Effect of steel fibers on the cracking behaviour of reinforced concrete elements

The incorporation of fibers in conventionally reinforced concrete beams improve the shear behavior and control the evolution of cracks and deflections with consequent positive effects on the service life of concrete structures. A cooperation research project is in progress with the aim to investigate the influence of different contents and types of fibers on the cracking behavior of reinforced concrete beams under flexure. As a first step, the influence of steel, glass or polymer macrofibres on the crack pattern, the bearing capacity and the failure type of beams with a typical value of longitudinal reinforcement ratio (0.87 %, bars of 10 mm diameter) were tested. This paper presents the first results of the second part of the research where the effect of the longitudinal reinforcement is analyzed by testing concrete beams with 0, 25 and 50 kg/m3 of steel fibers with reinforcement longitudinal ratios of 0.55 and 1.27 % (bars of 8 and 12 mm diameter respectively). Crack characteristics and deflections are evaluated as a function of fiber concrete residual toughness parameters. It is verified that fibers improve the bending behavior at serviceability limit state and ultimate limit state of conventional reinforced concrete.