Residual fracture toughness and fracture energy of concrete with different strengths after fatigue loading

To evaluate the residual fracture toughness and fracture energy of concrete with different strengths after fatigue loading, the static, fatigue, and fatigue-static tests were conducted on 264 three-point bending (TPB) beams, respectively. The test results showed that the residual fracture toughness and fracture energy decreased rapidly at first and then steadily with the increase of the fatigue crack tip opening displacement and the number of fatigue cycles. For a given fatigue load level, the decrease rate of the residual fracture toughness increased with an increase in the concrete strength, but the decrease rate of the residual fracture energy decreased with increasing concrete strength. Finally, the degradation models for the residual fracture toughness and fracture energy of concrete were presented. When the tensile strength of concrete, the number of fatigue cycles, and the fatigue crack tip opening displacement are known, the residual fracture toughness and fracture energy of concrete after fatigue loading are determined. The research results are helpful to assess the safety of concrete structures in-service after fatigue loading.