Postpeak Stress–Strain Behavior of High-Strength Concrete under Different FRP Confinement Stiffness Ratios
Publication: Journal of Composites for Construction
Volume 28, Issue 2
Abstract
The ratio of fiber-reinforced polymer (FRP) confinement stiffness to concrete strength (confinement stiffness ratio) has been widely accepted to determine the postpeak stress‒strain behavior of FRP-confined concrete. It has been established that the effects of confinement efficiency are significantly different for normal-strength concrete (NSC) and high-strength concrete (HSC). This paper presents an experimental study of the stress‒strain behavior of carbon FRP (CFRP)-confined circular and square HSC columns. Various FRP confinement stiffnesses were designed for concretes with different strengths to achieve the same confinement stiffness ratios. The test results indicate that although the specimens had similar confinement stiffness ratios, the criterion values of the confinement stiffness ratio to distinguish the postpeak strain hardening/softening transition increased with increasing HSC strength. However, for FRP-confined NSC, it is suggested that a constant value of approximately 6.5 be used. In addition, this study also revealed that for specimens with weak confinement or nonuniform confinement (square cross sections), the change in confinement efficiency at the postpeak stage results in the recovery of the postpeak strain hardening behavior from the strain softening behavior. By incorporating the confinement efficiency parameter in the ultimate condition models for CFRP-confined HSC, the proposed model demonstrated satisfactory performance when compared with the test results.
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Data Availability Statement
All raw data reported in this paper are contained within the manuscript.
Acknowledgments
The work described in this paper was financially supported by the National Natural Science Foundation of China (Grant No. 52078299), the Basic and Applied Basic Research Foundation of Guangdong Province (Grant No. 2023A1515011933), and the Shenzhen Science and Technology Program (Grant No. KQTD20200820113004005).
Notation
The following symbols are used in this paper:
- Ae
- effective confinement area of the column section (mm2);
- Ag
- gross area of the column section (mm2);
- b
- section width of square specimen (mm);
- bf
- width of an FRP strip (mm);
- D
- diameter of circular specimen (mm);
- de
- equivalent sectional dimension (mm);
- Ec
- elastic modulus of concrete (MPa);
- Ef
- Young's modulus of FRP (MPa);
- E2
- second slope of the stress‒strain curve (MPa);
- fcc
- confined concrete strength (MPa);
- fcu
- ultimate stress (MPa);
- fc0
- compressive strength of unconfined specimen (MPa);
- ffe
- actual rupture strength of FRP on the columns (MPa);
- fl
- ultimate FRP confining pressure (fl, rup, ffe);
- f30
- concrete strength of unconfined grade C30 concrete (MPa);
- h
- longer side of a rectangular column (mm);
- Kl
- confinement stiffness (MPa);
- kɛ
- strain reduction factor;
- n
- number of FRP layers (nf);
- r
- corner radius (mm);
- Sf
- relative content of silica fume;
- sf
- clear vertical spacing between adjacent the FRP sheets (mm);
- tf
- thickness of FRP (mm);
- wf
- width of FRP sheets (mm);
- ɛcu
- ultimate strain;
- ɛc0
- axial strain corresponding to unconfined concrete strength fc0;
- ɛcu0
- ultimate compressive strain of unconfined concrete;
- ɛfrp
- average rupture strain from coupon tests (ɛf);
- ɛh,rup
- average rupture strain;
- ρ
- confinement stiffness ratio; and
- ρg
- longitudinal steel reinforcement ratio.
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Published In
Journal of Composites for Construction
Volume 28 • Issue 2 • April 2024
Copyright
© 2024 American Society of Civil Engineers.
History
Received: Jun 26, 2023
Accepted: Dec 6, 2023
Published online: Jan 12, 2024
Published in print: Apr 1, 2024
Discussion open until: Jun 12, 2024
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Cited by
- Javad Shayanfar, Joaquim A. O. Barros, Design-Oriented Model of Unified Character to Determine Softening–Hardening Stress–Strain Behavior of FRP-Confined Concrete Columns of General Cross Section, Journal of Composites for Construction, 10.1061/JCCOF2.CCENG-4772, 28, 6, (2024).
- Peng-Da Li, Si-Jie Gao, Yu-Fei Wu, Stress Distribution in Concrete with Nonuniform Passive FRP Confinement, Journal of Composites for Construction, 10.1061/JCCOF2.CCENG-4727, 28, 6, (2024).