Use of Steel Fibers as Shear Reinforcement

Investigations on the behavior of steel fiber reinforced concrete beams subjected to predominant shear are presented. The results of some 49 shear tests carried out on simply supported rectangular beams under symmetrically placed concentrated loads are presented and analyzed; of these, 10 beams contained conventional stirrups and 33 were reinforced with crimped steel fibers as web reinforcement. The parameters varied were the volume fraction {rho}f of the fibers, fiber aspect ratio L/D, concrete strength fcu, amount of longitudinal reinforcement {rho}, and the shear span/effective depth ratio a/d. The test results show that the first crack shear strength increased significantly due to the crack-arresting mechanism of the fibers; the improvements in ultimate shear strength were of the same order as that obtained from conventional stirrups even for a fiber volume fraction of 1 percent. Any further increase in fiber contents did not result in corresponding improvements in the shear strengths. Based on these tests and on tests by previous investigators, predictive equations are suggested for evaluating the cracking shear strength and ultimate shear strength of fiber reinforced concrete beams. The comparisons between computed values and the experimentally observed values are shown to validate the proposed theoretical treatment.