Theoretical model for mode I fatigue crack growth of concrete under different loading frequencies

Abstract

Loading frequency is a critical factor that influences the mode I fatigue fracture of concrete. However, it is neglected in existing theoretical models, which limits their applicability. To address this issue, a new model for mode I fatigue fracture of concrete is developed in this study. This model converts the loading frequency into the loading rate, and introduces the rate-dependent crack growth criterion and cohesive constitutive model. The predicted fatigue crack growth process of three-point bending (TPB) beams under varying loading frequencies agrees well with the experimental results, thereby verifying the model’s effectiveness. Subsequently, based on the model, a quantitative analysis of fatigue life and crack growth of concrete under varying loading frequencies is conducted. The results indicate that the initial cracking load of TPB beams increases with increased loading frequency. When the load exceeds the fatigue peak load, specimens show infinite fatigue life. The ultimate load of TPB beams under monotonic loading increases with improved loading frequency. The fatigue crack growth of concrete is frequency-independent when the rate-dependent ultimate load is used to determine the fatigue load. The investigation provides a practical approach to quantify the frequency-dependent growth of fatigue cracks. Meanwhile, it reveals the mechanisms behind increased fatigue life and decreased fatigue crack growth at higher frequencies. Namely, the rate effect of concrete improves both the initial cracking load and ultimate load. It contributes to a reasonable evaluation of the stability of fatigue cracks and an in-depth understanding of the fatigue fracture of concrete under different loading frequencies.