Hooking Effect on Flexural Strength and Toughness of Steel Fiber-Reinforced Concrete Beams

Abstract

End hooks of steel fibers provide a stronger bridging force across the concrete matrix in steel fiber-reinforced concrete (SFRC). In this work, SFRC beams were prepared with steel fibers of the same length and diameter but different types of end hooks (straight, three-dimensional [3D], four-dimensional [4D], and five-dimensional [5D]) at increasing fiber volumes (0.0, 0.5, 1.0, 1.5, and 2.0%). Four-point bending tests conducted on each SFRC beam yielded load-deflection curves, from which the first cracking strength, flexural strength, and fracture toughness up to certain deflection-to-beam length ratios were obtained. The test results showed that the presence of end hooks remarkably enhanced the flexural strength and toughness of the SFRC beams, and this enhancement was amplified with an increasing number of hooks. Quantitative analysis revealed the hooking index, a factor introduced herein to delineate the efficiency of various types of hooks, was 1.00, 1.30, 1.60, and 2.10, respectively, for straight, 3D, 4D, and 5D steel fibers used in the present study. Lastly, empirical models for predicting flexural strength and toughness were established with high prediction accuracy.