Side-Face Blowout Strength of 43 and 57 mm (No. 14 and No. 18) Hooked Bars in Beam-Column Joints

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Title: Side-Face Blowout Strength of 43 and 57 mm (No. 14 and No. 18) Hooked Bars in Beam-Column Joints

Author(s): Sungchul Chun, Min-Seo Bae, and Byung-Soo Lee

Publication: Structural Journal

Volume: 114

Issue: 05

Appears on pages(s): 1227-1236

Keywords: exterior beam-column joint; hooked bar; reinforcement; sideface blowout

Date: 9/1/2017

Abstract:
The confining effects of the cover and transverse reinforcement are excluded from the ACI 318 provisions on the development length of 43 and 57 mm (No. 14 and No. 18) hooked bars because of the absence of experimental evidence. Twenty-six simulated beamcolumn joint tests were therefore conducted using 43 and 57 mm (No. 14 and No. 18) hooked bars of 550 MPa (80,000 psi) yield strength in this study. The test variables include the embedment length, concrete compressive strength, side cover, and transverse reinforcement. An intentional side-face blowout failure occurred due to the prevention of the other failure modes. As the embedment length and side cover increased, the anchorage capacity of the hooked bars increased as well. By placing ties, the anchorage strength of the hooked bars increased, but a wide scattering of the improved strengths also occurred. At failure, the entire bar force was resisted by the hook bearing only, and the bond along the straight region of the hooked bars vanished. From regression analyses of 74 datasets, including Marques and Jirsa’s tests, a model is proposed for predicting the anchorage strength of hooked bars terminated within exterior beam-column joints.