Bond-Dependent Coefficient kb for New-Generation GFRP Bars
This article is a reply.
VIEW THE ORIGINAL ARTICLEPublication: Journal of Composites for Construction
Volume 27, Issue 6
Abstract
The new American Concrete Institute (ACI) design code for glass fiber–reinforced polymer (GFRP)–reinforced concrete (RC) members specifies a single value of 1.20 for the bond-dependent coefficient (kb) of all types of GFRP bars. This value was chosen based on test data from this project, as well as a compilation of data available in the literature. This paper reports on an experimental study that assessed the kb for the new generation of GFRP bars from five different manufacturers with different surface types: deformed/ribbed, helically deformed, helically grooved, double-helical wrap/sand-coated, and sand-coated. Two bar sizes (No. 5 and No. 8)—with 15.9 and 25.4 mm nominal diameters representing the typical range of GFRP-reinforcing bars used in practice as longitudinal reinforcement in concrete members subjected to bending—were selected from each of the manufacturers. Five RC beam replicates were used to increase experimental accuracy. Therefore, a total of 60 beams, including 50 beams reinforced with GFRP bars and 10 control beams reinforced with conventional steel bars for comparison purposes, were constructed and tested to failure according to a predetermined test method. Based on the analysis, the study confirms using the bond-dependent coefficient value of 1.20 as adopted in the new ACI design code for GFRP–RC members. This value is recommended for GFRP bars complying with (or exceeding) the material specification listed in the ASTM International standard specification for solid round GFRP bars for concrete reinforcement.
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Data Availability Statement
All data, models, and code generated or used during the study appear in the published article.
Acknowledgments
The research presented herein was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC. The donation of GFRP bars by Owens Corning (Concord, NC, USA), Pultrall Inc. (Thetford Mines, QC, Canada), B&B FRP Manufacturing Inc. (Toronto, ON, Canada), TUFBAR Canada Inc. (Edmonton, AB, Canada), and ASA.TEC GMBH (Langenlois, Austria) to support this investigation are greatly appreciated. The authors would like to express their special thanks to Jerome Lacroix, Pascal St-Laurent, and Steven MacEachern, technicians in the Department of Civil Engineering at the University of Sherbrooke, for their help during casting and testing of the reinforced concrete beams.
Notation
The following symbols are used in this paper:
- Af
- area of tension GFRP bar (mm2);
- Aim
- immersed cross-sectional area (mm2);
- b
- beam width (mm);
- c
- distance from the extreme compression fiber to the elastic cracked section neutral axis (mm);
- cc
- clear concrete cover (mm);
- d
- distance from the compression face of the concrete to the center of the tension FRP bars (mm);
- db
- bar diameter (mm);
- dc
- distance from the center of the tension bar to the tension face of the concrete (mm);
- dstirrup
- stirrup diameter (mm);
- Ec
- modulus of elasticity of the concrete (MPa);
- Ef
- modulus of elasticity of the GFRP reinforcement (MPa);
- Es
- modulus of elasticity of the steel bars (MPa);
- specified compressive strength of the concrete (MPa);
- ffu
- ultimate strength of the tension GFRP bars (MPa);
- ff
- GFRP bar stress (MPa);
- fy
- yield strength of the steel bars (MPa);
- h
- beam height (mm);
- Icr
- moment of inertia of the cracked transformed section (mm4);
- k
- ratio of the neutral-axis depth to the reinforcement depth;
- kb
- bond-dependent coefficient;
- M
- applied moment (kN·m);
- Mcr
- theoretical cracking moment (kN·m);
- nf
- modular ratio;
- s
- bar spacing (mm);
- wcr
- crack width on the tension face (mm);
- wside face
- crack width at the level of the reinforcement (mm);
- y
- distance from the centroid of the cracked transformed section to the centroid of the reinforcing bar;
- β
- amplification factor that accounts for the strain gradient;
- ɛfu
- ultimate strain of the GFRP bars;
- ɛy
- yield strain of steel bars; and
- ρf
- longitudinal reinforcement ratio of the tension GFRP bars.
References
ACI (American Concrete Institute). 2015. Guide for the design and construction of concrete reinforced with FRP bars. ACI 440.1R-15. Farmington Hills, MI: ACI.
ACI (American Concrete Institute). 2019. Building code requirements for structural concrete and commentary. ACI 318R-19. Farmington Hills, MI: ACI.
ACI (American Concrete Institute). 2022. Building code requirements for structural concrete reinforced with glass fiber-reinforced polymer (GFRP) bars—Code and commentary. ACI 440.11-22. Farmington Hills, MI: ACI.
ASTM. 2021. Standard test method for compressive strength of cylindrical concrete specimens. ASTM C39/C39M-21. West Conshohocken, PA: ASTM.
ASTM. 2022. Standard specification for solid round glass fiber reinforced polymer bars for concrete reinforcement. ASTM D7957/D7957M-22. West Conshohocken, PA: ASTM.
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Published In
Journal of Composites for Construction
Volume 27 • Issue 6 • December 2023
Copyright
© 2023 American Society of Civil Engineers.
History
Received: Apr 2, 2023
Accepted: Aug 23, 2023
Published online: Oct 3, 2023
Published in print: Dec 1, 2023
Discussion open until: Mar 3, 2024
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