Influence of Steel Fibers in Fatigue Resistance of Concrete in Direct Compression

The influence of steel fibers on the fatigue resistance of concrete in direct compression, based on experiments, and an assessment of it through neural network modeling have been presented. Both straight and hooked fibers were incorporated in the concrete. The volume fraction was 1% for straight fibers, and both 1 and 2% for hooked fibers. The applied stress levels ranged from 0.55 to 0.95 of the (static) compressive strength. The number of cycles was up to 1,000,000. The neural network was based on a feedforward back-propagation algorithm. Steel fibers enhanced the fatigue strength, distinctly, at all stress levels. Hooked fibers improved the fatigue strength more than the straight ones; the larger the fiber content, the greater was the enhancement of fatigue strength. Strains measured just before failure showed that fiber reinforced concrete could undergo larger strains before failure than plain concrete. Based on strains measured throughout the fatigue cycling, stages of dilation and failure have been apparent. The adopted neural network modeled both the S-N (strength-number of cycles) and strain-N behaviors extremely well. It was considered possible to extrapolate the S-N behavior beyond 1,000,000 cycles in order to estimate the fatigue strength in the super-high cycle ranges of 107 and more.