Efficiency of Steel Fibers in Improving the Performance of Concrete Beams without Shear Reinforcement

This research aims to experimentally study the shear strength of steel fiber concrete beams without shear reinforcement (stirrups). Parameters of the study include two compressive strength (20, 50 MPa), three ratios of flexural reinforcement (0,77, 1,14, 1,54 %), two ratios of shear span to effective depth (a/d = 2,3), and two types of aggregates (Natural coarse aggregate and recycled aggregate (crushed bricks)) with and without steel fibers. Three ratios of the volume fraction of steel fiber are used in the study (0, 0,5, 1 %). All specimens were loaded to failure. Thirteen specimens of concrete beams without shear reinforcement were tested with dimensions (200 x 300 mm) for cross-section (width, depth) and length (2000 mm). The beams were examined to evaluate the effect of each of the above variables on the shear strength and behavior of the beams. All beams are designed to fail with shear stress (without shear reinforcement) under a two-point load test. After obtaining and analyzing the practical results, a set of conclusions were made clear, as the results showed that increasing the compressive strength leads to increases in the maximum shear strength by (60 %). Also, the increase in the flexural reinforcement causes increases in the maximum shear strength by (53 %). As for the ratio of shear span to effective depth, the effect is the opposite, the increasing from 2 to 3 leads to a decrease in shear strength by (30 %). As for the type of aggregate, replacing 50 % of the natural coarse aggregate with recycled aggregate (crushed bricks) leads to a decrease in the maximum shear strength by (10,5 %). The results also show the efficiency of the steel fibers by improving the behavior of the beams under loading, as the addition of steel fibers by 0,5 % increases the maximum shear strength by (18 %). Still, when the steel fibers are 1 % of the volume of concrete, the amount of improvement in shear strength ranges from (30-50 %) despite the difference in the details of the specimens