Craft––a plastic-damage-contact model for concrete. I. Model theory and thermodynamic considerations

A framework is described for the development of a thermodynamically consistent plastic directional-damage-contact model for concrete. This framework is used as a basis for a new model, named Craft, which uses planes of degradation that can undergo damage and separation but which can regain contact according to a contact state function. The thermodynamic validity of the resulting model is considered in detail, and is proved for certain cases and demonstrated numerically for others. The model has a fully integrated plasticity component that uses a smooth triaxial yield surface and frictional hardening–softening functions. A new type of consistency condition is introduced for simultaneously maintaining both local and global constitutive relationships as well as stress transformation relationships. The introduction of contact theory provides the model with the ability to simulate the type of delayed aggregate interlock behavior exhibited by fully open crack surfaces that subsequently undergo significant shear movement. The model has been implemented in a constitutive driver program as well as a finite element program. The model is assessed against a range of experimental data, which includes data from uniaxial tension tests with and without unloading–reloading cycles, tests in which cracks are formed and then loaded in shear, and uniaxial, biaxial and triaxial compression tests.