INTERACTION EFFECT OF STEEL FIBER AND STIRRUP CONTENT ON THE SHEAR CAPACITY OF HIGH-STRENGTH CONCRETE TRANSFER BEAMS

Abstract

This study investigates the shear behavior and interaction mechanism of high-strength concrete (HSC) transfer beams reinforced with hooked-end steel fibers. The experimental program involved testing large-scale specimens using a four-point bending test setup to simulate the stress conditions in transfer girders. The key investigation parameters included steel fiber contents of 0, 30, and 45 kg/m³ (corresponding to volume fractions of approximately 0%, 0.38%, and 0.57%) and transverse reinforcement ratios (0.15% and 0.30%). The results indicate that steel fibers play a crucial role in the post-cracking behavior by providing a bridging effect across diagonal cracks. This mechanism enhances aggregate interlock and delays the yielding of stirrups, thereby transforming the failure mode from brittle diagonal tension to a more ductile shear-flexure failure. Quantitatively, the inclusion of steel fibers significantly improved the ultimate shear capacity. For the series with 0.15% stirrup ratio, the shear capacity increased from 270 kN (control specimen) to 330 kN (45 kg/m³ fiber content), representing an improvement of approximately 22%. Furthermore, the experimental results were compared with analytical predictions based on ACI 318-19, revealing that the code underestimates the capacity of fiber-reinforced transfer beams by a factor of 2.4 to 3.1, confirming the substantial safety reserve provided by the fiber-stirrup interaction.