Fatigue properties of plain concrete under triaxial compressive cyclic loading

Experiments were made on plain concrete subjected to triaxial static loading and constant- amplitude compressive fatigue loading with a constant lateral pressure in two directions. The initial confining pressure was 0, 0. 1f(c), 0. 25f(c), and 0. 4f(c), respectively, for the static test, and 0. 1f(c) and 0. 25f(c) for the fatigue test. Based on the triaxial compressive constitutive behavior of concrete, the inflexion of confining pressure evolution was chosen to be the fatigue damage criterion during the test. The rule of evolution of longitudinal maximum and minimum strains, longitudinal cyclic modulus and damage were recorded and analyzed. According to the Fardis-Chen criterion model and the concept of equivalent fatigue life and equivalent stress level, a unified S-N curve for multi-axial compressive fatigue loading was proposed. Thus, the fatigue strength factors for different fatigue loading cases can be obtained. The present investigation provides information for the fatigue design of concrete structures.