Elastoplastic nonlocal damage model for concrete and size effect analysis

This work deals with a combination of plasticity and nonlocal damage formulation for modelling concrete structure behaviour subjected to mixed mode failure. Plastic effect, driven by effective stress, is an hardening process and accounts forthe development of irreversible strains while softening is controlled by damage to describe the degradation of the material stiffness. A regularization technique, based on the implicit gradient definition of the nonlocal strain tensor, is introduced to overcome the deficiencies induced by the softening damage relation i.e., spurious strain localization and dependance of the energy dissipation on mesh refinement. A 3D tensile bar localization benchmark is used to validate the effectiveness of the regularization technique. Moreover, simulation of reinforced concrete continuous deep beam is studied to illustrate the improvements achieved by coupled law compared to scalar damage models. Finally, size effect in mixed mode failure is investigated by mean of three asymmetric four-point bending tests on notched specimens.