Postpeak Behavior of Fiber-Reinforced Concrete under Cyclic Tensile Loads

High-strength concrete (HSC) and fiber-reinforced concrete (FRC) are being increasingly used in bridges, pavements, off-shore platforms, and water-retaining structures. These structures are subjected to fatigue loadings caused by vehicles, waves, machine rotations, or even earthquakes. In this study, the role of steel and carbon fibers on fatigue behavior of normal strength concrete (NSC) and HSC is investigated. Experimental results from uniaxial tensile tests on cylindrical specimens and four-point bending tests on beam specimens allowed a comparison between material and structural behavior. Geometrically similar beams with different sizes were adopted. Experiments focused on precracked specimens in which a fracture process zone was present. To study the material behavior, both inner loops and cycles on the envelope curve were applied. It was found that the envelope curves obtained from cyclic tests match the curves obtained from the static tests on cylinders of HSC and FRC quite well. This, however, does not occur in beam specimens because the fatigue damage strongly depends on the fracture process zone development, which is influenced by specimen size and loading history. Furthermore, the effectiveness of steel fibers in improving fatigue life is greater in HSC than in NSC cylindrical specimens. More specifically, the presence of steel fibers in HSC resulted in a smaller crack opening increment per cycle. The number of cycles to failure depends on the beam size because of different fracture process zone development. Finally, a comparison between experimental results and an analytical model for crack increment during inner loops again demonstrated the influence of fibers on fatigue behavior of concrete.