Concrete breakout in steel fiber-reinforced concrete: Database, evaluation, and design recommendations

Abstract

This study investigates the anchorage breakout capacity of steel fiber-reinforced concrete (SFRC) under tensile and shear loading, addressing gaps in existing knowledge through a comprehensive analysis of 765 experimental tests. The compiled database encompasses cast-in-place and post-installed anchors, varied fiber contents (0–2 %), deformed and straight fibers, edge effects, anchor groups, and a range of embedment depths (h_ef) and concrete strengths. The analysis showed an increase in the concrete breakout capacity due to the presence of steel fibers. A modification factor (ψ_fiber) is proposed to integrate fiber contributions into the Concrete Capacity Design (CCD) method, enabling capacity increase up to 1.5 times higher than plain concrete breakout. The factor is applicable to tensile/shear breakouts and edge-affected anchors but requires restraint for post-installed anchors with h_ef/diameter > 4.5 due to mixed failure modes. Anchors with h_ef or edge distance (c₁) <0.78 the fiber length show negligible fiber contribution due to anisotropic fiber distribution (wall-effect), revising previous recommendations. Notably, straight fibers enhance capacity comparably to hooked-end fibers, and anchor groups exhibit higher fiber contributions than single anchors, attributed to load redistribution. This work advances SFRC anchor design by validating fiber efficiency across diverse conditions, offering a robust predictive framework, and clarifying limitations for practical implementation.