Post-fatigue properties of high-strength concrete subjected to coupled 3D fatigue-static loading

Abstract

Concrete structures suffer some damage yet not failed under fatigue load, and then continue to bear 3D redistributed stress. For this, the 3D fatigue loading considering various fatigue factors (e.g. confining stress, axial static stress (ASS) and force amplitude (FA), frequency, and cycle number) is first carried out, and then the 3D static loading is performed. The post-fatigue characteristics of high-strength concrete (e.g. P-wave velocity, S-wave velocity, porosity, gas permeability, triaxial compression strength, and elastic modulus) are gained. The results indicate that 3D fatigue loading weakens mechanical properties, delays wave propagation, and increases seepage paths. An obvious stress threshold is exhibited with increasing axial static stress and force amplitude, that is 80% triaxial compressive strength, where the physico-mechanical characteristics are rapidly weakened due to the energy dissipation caused by crack growth rises increasingly. Compared with 1D fatigue loading, the frequency turning point of weakening effect from decreasing to increasing is advanced under 3D fatigue loading due to the application of 3D stress exacerbates the heat accumulation and creep damage generation. Interestingly, the fatigue damage is likely to be more sensitive to axial load compared to confining stress during 3D fatigue loading. In other words, the promotion effect of axial fatigue load on damage is larger than the restriction of confining stress. Furthermore, the fatigue damage models considering various fatigue factors are proposed. Then, the empirical prediction models of this damage variable to mechanical parameters (strength and elastic modulus) and permeability are established to predict the capacity loss caused by fatigue loading in the design of concrete construction. The testing results in this context could facilitate our understanding of post-fatigue characteristics of high-strength concrete subjected to 3D fatigue loading and guide the safe design of concrete construction.