Strength effect on the fatigue crack growth of concrete

Abstract

In this dissertation, the fatigue life and fatigue crack growth behaviors of concrete are investigated on the basis of damage and fracture mechanics. Modified prediction models considering the effect of concrete strength are also suggested. The range and level of concrete strength used in structural members subjected to fatigue loading have become wider and higher, respectively. The mechanical properties are influenced by concrete strength. Most design codes, however, have assumed that fatigue life is independent of concrete strength. Therefore, in order to construct a more accurate prediction model and safer design code, detailed experimental evidences of strength influence are needed. In addition, more interest has been shown in the examination and rehabilitation of structures during service life. For execution of structural inspection, it is necessary to establish the fatigue crack growth model. Although, a few works on fatigue crack growth have been carried out, there still is not enough information. In this study, cylindrical concrete specimens with various strength levels were tested to investigate the fatigue strength and life in axial compression. The experimental results indicated that the fatigue life decreases with increasing concrete strength. Based on these results, a modified fatigue life model considering the effects of concrete strength was proposed. In this model, to directly use the actual compressive strength as the reference of fatigue strength, the strain rate effect was taken into account. The verification of the proposed fatigue life model was conducted by fatigue damage, i.e. fatigue deformation, approach. It was found that the fatigue strain increment rate increases severely as the concrete strength increases. This means that fatigue life should decrease as concrete strength increases. As a result, higher-strength concrete becomes more brittle and less resistive than lower-strength concrete under fatigue loading. In most structural m...