Experimental Research On Stochastic Damage Constitutive Law For Concrete

Although concrete is currently the most widely used construction material, its properties after suffering mechanical damages have not been fully understood. That is why there is still no generally suitable constitutive model for concrete up till now. The researches on concrete constitutive law can be divided into theoretical and experimental analyses. This paper covers both of the two categories. First, the full process properties of concrete under single-axial and biaxial loading are systematically investigated through experiments. Then a theoretical stochastic damage constitutive model is established by fully understanding the inherent stochastic characteristics of concrete.This paper studies the full process curve of concrete specimens under single-axial loading in a totally new point of view. In another word, if we think the damage evolution of concrete under single-axial loading as a stochastic process, the full stress-strain curve of every specimen can be considered as a sample of this process. Then using relevant stochastic statistics methods, the mean value, deviation and variance curves of this process can be obtained, which provides the basis for further analyzing the nonlinear and stochastic properties of concrete under single-axial loading.The full stress-strain curves of concrete specimens under biaxial proportional loading are obtained after analyzing the experimental data. And the curves are further investigated considering different boundary conditions. Finally the strength envelope of concrete in stress and strain spaces is established by extracting the strength parameter from the full curves, and the variation range of the envelope is discussed.Based on previous researches of our group and the phenomena and results of this experiment, this paper discusses the micro-damage mechanisms of concrete and indicates that there are two essential damage mechanisms, i.e. tensile damage and shear damage. Then two stochastic damage constitutive models are developed for corresponding mechanisms, respectively. Furthermore the axial compressive damage is described by the modified shear damage model. The numerical simulations by these models agree well with experimental data.