Anchorage Strength Model for Large-Diameter Headed Bars Anchored at the Cutoff Point

Design guidance for headed-bar development remains uncertain for large-diameter bars at cutoff points, where bar termination increases anchorage demand and confinement is often limited. This study quantified the anchorage behavior of 43 and 57 mm headed bars and established a regression-based strength model grounded in a splitting-controlled bond–bearing mechanism. Nineteen reinforced concrete beam specimens were tested under four-point loading configured to place the bending-moment inflection point at the head location. The primary variables were the development length (ldt = 12–28db), concrete compressive strength (fc′ = 42 and 70 MPa), clear side cover, clear spacing, and transverse reinforcement index (Ktr/db = 0–2.0). All the specimens failed by splitting prior to bar yielding, characterized by longitudinal cracking along the development region and cover spalling near the head. The anchorage strength increased with concrete compressive strength and development length and was most strongly enhanced by transverse reinforcement (up to ~60%). At failure, the bond contributed 70–86% of the developed stress, while the head-bearing contribution increased with confinement. Existing ACI 318-19 and KDS-2021 provisions were generally unconservative, particularly for unconfined specimens. The proposed bond–bearing model showed a close agreement with the test database (mean test/prediction = 0.99; COV = 4.72%) within stated parameter limits.