Influence of steel fibers on the flexural behavior of RC beams with low reinforcing ratios: Analytical and experimental investigation

In this work, the results of an experimental program intending to investigate the flexural characteristics of reinforced steel-fiber concrete beams (S/SFRC) are reported and discussed. Hooked end steel fibers with aspect ratios of 45 or 80 were used to produce matrices with fiber content ranging from 0 to 2%, in volume, and high compressive strength. A full mechanical characterization was carried, including the post-peak properties for concrete matrix in tension. Beams with reinforcing ratios of 0.28, 0.44 and 0.70% were analyzed using digital image correlation (DIC) to monitor displacement field and cracking distribution throughout the constant moment region during loading. Data reported included load-deflection and moment-curvature curves, evolution of compressive strains in concrete and neutral axis depth, spacing and openings of cracks and failure modes. Tests revealed gains of capacity ranging from 21 to 109% of R/SFRC with respect to plain RC beams and significant reductions in crack openings for a given rebar stress. R/SFRC beams exhibited sufficient plastic rotation capacity, but with a reduction in plastic hinge length as a consequence of the phenomenon of crack localization. Comparisons with current code provisions show that these are adequate for the design but residual stresses obtained from direct tensile tests are more appropriate.