The Experimental Investigation On The Mechanical Behaviors Of Concrete Under Complex Loading Paths

Nowadays, the concrete material is one of the most widely used constructing materials in project constructing. It is widely applied to some large complicated structure, such as large-scaled dam, ocean plat, tidal power plant and so on. Also, the study for mechanical behaviors of concrete is one of the studied hotspots for mechanical investigator. The dissertation carefully deals with the mechanical behaviors of concrete under uniaxial and triaxial cyclic loading. After the analysis of elastoplastic damage constitutive model based on non-classical plastic theory, the corresponding numerical algorithm is developed to simulate the response and damage of concrete subjected to complex loading histories.The MTS815 hydraulic servo system, which can provide 2800kN of longitudinal load, 80MPa of confined pressure, is used in the experiment. The specimens were tested on the MTS815 hydraulic servo system for the uniaxial cyclic compressive experiments to study the effect of concrete mechanical behaviors under the three factors of cyclic frequency, cyclic increment and initial load. It is found that, the factors have little effects on the peak strain in this experiment. Among them, cyclic frequency and cyclic increment have a little effect on the uniaxial cyclic compressive strength; the initial load has certain effect on the strength.The triaxial compressive experiments include triaxial equal confined pressure monotonic experiment and cyclic loading experiment. The effect of confined pressure to the concrete mechanical behaviors is considered. It is found that, the confined pressure has some effects on the two kinds of loading conditions. As the confined pressure enhances, the strength increases, and at the same level of confined pressure, the strength of triaxial monotonic and cyclic loading are approaching. But in the case of strain, as the confined pressure enhance, the strain of triaxial monotonic loading are lager than the triaxial cyclic loading.Making use of irreversible thermodynamics with internal variables and the concept of continuum damage mechanics, a elastoplastic damage constitutive model is proposed by introducing generalized time defined in the space of irreversible strain and Newtonian time, taking into account the anisotropic nature of the micro-defects in rock and rock-like materials. The anisotropic evolution and unilateral effect of damage as well as the effect of hydrostatic pressure and can be taken into account in the developed model. The corresponding numerical analysis is established to computer the response and damage of concrete subjected to complex loading histories. It shows that the calculated results agree well with the experimental observation. The influence of confined pressure to the strength and deformation can be well described with the model.