Strength Model for Debonding Failure in RC Beams Flexurally Strengthened with NSM FRP and Anchored with FRP U-Jackets
Publication: Journal of Composites for Construction
Volume 27, Issue 5
Abstract
The flexural performance of reinforced concrete (RC) beams could be effectively improved by applying a near-surface mounted (NSM) fiber-reinforced polymer (FRP) at the beam soffit. However, such NSM FRP flexurally-strengthened beams frequently failed due to FRP debonding, which limited the full utilization of the FRP strength. In some experimental studies, FRP U-jackets have been used as the anchorage to mitigate or prevent debonding failures in NSM FRP flexurally-strengthened beams. These studies showed excellent anchoring performance of the FRP U-jackets. The authors recently developed a finite-element (FE) approach that could accurately predict the behavior of RC beams that had been flexurally strengthened with NSM FRP (NSM-strengthened beams), which were anchored with FRP U-jackets. Based on a parametric study that was undertaken, which used the simplified version of the FE approach, this paper proposed a strength model for the most common debonding failure mode in NSM-strengthened beams with FRP U-jackets. The proposed strength model consisted of an equation for the maximum NSM FRP strain (ɛf) at debonding failure. Once the maximum FRP strain was known, the load-carrying capacity of the strengthened beam could be obtained through a section analysis. Comparing the predictions made by the proposed strength model with the test results showed that the proposed strength model could provide close predictions.
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Data Availability Statement
All data, models, and codes generated or used during this study appear in the published article.
Acknowledgments
The authors are grateful for the financial support from the National Natural Science Foundation of China (Projects No. 51878310 and No. 52078231) and the Key Research and Development Program of Hubei Province of China (Project No. 2021BCA150).
Notation
The following symbols are used in this paper:
- Af
- cross-sectional area of NSM FRP;
- b
- width of beam;
- bg
- cross-sectional width of groove;
- Cg
- cross-sectional perimeter of groove;
- Dt
- sum of tension steel bar diameters;
- Ef
- elastic modulus of NSM FRP;
- Es
- elastic modulus of steel bars;
- Euj
- elastic modulus of FRP U-jackets;
- fc
- compressive strength of concrete (cylinder);
- fuj
- tensile strength of FRP U-jackets;
- yield strength of longitudinal compression steel bars;
- yield strength of longitudinal tension steel bars;
- h
- height of beam;
- he
- effective height of beam (i.e., the vertical distance between axis of longitudinal tension steel bars and top surface of beam);
- hg
- cross-sectional height of groove;
- Lc
- clear span of beam;
- Les
- embedded length of NSM FRP in shear span of beam;
- Lsh
- shear span of beam;
- ncom
- number of longitudinal compression bars;
- nten
- number of longitudinal tension steel bars;
- nuj
- number of FRP U-jackets;
- PFE
- predicted load-carrying capacity of beam that used full FE approach;
- PSFE
- predicted load-carrying capacity of beam that used simplified FE approach;
- PTest
- load-carrying capacity of beam from the test;
- tuj
- nominal thickness of FRP U-jackets;
- Wu
- U-jacket distribution width;
- Wuj
- U-jacket width;
- Wue
- effective U-jacket distribution width;
- Wus
- sum of U-jacket spacings;
- α0
- ratio of τdb,min to τdb,e;
- βr
- reduction factor related to sum of steel tension bar diameters-to-beam width ratio;
- βu
- reduction factor related to U-jacket distribution width;
- βus
- reduction factor related to U-jacket spacing;
- ɛdb
- maximum tensile strain in NSM FRP at debonding failure of beam;
- θuj
- U-jacket inclination angle;
- σdb
- maximum tensile stress in NSM FRP at debonding failure of beam;
- σc
- compressive stress of concrete;
- σf
- tensile stress of NSM FRP;
- λ
- shear span ratio;
- τdb
- average NSM FRP–concrete interfacial shear stress in shear span at debonding failure of beam;
- τdb,e
- average NSM FRP–concrete interfacial shear stress in shear span at debonding failure of beam that corresponded to effective U-jacket distribution width;
- τdb,min
- average NSM FRP–concrete interfacial shear stress in shear span at debonding failure of beam corresponding to a U-jacket distribution width of 50 mm;
- τf
- shear stress at NSM FRP–concrete interface;
- ϕcom
- diameter of longitudinal compression steel bars; and
- ϕten
- diameter of longitudinal tension steel bars.
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Information & Authors
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Published In
Journal of Composites for Construction
Volume 27 • Issue 5 • October 2023
Copyright
© 2023 American Society of Civil Engineers.
History
Received: Nov 7, 2022
Accepted: May 4, 2023
Published online: Jun 20, 2023
Published in print: Oct 1, 2023
Discussion open until: Nov 20, 2023
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