Effectiveness of Fiber Anchors in CFRP Flexural Strengthening of RC Girders
Publication: Journal of Composites for Construction
Volume 28, Issue 4
Abstract
This research presents an experimental program for flexural strengthening of reinforced concrete (RC) full-scale girders with externally bonded carbon fiber–reinforced polymer (CFRP) sheets secured with fiber anchors. The testing program consisted of five RC T-girders strengthened with identical CFRP sheets anchored with different numbers of CFRP fiber bundles. The main objective of this study is to address the effectiveness of the CFRP fiber anchors in controlling premature failure of the CFRP sheets due to debonding. To evaluate the experimental results, a simplified design model was introduced to predict the effective CFRP maximum strain limit associated with a given number of fiber anchors in the shear span. The test results show that using CFRP fiber anchors significantly delayed the failure of the CFRP sheet beyond the classical intermediate crack (IC) debonding failure mode. In addition, the presented design model agrees reasonably well with the experimental findings as it pertains to the various numbers of anchors. Nevertheless, an anchor efficiency factor is proposed herein to reflect the fiber anchor group effect based on the experimental findings.
Practical Applications
This paper presents an experimental program and a design model to capture the efficiency improvements of the response of carbon fiber–reinforced polymer (CFRP) strengthened full-scale reinforced concrete T-girders secured with increasing number of carbon fiber anchors along the shear span. Both the equivalent debonding strain and load capacity were improved owing to the use of increasing numbers of fiber anchors per shear span. This study showed that the ultimate failure of the girders can be controlled by the number of fiber anchors used to secure the CFRP sheets. Sectional analysis may not be strictly applicable once the progression of debonding starts. However, it is shown to capture a reasonably accurate measure of the maximum CFRP debonding strain without the need to resort to higher-order analysis that does not lend itself to design practice.
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Data Availability Statement
Some data and models that support the findings of this study are available from the corresponding author upon reasonable request. Specifically, the experimental load–deflection data and the calculations related to the proposed model will be made available upon request.
Acknowledgments
The authors would like to acknowledge the Kansas Department of Transportation and Structural Technologies, Inc. for funding this project through Grant Numbers KTRAN-KSU-19-03 and ST-KSU-19-1. Structural Technologies, Inc. is further acknowledged for donating the FRP material. In addition, the authors are grateful to the research technologists Cody Delaney for helping manage the building of the girders and Ben Thurlow for setting up the girders and running the testing equipment at Kansas State University.
Notation
The following symbols are used in this paper:
- Av
- cross-sectional area of fiber anchor;
- bf
- width of CFRP sheet;
- diameter of the anchor;
- Ef
- longitudinal modulus of elasticity of CFRP sheet;
- G12
- in-plane shear modulus of CFRP;
- n
- number of anchors per shear span;
- nf
- number of CFRP sheets;
- Tmax
- maximum total tension force;
- tf
- thickness of CFRP sheet;
- Vmax_a
- maximum shear capacity of a single anchor;
- γmax_a
- critical shear strain (or kink angle);
- effective strain of CFRP sheet at debonding;
- ultimate fracture strain of CFRP;
- κɛ
- strain efficiency factor; and
- τmax_a
- shear stress of a single fiber anchor.
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Information & Authors
Information
Published In
Journal of Composites for Construction
Volume 28 • Issue 4 • August 2024
Copyright
© 2024 American Society of Civil Engineers.
History
Received: May 5, 2023
Accepted: Mar 18, 2024
Published online: May 30, 2024
Published in print: Aug 1, 2024
Discussion open until: Oct 30, 2024
ASCE Technical Topics:
- Anchors
- Carbon fibers
- Concrete
- Engineering fundamentals
- Engineering materials (by type)
- Equipment and machinery
- Fiber reinforced concrete
- Fiber reinforced polymer
- Fibers
- Flexural strength
- Material mechanics
- Material properties
- Materials engineering
- Polymer
- Reinforced concrete
- Strength of materials
- Synthetic materials
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