Damage constitutive model for performance degradation of concrete due to compressive fatigue load

An anisotropic damage model for concrete subjected to compressive fatigue load is developed based on continuum damage mechanics and the concept of boundary surface. The equations of loading surface and boundary surface are expressed in strain-energy releasing rate.The damage state in various levels is described by the position at the interface among the loading surface, incipient damage surface and boundary surface in the energy releasing space. The variation law of the ultimate breaking surface is determined according to the relationship between cumulative damage and the energy releasing rate threshold. Based on the uniqueness assumption of deformation, the relationships among concrete fatigue, concrete damage due to monotonic cyclic load and stress-strain are obtained. This result helps to clarify the law of performance degradation of concrete experienced various loading history. The parameters of the model are obtained by means of monotonic compressive, single state fatigue and multi-stage fatigue combining with monotonic compressive tests. The calculation result of the model is in good agreement with experimental data.