Anisotropic damage model for the multiaxial static and fatigue behaviour of plain concrete

A theoretical model is proposed for the description of the static and fatigue behaviour of plain concrete under uni- and triaxial loading. The model is based on damage mechanics: it features two second-order symmetric damage tensors, representative of surface damage induced by tensile or compressive strains, and a scalar variable representative of volumetric damage. Assuming independence of tensile and compressive damage variables also allows accounting for crack-closure effects. A thermodynamically consistent damage evolution law is proposed. Permanent strains upon unloading are related to damage through empirical equations. The model can cover cyclic loading inducing fatigue by means of a simple extension requiring only one additional parameter to be determined. A possible strategy for the identification of the model parameters from experiments is outlined. The reliability of the model is assessed through comparison with results of static and cyclic tests.