Development of a Concrete Constitutive Model Considering Free Water Effect for Predicting Dynamic Responses of Concrete Structures

Existing research indicates that free water has a considerable influence on the dynamic mechanical properties of concrete, which is not considered in commonly used concrete models. This paper presents a high-fidelity constitutive model according to the Karagozian&Case model (K&C model) to capture the free water effect on the high dynamic properties of concrete structures. In this study, the new failure surfaces, equation of state and dynamic increase factor, which are in good agreement with experimental data, are put forward to consider the free water effect on concrete properties. On the other hand, a modified damage accumulation is introduced to better predict the soften stage of the stress-strain curve. The model is implemented into the livermore software technology corporation-dynamic nonlinear analysis (LS-DYNA) hydrocode through the user-defined materials subroutine. Numerical single element tests are first carried out to calibrate the parameters of the proposed model, where the numerical predictions are in good consistency with the test data. The perforation and penetration tests on concrete targets with different saturation are then simulated to verify the accuracy of the proposed model. Additionally, the influence of free water on the ballistic performance of concrete is investigated, and it is found that the presence of free water reduces the penetration resistance of concrete target.