Behavior of steel fiber reinforced concrete beams without stirrups

Abstract

In this study, effects of steel fibers on the bending behavior of reinforced concrete beams of varying longitudinal reinforcement ratios and without stirrups are investigated experimentally and analytically. In the experimental work, two groups of simply supported beams of low and high longitudinal reinforcement ratio were manufactured. Each group had 0%, 0.5%, 1.0% and 1.5% steel fiber ratio in volume. Eight beams were tested under a load applied at midspan. In the group with lower longitudinal reinforcement ratio, steel fibers increased the bending capacity by almost 50%. However, since deformations were concentrated on a single crack, longitudinal reinforcement has ruptured and the beams could not displace as much compared to the one without steel fibers. In the group with higher longitudinal reinforcement ratio, steel fibers acted like stirrups and changed the brittle shear failure mode to a ductile bending failure. Although increasing the steel fiber ratio affected crack distributions, it did not cause a significant difference in the behavior. When analytically modeled using a common model that assume constant tensile stress at crack, computed bending capacities were lower than actual, although on the safe side. More precise models that relate tensile stresses to the crack width could give better estimations.