Effects of Concrete Tail Cover and Tail Kickout on Anchorage Strength of 90-Degree Hooks

Abstract

The effects of concrete tail cover and tail kickout on the anchorage strength of hooked bars were investigated. The study included 195 simulated beam-column joint specimens containing two No. 5, 8, or 11 (No. 16, 25, or 36) hooked bars. Bar stresses at anchorage failure ranged from 33,000 to 141,000 psi (228 to 972 MPa), and concrete compressive strengths ranged from 4490 to 16,180 psi (31 to 112 MPa). Tail cover ranged from 3/4 to 3-5/8 in. (19 to 92 mm) and tail kickout occurred for approximately 7% of the hooked bars used in the analysis. Hooked bars were placed inside or outside the column core with or without confining reinforcement in the joint region. Tail kickout was only observed in conjunction with other modes of failure and was not, in any case, the only mode of failure. The likelihood of tail kickout increases for hooked bars placed outside the column core, as compared to hooked bars placed inside the column core, as confining reinforcement within the joint region decreases, and as the size of the hooked bar increases. The anchorage strength of hooked bars with a 90-degree bend angle is not affected by hook tail covers as low as 3/4 in. (19 mm) or tail kickout at failure.