Influence of stress state on dynamic behaviors of concrete under true triaxial confinements

The strain rate sensitivity and stress state are two important factors affecting the mechanical behavior of concrete under dynamic load. However, few studies involved high strain rates and different stress states. Herein, the strain rate effect and intermediate principal stress effect of concrete are studied by using the true triaxial Hopkinson test system, and the influence of heterogeneity under dynamic load is also discussed. A series of experiments, including the static biaxial and static triaxial confinements, are conducted to investigate the intermediate principal stress effects by a dynamic testing system for cubic concrete specimens under static triaxial confinements. The results show that the triaxial experimental data show good consistency with the dynamic M-C strength, but the biaxial experimental data deviate greatly from the dynamic M-C strength, which indicates evident the intermediate principal stress effect. The Drucker-Prager (D-P) model is then modified to describe the intermediate principal stress dependence and loading rate effect by introducing the Lode angle (theta) and the strain rate, and better simulation results are obtained. The meso finite element model (meso-FEM) is employed to further explain the effects of non-uniformity in concrete specimens, and a Weibull-type modification is introduced to describe the transversal inertia effect due to concrete heterogeneity. Although the relative dynamic stress (eta = (sigma x - sigma e)/sigma x) in the x-axis is rate-dependent, hydrostatic pressure-dependent, and size-dependent, the relation of eta to the stress triaxiality is insensitive to these effects. This work would provide experimental and theoretical guidance for the effect of stress state on the mechanical behavior of concrete under dynamic load.