Title:
Effects of Concrete Tail Cover and Tail Kickout on Anchorage Strength of 90-Degree Hooks
Author(s):
Samir Yasso, David Darwin, and Matthew O’Reilly
Publication:
Structural Journal
Volume:
118
Issue:
6
Appears on pages(s):
227-236
Keywords:
beam-column joint; high-strength concrete; high-strength steel; hooked bars; reinforced concrete; tail cover; tail kickout
DOI:
10.14359/51732990
Date:
11/1/2021
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.
Related References:
ACI Committee 318, 2014, “Building Code Requirements for Structural Concrete (ACI 318-14) and Commentary (ACI 318R-14),” American Concrete Institute, Farmington Hills, MI, 518 pp.
ACI Committee 318, 2019, “Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary (ACI 318R-19),” American Concrete Institute, Farmington Hills, MI, 623 pp.
Joint ACI-ASCE Committtee 408, “Guide for Lap Splice and Development Length of High Relative Rib Area Reinf Bars in Tension (ACI 408.3R-09) and Commentary,” American Concrete Institute, Farmington Hills, MI, 8 pp.
Ajaam, A.; Darwin, D.; and O’Reilly, M., 2017, “Anchorage Strength of Reinforcing Bars with Standard Hooks,” SM Report No. 125, University of Kansas Center for Research, Lawrence, KS, 365 pp.
Ajaam, A.; Yasso, S.; Darwin, D.; O’Reilly, M.; and Sperry, J., 2018, “Anchorage Strength of Closely-Spaced Hooked Bars,” ACI Structural Journal, V. 115, No. 4, July-Aug., pp. 1143-1152. doi: 10.14359/51702065
ASTM A1035/A1035M-14, 2014, “Standard Specification for Deformed and Plain Low-Carbon, Chromium, Steel Bars for Concrete Reinforcement,” ASTM International, West Conshohocken, PA, 7 pp.
ASTM A615/A615M-15, 2015, “Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement,” ASTM International, West Conshohocken, PA, 8 pp.
Draper, N. R., and Smith, H., 1981, Applied Regression Analysis, second edition, Wiley, New York, 709 pp.
Jirsa, J. O., and Marques, J. L. G., 1972, “A Study of Hooked Bar Anchorages in Beam-Column Joints,” Reinforced Concrete Research Council Project 33, University of Texas at Austin Structures Research Laboratory, Austin, TX, 92 pp.
Marques, J. L. G., and Jirsa, J. O., 1975, “A Study of Hooked Bar Anchorages in Beam-Column Joints,” ACI Journal Proceedings, V. 72, No. 5, May, pp. 198-209.
Minor, J., and Jirsa, J. O., 1975, “Behavior of Bent Bar Anchorages,” ACI Journal Proceedings, V. 72, No. 4, Apr., pp. 141-149.
Peckover, J., and Darwin, D., 2013, “Anchorage of High-Strength Reinforcing Bars with Standard Hooks: Initial Tests,” SL Report No. 13-1, University of Kansas Center for Research, Lawrence, KS, 47 pp.
Sperry, J.; Al-Yasso, S.; Searle, N.; DeRubeis, M.; Darwin, D.; O’Reilly, M.; Matamoros, A.; Feldman, L.; Lepage, A.; Lequesne, R.; and Ajaam, A., 2015a, “Anchorage of High-Strength Reinforcing Bars With Standard Hooks,” SM Report No. 111, University of Kansas Center for Research, Lawrence, KS, 260 pp.
Sperry, J.; Darwin, D.; O’Reilly, M.; Lepage, A.; Lequesne, R.; Matamoros, A.; Feldman, L.; Yasso, S.; Searle, N.; DeRubeis, M.; and Ajaam, A., 2018, “Conventional and High-Strength Steel Hooked Bars: Detailing Effects,” ACI Structural Journal, V. 115, No. 1, Jan.-Feb., pp. 247-257. doi: 10.14359/51700920
Sperry, J.; Darwin, D.; O’Reilly, M.; and Lequesne, R., 2015b, “Anchorage Strength of Conventional and High-Strenth Hooked Bars in Concrete,” SM Report No. 115, University of Kansas Center for Research, Lawrence, KS, 281 pp.
Sperry, J.; Darwin, D.; O’Reilly, M.; Matamoros, A.; Feldman, L.; Lepage, A.; Lequesne, R.; and Yasso, S., 2017b, “Conventional and High-Strength Hooked Bars—Part 2: Data Analysis,” ACI Structural Journal, V. 114, No. 1, Jan.-Feb., pp. 267-276. doi: 10.14359/51689457
Sperry, J.; Yasso, S.; Searle, N.; DeRubeis, M.; Darwin, D.; O’Reilly, M.; Matamoros, A.; Feldman, L.; Lepage, A.; and Lequesne, R., 2017a, “Conventional and High-Strength Hooked Bars—Part 1: Anchorage Tests,” ACI Structural Journal, V. 114, No. 1, Jan.-Feb., pp. 255-266. doi: 10.14359/51689457
Yasso, S.; Darwin, D.; and O’Reilly, M., 2017, “Anchorage Strength of Standard Hooked Bars in Simulated Exterior Beam-Column Joints,” SM Report No. 124, University of Kansas Center for Research, Lawrence, KS, 330 pp.