Shear Behavior of Deep Beams Reinforced with Single- and Dual-Geometry Steel Fibers

This experimental study investigated the shear capacity, load–deflection behavior, and failure modes of steel fiber reinforced concrete (SFRC) deep beams incorporating single-type and dual-geometry steel fibers. Eleven SFRC deep beams, with and without traditional shear reinforcement, were tested under four-point loading to examine the effect of steel fiber (SF) content, shape, and combination on shear performance. SF volume fractions of 0.0%, 0.7%, 1.05%, and 1.4% (by cement weight) were evaluated across three fiber configurations: hooked-end fibers, crimped fibers, and a 50/50 dual-geometry combination of both. Conventional shear reinforcement was also tested to serve as a benchmark. Results showed that shear strength and ductility increased consistently with fiber content, with load-carrying capacity reaching 165–211% of the unreinforced control beam and 111–140% of the beam with conventional shear reinforcement. Failure has been shifted from a sudden, brittle diagonal-shear mode in the unreinforced beam toward more gradual, ductile failure as fiber content increased, accompanied by finer crack widths and more distributed cracking. While both single-type fibers performed effectively as standalone shear reinforcement, the dual-geometry combination of hooked-end and crimped fibers outperformed either single type in ultimate strength and ductility, indicating a synergistic effect between fiber geometries. This dual-geometry approach offers a novel strategy for optimizing fiber-reinforced shear design in deep beams, particularly where enhanced ductility and crack control are needed without relying solely on conventional shear reinforcement.