Effect of loading frequency and stress level on low cycle fatigue behavior of plain concrete in direct tension

Due to the difficulties of direct tensile testing on concrete, only limited and often conflicting data are available. In this paper, to investigate the effect of loading frequency on the low cycle fatigue behavior of plain concrete in direct tension, several series of cyclic tension tests at different frequencies and stress levels were carried out. Especially the behavior before the initiation of macroscopic fatigue cracks in concrete, such as irreversible strain accumulation and damage evolution with the number of fatigue cycles through experiments. Test results show that the fatigue life increases with the increasing of the applied loading frequency, while decreases with the increasing of stress level. The stiffness degradation shows a typical three-stage process with the number of fatigue cycles. A new damage model considering the effect of the applied loading frequency and stress level is proposed based on the stiffness degradation and the secondary strain rate during low-cycle fatigue tests. Also, a fatigue model is proposed herein to characterize the deformation and damage behavior of concrete under cyclic tension. The calculated fatigue lives of concrete are compared with experimental data and show good fitting results.