Concrete Monotonic and Fatigue Damage Model Based on Integration of Damage Evolution and Irreversibility of Loading and Unloading

Fatigue damage is a fundamental type of failure in concrete structural components under cyclic alternating loads. Concrete fatigue experiments are challenging and time-consuming, and hence, conducting numerical simulations for concrete fatigue has significant theoretical value. A constitutive model for concrete fatigue damage was proposed based on the irreversible loading and unloading principle and classical damage surface theory. Through analysis of the variable-amplitude fatigue loading process, the proposed model integrates the damage evolution law under monotonic loading to fatigue loading, using two correction parameters to reflect the S-N curve feature and the three-stage evolution feature of concrete fatigue damage. The relationship between the fatigue damage variable and the number of cycles was characterized using Taylor series approximation, and a cycle-jumping algorithm for fatigue simulation was established. This algorithm significantly improves simulation efficiency while ensuring accuracy. The model was verified by two uniaxial compression fatigue experiments, and the results indicated that this model accurately reflects the features of concrete fatigue failure.