Bond Performance of Reinforcing Bars in SFRC: Experiments and Meso-Mechanical Model

The bond performance of reinforcing bars in steel fiber-reinforced concrete (SFRC) remains a topic of discussion in the community. The effect of deformed steel fiber types is not fully understood, and a rational mechanics-based model is required to consider this behavior. This study experimentally investigated the bond performance of steel rebars in SFRC containing milled-cut (M) fibers with proven high bridging capacity, namely MCSFRC. The results indicated that M fibers yielded a higher bond strength of rebars compared to hook-end (H), crimped (C), and straight (S) fibers from previous studies. This was attributed to the superior bond resistance of M fibers in the matrix, provided by the rough inner surface, stiff end hook, and longitudinal twist. A meso-mechanical model (rib and fiber scale) was then developed to effectively assess the bond strength of rebars in SFRC, accounting for rib-concrete interaction, as well as the fiber reinforcement differences including fiber–matrix interaction, fiber spatial distribution, content, and dimension. This model was applicable to rebars in SFRC with H, C, S, and M fibers, and the results showed good agreement with 301 tests in the established database. On that basis, a unified local bond-slip model for rebars in SFRC was proposed, which was able to suitably reproduce the entire bond-slip response under pull-out and splitting failures.