A unified framework for concrete damage and fracture models including size effects

A unified approach is given for isotropic and anisotropic damage formulations for concrete fracture. The formulation encompasses the classical fixed and rotating smeared crack models, but also more refined approaches based on the microplane concept. Higher-order strain gradients are introduced to avoid the boundary value problem from becoming ill-posed at the onset of softening. Again, this has been accomplished in a unified setting. By analysing a geometrically identical anchor bolt of three different sizes it is shown that higher-order strain gradients also introduce a proper size effect in the model.