Anchorage of High-Strength Reinforcing Bars with Standard Hooks - Initial Tests

Abstract

The effects of embedment length, side cover, quantity of confining transverse reinforcement, location of hook (inside or outside the column core), concrete compressive strength, hooked bar size, and hook bend angle on anchorage capacity are investigated using the results of 329 tests of standard hooks loaded in tension. No. 5, 8, and 11 hooks were tested in beam-column joints with concrete compressive strengths ranging from 4,300 to 13,700 psi. The results of the tests are compared with the provisions in ACI 318-11, and equations to describe the anchorage strength of 90° hooks for hooks not confined by transverse reinforcement, hooks confined by two No. 3 ties, and hooks confined by No. 3 ties spaced at 3db are developed. Hooks cast inside the column core have greater ultimate anchorage force than those cast outside the column core, hook bend angle has a negligible effect on ultimate anchorage force, and ultimate anchorage force increases as the quantity of confining transverse reinforcement increases. For hooks not confined by transverse reinforcement, the anchorage capacity increases more rapidly than embedment length. For hooks confined by transverse reinforcement, small embedment lengths develop significant anchorage forces; increases in embedment length result in additional capacity, but anchorage capacity is less than proportional to embedment length. Comparisons to the provisions in ACI 318-11 show that the ultimate anchorage force of larger hooked bars and the effect of concrete compressive strength are overpredicted by the current design requirements. Analysis of 90° hooks cast inside the column core show that there is an increase in ultimate anchorage force with an increase in bar diameter; this effect increases as the quantity of confining transverse reinforcement increases within the range of values evaluated in this study. Ultimate anchorage force also increases with an increase in cover to the center of the bar for bars not confined by transverse reinforcement; this effect decreases as the quantity of transverse reinforcement increases and has no effect for bars confined by No. 3 ties spaced at 3db.