A 3D mesoscopic frictional cohesive zone model for the steel-concrete interface

It is essential to model the behavior of the interfaces between steel reinforcement and concrete in order to understand the stress transfer between these two components in reinforced concrete structures, which strongly affects the initiation and propagation of cracks. The macroscopic interface models commonly used in structure simulations are functions of various parameters whose physical significance is sometimes not very clear and identification is difficult. That is why the mesoscopic scale is investigated here to improve the understanding of the behavior of the interface when considering both ribbed and smooth bars. A 3D interface model is proposed and implemented to this aim. It takes into account friction and damage by combining a modified cohesive zone model (CZM) based on Tvergaard's approach, and a frictional model in the damaged part of the interface. In this contribution, three dimensional numerical reinforced concrete samples, representing pullout tests, are generated with a detailed geometry of the steel bar. Then, pull-out numerical simulations are performed on the generated samples using an isotropic damage approach with regularization in tension and in compression in order to describe cracking in concrete. The interface model is described and its functionality is verified on a pullout test with smooth bar. The overall response is studied in terms of damage and distribution of the principle stresses near the steel bar, and the applied force versus free end displacements curves which are compared to available experimental data. Finally, a good agreement between simulations and experimental results when using smooth and ribbed bars is obtained.