Experimental evaluation of the confinement of crossties on development length of 90 degree bent hooks in tension

Document Type : Original Research

Authors
M. Fatemi Ghomi 1
M. Alirezaei 2
M. Sharifi 3
S. Zareian 4
1 Department of Civil Engineering, Faculty of Engineering, University of Shahahb Danesh
2 Assistant Professor, Department of Civil Engineering, Faculty of Engineering, Islamic Azad University of Malayer
3 Department of Civil Engineering, Faculty of Engineering, University of Qom
4 Department of Civil Engineering, Faculty of Engineering, University of Shahab Danesh
10.22034/25.4.5
Abstract
Bars with standard hooks in tension are often used to anchor reinforcing bars where concrete dimensions element are not sufficient to provide the required development length for straight reinforcement. In previous researches, concrete breakout failure was the predominant failure mode of hooked bars. Closely-spaced hooks provide a lower strength per hooked bar than more widely-spaced hooked bars because the area of the breakout surface is reduced for the more closely-spaced bars. The effects of fy of bars, spacing, and confinement by ties or stirrups have been updated to reflect test results, in 25.4.3.1 of ACI 318-19. In this formula, The confining reinforcement factor ψr is based on test results reported by Ajaam et al. (2018). Base on ACI 318-19 definition, Ath is total cross-sectional area of ties or stirrups confining hooked bars. Therefore crossties are not included in the relationship. The purpose of this study is to expand the understanding of the behavior of confinement effect of crossties on development length bars with 90 degree bent hooks in tension. In this study, 3 simulated beam-column joints were tested as a continuation of previous work by Ajaam et al. (2018). The results of this experimental study show that the ACI318-19 provisions underestimate the contribution of confinement by crossties on the development length bars with 90 degree bent hooks in tension.

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[1] Iranian National Building Code, Subject #9 (2021). [In Persian]
[2] ACI Committee. (2019). Building code requirements for structural concrete (ACI 318-19) and commentary. American Concrete Institute.
[3] Ajaam, A. H., Yasso, S., Darwin, D., O’Reilly, M., & Sperry, J. (2018). Anchorage strength of closely spaced hooked bars. American Concrete Institute. doi: 10.14359/51702065
[4] Ajaam, A. H., Darwin, D., & O’Reilly, M. (2017). Anchorage strength of reinforcing bars with standard hooks. University of Kansas Center for Research, Inc.
[5] Farshadfar, O., Ajaam, A. H., Hano, M., O’Reilly, M., & Darwin, D. (2014). Bond Strength of Reinforcing Bars with Deformation Spacings that Exceed Maximum Specified in ASTM A615. University of Kansas Center for Research, Inc.
[6] Sperry, J., Yasso, S., Searle, N., DeRubeis, M., Darwin, D., O’Reilly, M., ... & Ajaam, A. H. (2017, January). Conventional and high-strength hooked bars—Part 1: Anchorage tests. American Concrete Institute. doi: 10.14359/51689456
[7] Sperry, J., Darwin, D., O’Reilly, M., Lequesne, R. D., Yasso, S., Feldman, L., & Lepage, A. (2017, January). Conventional and High-Strength Hooked Bars—Part 2: Data Analysis. American Concrete Institute. doi: 10.14359/51689457
[8] Sperry, J., Darwin, D., O’Reilly, M., Lequesne, R. D., Yasso, S., Feldman, L., & Lepage, A. (2017, January). Conventional and High-Strength Hooked Bars—Part 2: Data Analysis. American Concrete Institute. doi: 10.14359/51689457
[9] Sperry, J., Darwin, D., O'reilly, M., Lepage, A., Lequesne, R. D., Matamoros, A., ... & Ajaam, A. (2018). Conventional and high-strength steel hooked bars: Detailing effects. ACI Structural Journal, 115(1), 247-48. doi: 10.14359/51700920
[10] Peckover, J., & Darwin, D. (2013). Anchorage of High-Strength Reinforcing Bars with Standard Hooks: Initial Tests. University of Kansas Center for Research, Inc.
Modares Civil Engineering journal
Volume 25, Issue 4 - Serial Number 84
September and October 2025
Pages 49-58