FRP U-Wrap Anchorage for Preventing Concrete Cover Separation: Experimental Study and Design Method
Publication: Journal of Composites for Construction
Volume 26, Issue 4
Abstract
Fiber-reinforced polymer (FRP) systems are commonly used in the flexural strengthening of reinforced concrete beams. However, concrete cover separation (CCS) is one of the main debonding failure modes that negatively impact the strengthening efficiency. This premature failure mode occurs at a lower fraction of tensile strain capacity of the longitudinal FRP reinforcement. Placing FRP U-wrap anchorage at the end regions of FRP longitudinal plates appears to be a promising technique that could mitigate or prevent CCS. This study characterized, experimentally, the effect of FRP U-wraps in enhancing the strengthening efficiency by mitigating CCS in FRP-strengthened RC beams. The study included full-scale RC beams strengthened in flexure using FRP sheets and anchored at their ends using FRP U-wraps. The beams were simply supported and tested under four-point bending. The test variables were the width and layout of the FRP U-wraps. The test results indicate the effectiveness of FRP U-wraps in preventing CCS once the required area of U-wrap is provided. The paper also presents a proposed design method for quantifying the minimum area of FRP U-wrap anchorage required to prevent CCS. The proposed design method was verified using the test results obtained from this study and also from a database of beams reported in the literature. Based on the findings of the study, recommendations are suggested for the design of a FRP U-wrap anchorage system that is capable of preventing CCS in FRP-strengthened RC beams.
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Acknowledgments
The authors extend their appreciation to the Center of Excellence for Concrete Research and Testing (CoE-CRT), King Saud University, for funding this research study.
Notation
The following symbols are used in this paper:
- Af
- cross-sectional area of FRP longitudinal reinforcement;
- Afw
- cross-sectional area of FRP U-wrap;
- Afw,cal
- calculated cross-sectional area of FRP U-wrap;
- Afw,exp
- experimental cross-sectional area of FRP U-wrap;
- bf
- width of FRP longitudinal reinforcement;
- bfw
- width of FRP U-wrap;
- c
- depth of neutral axis;
- df
- depth of FRP longitudinal reinforcement;
- dfw
- effective bond length of FRP U-wrap;
- Ef
- tensile modulus of elasticity of FRP longitudinal reinforcement;
- Efw
- tensile modulus of elasticity of FRP U-wrap;
- specified compressive strength of concrete;
- fct
- tensile strength of concrete;
- ffu
- rupture stress of FRP longitudinal reinforcement;
- k1
- factor accounting for concrete strength;
- k2
- factor accounting for wrapping scheme;
- kv
- bond reduction coefficient;
- Le
- active bond length;
- nf
- number of longitudinal FRP plies;
- nfw
- number of FRP U-wrap plies;
- P
- total applied load;
- Pcr
- cracking load;
- Pu
- ultimate load;
- Pu,exp
- experimental ultimate load;
- Py
- yield load;
- Sfw
- spacing of FRP U-wrap;
- Tf
- maximum tensile force in FRP longitudinal reinforcement;
- Tsw
- tensile force in FRP U-wrap;
- tf
- thickness of one ply of FRP longitudinal reinforcement;
- tfw
- thickness of one ply of FRP U-wrap;
- ΔPu
- increase in experimental ultimate load of anchored beam with respect to control beam;
- δcr
- midspan deflection at cracking load;
- δu
- midspan deflection at ultimate load;
- δy
- midspan deflection at yield load;
- ɛbi
- strain in concrete substrate at time of longitudinal FRP installation;
- ɛc
- compressive strain of concrete;
- ɛcu
- crushing strain of concrete;
- ɛf
- tensile strain in FRP longitudinal reinforcement;
- ɛfd
- debonding strain of FRP reinforcement;
- ɛfu
- rupture strain of FRP longitudinal reinforcement;
- ɛfw,e
- design tensile strain in FRP U-wrap;
- ɛfw,u
- rupture strain of FRP U-wrap;
- ɛs
- tensile strain in steel reinforcement; and
- μ
- coefficient of friction.
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Published In
Journal of Composites for Construction
Volume 26 • Issue 4 • August 2022
Copyright
© 2022 American Society of Civil Engineers.
History
Received: May 5, 2021
Accepted: Feb 16, 2022
Published online: May 3, 2022
Published in print: Aug 1, 2022
Discussion open until: Oct 3, 2022
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