Experimental Investigation of Fatigue Shear Behavior of RC Beams Strengthened with FRP Bars Using Embedded Through-Section Technique
Publication: Journal of Composites for Construction
Volume 28, Issue 5
Abstract
This study presents the results of an experimental investigation of fatigue shear behavior in reinforced concrete (RC) beams strengthened with fiber-reinforced polymer (FRP) bars using the embedded through-section (ETS) technique. Thirteen ETS-FRP-strengthened beams were tested under two scenarios of medium-cycle fatigue (MCF) and high-cycle fatigue (HCF). The design variables were the number of stirrups, the FRP type, and the FRP size, and their effect on the fatigue characteristics of ETS-retrofitted RC beams was examined. The displacement and strain in flexural and shear reinforcement in the ETS-strengthened beams increased during the initial cycles and tended to stabilize during the rest of the fatigue process. Under MCF and HCF conditions, the fatigue stress ranges for longitudinal steel with ETS-FRP-strengthened beams satisfy the limits mandated in the American Association of State Highway and Transportation Officials code. Similar to previous studies, the maximum strain of 2,000 µɛ in the ETS-FRP strengthening systems can be considered the strain limit for the fatigue design of ETS-FRP-retrofitted beams. The use of glass FRP bars with a narrow spacing substantially extended the fatigue life of ETS-strengthened beams (to more than 3,000,000 cycles) compared with unstrengthened beams and beams retrofitted with carbon FRP bars. Conversely, a large number of stirrups reduced the contribution of ETS-FRP strengthening. The strength of the retrofitted beams increased with increasing FRP elastic modulus and bar diameter. Failure of ETS-FRP-strengthened beams under fatigue tests and static tests occurred in a safe and ductile manner because no rupture of the steel stirrups or the FRP bars occurred, and no early FRP debonding was observed.
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Data Availability Statement
All data, models, and codes generated or used during the study appear in the published article.
Acknowledgments
The authors acknowledge the resources and facilities provided by Tokyo City University. The authors also acknowledge the great assistance of the undergraduate and graduate students in the laboratories led by Professor Hidehiko Sekiya and Associate Professor Norihiko Kurihara. The authors are grateful for technical assistance from Tokyu Construction.
Notation
The following symbols are used in this paper:
- Af
- crossing area of FRP bars (mm2);
- As
- total cross-sectional area of the flexural reinforcement (mm2);
- Asw
- crossing area of two legs of a stirrup (mm2);
- a
- shear span length (mm);
- b
- beam width (mm);
- d
- effective depth of the beam section (mm);
- db
- ETS bar diameter (mm);
- Ef
- elastic modulus of the FRP bar (GPa);
- compressive strength of the concrete (MPa);
- fys
- yield strength of the longitudinal steel bars (MPa);
- fysw
- yield strength of a steel stirrup (MPa);
- h
- beam height (mm);
- kmax and kmin
- load percentages that define the imposed fatigue loading range;
- Pmax and Pmin
- maximum and minimum forces applied in the fatigue tests (kN);
- p
- bond curvature factor;
- sm
- slip at peak bond stress (mm);
- ssw
- stirrup spacing (mm);
- Vc
- shear resistance provided by the concrete (kN);
- Vf
- shear resistance provided by the ETS-FRP (kN);
- Vmax
- maximum shear force applied in the fatigue tests (kN);
- Vn
- total shear strength of the beams (kN);
- Vs
- shear resistance provided by the shear reinforcement (kN);
- VT
- beam shear capacity due to bending action (kN);
- β
- stirrup or ETS inclination angle (°);
- ɛef
- effective strain in the ETS-FRP system;
- θ
- crack angle (°), which is assumed to be 45°;
- ρl
- flexural reinforcement ratio;
- τm
- stress experienced by the bond between the ETS-FRP bar and the concrete (MPa);
- Δδ
- displacement difference (mm);
- Δɛ
- maximum strain range; and
- Δσ
- maximum stress range (MPa).
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Information & Authors
Information
Published In
Journal of Composites for Construction
Volume 28 • Issue 5 • October 2024
Copyright
© 2024 American Society of Civil Engineers.
History
Received: Aug 26, 2023
Accepted: May 7, 2024
Published online: Jul 12, 2024
Published in print: Oct 1, 2024
Discussion open until: Dec 12, 2024
ASCE Technical Topics:
- Beams
- Composite materials
- Concrete
- Concrete beams
- Engineering fundamentals
- Engineering materials (by type)
- Engineering mechanics
- Fatigue (material)
- Fatigue tests
- Fiber reinforced composites
- Fiber reinforced polymer
- Laboratory tests
- Material mechanics
- Material properties
- Materials engineering
- Polymer
- Reinforced concrete
- Structural behavior
- Structural engineering
- Structural members
- Structural strength
- Structural systems
- Synthetic materials
- Tests (by type)
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