FRP Shear-Strengthened RC Beams: Re-examining the Shear-Crack Effect
Publication: Journal of Composites for Construction
Volume 26, Issue 5
Abstract
Inconsistency and large scatter are widely observed in comparisons between experimentally obtained and analytically predicted shear capacity contributed by fiber-reinforced polymer (FRP) composites in FRP-strengthened reinforced concrete beams using existing codes and models. Shear crack configuration, overlooked by many design codes, guidelines, and analytical models, can possibly attribute to such a scatter and inconsistency. To that end, an innovative analysis approach was proposed, in combination with a conducted experimental study, to investigate the effect due to such a shear crack configuration. It was found that large axial rigidity of the FRP reinforcement and the shear span-to-effective depth ratio tended to create distributed shear cracks, which changed the shear behavior of strengthened beams by decreasing the bond length and the resultant FRP shear contribution. The strain of the shear reinforcement increased with the increase of the crack width, which reached the peak value after the peak load level. Since not all steel stirrups yielded, the shear contribution of the concrete itself was greatly underestimated. It is suggested to propose separate sets of design equations corresponding to different categories of shear crack to improve the precision and minimize such a scatter.
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Acknowledgments
The work by the first author was supported by the Natural Science Foundation of China (Grant No. 52078297), Shenzhen Science and Technology Innovation Commission (Grant No. 20200805103111001), and Guangdong Provincial Key Laboratory of Durability for Marine Civil Engineering (SZU) (Grant No. 2020B1212060074). Any opinions, findings,conclusions, or recommendations expressed in this material do not necessarily reflect the views of the funding agencies.
Notation
The following symbols are used in this paper:
- Af
- area of the FRP reinforcement (mm2);
- Afi
- area of each FRP intersected by the shear crack (mm2);
- Asi
- area of each steel stirrup intersected by the shear crack (mm2);
- df
- effective depth of the FRP reinforcement (mm);
- Ef
- Young's modulus of the FRP reinforcement (GPa);
- compressive strength of concrete (MPa);
- K
- strengthening efficiency factor of FRP;
- R
- reduction factor for FRP rupture failure and debonding failure;
- sf
- spacing of the FRP reinforcement (mm);
- V
- overall shear capacity (kN);
- Vc
- concrete contribution to the overall shear capacity (kN);
- Vf0
- FRP contribution to the overall shear capacity (kN);
- Vs
- steel stirrup contribution to the overall shear capacity (kN);
- αf
- orientation of the FRP reinforcement with respect to the horizontal axis;
- γd
- member factor considering uncertainty and deterioration of the specimen;
- ɛfi
- strain of each FRP at intersection with the shear crack;
- ɛfu
- ultimate strain of the FRP shear reinforcement;
- ɛsi
- strain of each steel stirrup at intersection with the shear crack;
- θ
- acute angle between the FRP and the beam member axis;
- θc
- angle between the shear crack and the member axis;
- κv
- bond reduction coefficient considering the debonding failure between the FRP and concrete;
- ϕf
- resistance factor for FRP reinforcement; and
- ρf
- reinforcement ratio of FRP.
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Journal of Composites for Construction
Volume 26 • Issue 5 • October 2022
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© 2022 American Society of Civil Engineers.
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Received: Aug 12, 2021
Accepted: May 25, 2022
Published online: Aug 9, 2022
Published in print: Oct 1, 2022
Discussion open until: Jan 9, 2023
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