A MICROSCOPIC APPROACH TO RATE EFFECT ON CONCRETE STRENGTH UNDER COMBINE LOAD

摘要

The enhancement of concrete strength under combined dynamic load is investigated in this paper. As we know, concrete structures in engineering often suffer dynamic loading, so that the research on the dynamic mechanical properties of concrete has great significance. It has been shown by the current available publications that the rate effect of concrete is affected by two effects, the free water viscosity dominating under lower loading rate, and the inertia effect under higher loading rate. In this paper, a crack in an infinite solid subjected to linear loading normal to the crack surface is considered accounting for these two effects. Based on linear elastic dynamic fracture mechanics, the influence of free water viscosity is concerned by means of viscous cohesive force on the crack surface known as Stefan effect, in which the magnitude of viscous cohesive force is assumed to be in proportion to loading rate. Based on the sliding crack model, the compressive strength is obtained by considering the interaction between microcracks with Kachanov method. The reason why rate effect of concrete under compression is much smaller than under tension is presented and failure model difference between dynamic loading and static loading under compression is indicated. The relationship between the dynamic strength increase factor and the strain rate both under tension and under compression is obtained. With the help of the analysis of rate effect of concrete under linear increasing load, different kinds of load functions and load combination is considered. A comparison between the theoretical result and the experimental data published in the literature has been made and shown that a good agreement is achieved.