Effect of steel fibers on the shear behavior of high strength concrete beams

Shear failure of reinforced concrete beams is generally affected by a large number of parameters among which the a/d ratio (shear-span/effective depth) is the most important. The other main parameters are the compressive strength, the longitudinal reinforcement ratio, the aggregate and the presence of transverse stirrups. The addition of steel fibers as reinforcement could be another parameter which contributes to the shear resistance. Such shear contribution will be assessed qualitatively and quantitatively for high strength concrete in the present work. Twenty four steel fiber reinforced high strength concrete beams without stirrups and with stirrups were tested in bending under two concentrated loads; the concrete beams were designed to have a pronounced shear behavior. The possibility of replacing traditional transverse reinforcement by steel fibers was studied. In this sense, the main testing parameters were the volume fraction of steel fibers, the aspect ratio of fibers and the presence of stirrups; five volume fractions of fibers were used (0%; 0.5%; 1.0%; 2.0% and 3.0%), with two aspect ratios (l(f)/d(f) of 65 and 80). The experimental results show that the shear behavior of the fiber reinforced high strength concrete beams without stirrups is similar, if not better, to that of high strength concrete beams containing stirrups reinforcement. The fiber reinforced beams had very narrow diagonal cracks and improved shear strengths, particularly for fiber fractions from 1% to 3%. Based on the present experimental work, a new empirical model is proposed for the contribution of the fibers to the shear strength of high strength concrete beams. The proposed model was assessed against other existing models and against varied experimental data taken from the literature and found relatively more satisfactory. (C) 2015 Elsevier Ltd. All rights reserved.