Fatigue behavior and prediction model of self-compacting concrete under constant amplitude load and incremental amplitude load

To explore the fatigue fracture behavior of self-compacting concrete (SCC), constant amplitude loading tests and incremental amplitude loading tests were carried out. The experimental results of SCC were obtained and analyzed, including P-CMOD curve, fatigue life, effective crack length, fatigue crack growth (FCG) rate, stress intensity factor (SIF). The results show that the P-CMOD curves of SCC beams follow the unique envelope theory. The fatigue damage of SCC under constant amplitude load can be divided into three stages. In the second stage, cracks grow steadily. The critical SIF is the boundary point between the second and the third stages of fatigue damage. When SIF exceeds the critical SIF, cracks develop rapidly. The first stage of fatigue damage is not obvious for incremental amplitude loading tests. With the increase of load amplitude, there are obvious second and third stages of damage. Except for the maximum load stage, the crack opening rate keeps constant generally. Combined with damage mechanics and fracture mechanics, damage evolution equations of SCC under constant amplitude load and incremental amplitude load were established. The parameters of fatigue damage model based on continuous damage mechanics (CDM) were calibrated by test data, and the predicted results were compared with the experimental results. The results show that the model is sensitive to the first stage of damage. The fatigue damage model based on CDM is more suitable to predict fatigue life for incremental amplitude tests and constant amplitude tests with high cycle. The advantage of this model is that it can be applied to predict fatigue life for different load levels.