Shear Behavior of Steel Fiber-Reinforced Concrete Beams without Stirrup Reinforcement

Results from a comprehensive investigation aimed at studying the behavior of steel fiber-reinforced concrete (SFRC) beams in shear, as well as the possibility of using steel fibers as minimum shear reinforcement, are presented. A total of 28 simply supported beams with a shear span-to-effective depth ratio of approximately 3.5 were subjected to a monotonically increased, concentrated load. The target concrete compressive strength for all of the beams was 41 MPa (6000 psi). The studied parameters included beam depth (455 or 685 mm [18 or 27 in.]), fiber length (30 or 60 mm [1.2 or 2.4 in.]), fiber aspect ratio (55 or 80), fiber strength (1100 or 2300 MPa [160 or 330 ksi]), and fiber volume fraction (between 0.75 and 1.5%). In total, three types of steel fibers were considered, all with hooks at their ends. The behavior of beams failing in shear prior to or after flexural yielding was also investigated by varying the longitudinal reinforcement ratio (1.6, 2.0, and 2.7%). Test results showed that the use of hooked steel fibers in a volume fraction greater than or equal to 0.75% led to multiple diagonal cracking and a substantial increase in shear strength compared to reinforced concrete (RC) beams without stirrup reinforcement. All SFRC beams sustained a peak shear stress of at least 0.33 root f'(c) MPa (4.0 root f'(c) psi). The results also indicated that the hooked steel fibers evaluated in this investigation can safely be used as minimum shear reinforcement in RC beams constructed with normal-strength concrete and within the range of member depths considered.