Concrete

Concrete material is widely used in the building structures, for its characteristics of obtaining material easily and good durability. Different from the isotropic homogeneous materials (e.g. shaped steel) the concrete is a kind of composite material with properties of heterogeneity, porosity and anisotropy, which reflect as stochastic and discreteness on the macro-mechanical properties of concrete. Stochastic and discreteness will have an influence on mechanical properties and the seismic performance of concrete structure. Compared with normal concrete, strength of cement paste in ultra-high strength and high performance concrete (UHSHPC) is close to, or even greater than that of coarse aggregate.First of all, three kinds of concretes with various strength levels are made in this paper. The influence of the cement grade, cementitious materials, coarse aggregate gradation, sand ratio, superplasticizer and water-cement ratio on the mechanical properties of concrete are analyzed. Uniaxial compression tests on 15 specimens, which are divided into 3 groups, are performed to research the damage and failure mechanism of UHSHPC. The elastic modulus of concrete is measured in the process of compression periodically. The damage index is defined as the ratio of variation of elastic modulus in the process of damage to initial elastic modulus. A double parameters damage function is established to research the damage evolution rules, based on study about variation of damage index obtained from the tests. A uniform mesoscopic model made up by two springs, one slipper and one displacement constraint element is proposed, based on Yu Liu's spring-friction model and Li Jie's spring model. The stochastic damage constitutive relationships are established for normal concrete and UHSHPC under uniaxial tension, for the energy conservation principle in the damage process. A mass block is introduced to the model above to establish the dynamic damage model, which is applied to normal concrete and UHSHPC. Consequently, the dynamic stochastic damage constitutive relationship of normal concrete and UHSHPC are found. Comparison between theoretical and experimental results of ordinary concrete and UHSHPC have verified that the constitutive relationship established in this paper can describe the failure mechanism of concrete well.The results of this study provide a theoretical foundation for wider application of HSHPC, and a profound knowledge and understanding about the mechanism of each component of concrete for engineers. This study provides some references for the further study of concrete mechanical properties subjected to multiaxial stress.