A probabilistic fatigue model based on the initial distribution to consider frequency effect in plain and fiber reinforced concrete

The objective of this work is twofold. First, we aim to develop a new fatigue model valid for quasi-brittle materials like concrete, which properties have considerably larger standard deviation than metals. Having this in mind, we fit the measured strength data with a three-parameter Weibull cumulative distribution function and in turn take it as the initial distribution for an asymptotic fatigue model in concrete. Second, we endeavor to take into account the observed influence of frequency and stress ratio on the fatigue life in concrete, both plain and reinforced with fibers. The developed model is validated against fatigue tests in compression on cubic specimens for different stress ratios and loading frequencies. All the parameters have found physical meaning in the extensive experimental tests performed for two plain high strength concretes and two concretes reinforced with fibers. The secondary strain rate is found to be correlational with the number of cycles to failure. Finally, a reduced test procedure is proposed for fatigue strength characterization.