Strengthening of Reinforced Concrete Beams Using FRP Composites: A Review

Abstract

Reinforced concrete (RC) structures are prone to gradual deterioration over time, influenced by factors such as increased service loads, exposure to highly aggressive environmental conditions, and the natural aging of materials. Among the various retrofitting techniques available, the use of Fiber-Reinforced Polymers (FRP) externally bonded composite materials has proven to be one of the most effective solutions for restoring or even enhancing the structural performance of such elements. This paper presents a thorough review of over sixty experimental, analytical, and numerical studies focused on the application of FRP composites in strengthening RC beams. It critically examines advancements in FRP technology, material characteristics, and key parameters such as fiber type, orientation, bonding configuration, and failure mechanisms. Additionally, significant attention is given to finite element modelling (FEM) approaches and model-selection strategies employed to simulate the structural behaviour of FRP-strengthened beams. Key challenges, including nonlinear material modelling, bond behaviour at interfaces, and premature debonding issues, are addressed. The paper also highlights essential research directions needed to develop reliable performance-based design and analysis frameworks.

Introduction

The text presents a comprehensive review of the use of Fiber-Reinforced Polymer (FRP) composites for strengthening and retrofitting reinforced concrete (RC) beams, addressing deterioration caused by aging, corrosion, poor detailing, and increased service loads. Traditional strengthening methods such as steel jacketing add weight and are prone to corrosion, leading to the adoption of FRP composites since the late 1980s due to their high strength-to-weight ratio, corrosion resistance, durability, and ease of installation. FRP strengthening has been widely validated through experiments and incorporated into international design guidelines such as ACI 440R and FIB Bulletin 14.

The review synthesizes findings from over sixty experimental, analytical, and numerical studies (1987–2010), focusing on material properties, strengthening configurations, failure mechanisms, and modelling techniques. Common FRP types—CFRP, GFRP, AFRP, and BFRP—are discussed, highlighting their mechanical properties, advantages, limitations, and cost–performance trade-offs. CFRP offers the highest stiffness and strength and is preferred for critical applications, while GFRP is more economical but less stiff. AFRP provides high impact resistance but requires environmental protection, and BFRP is emerging as a sustainable alternative.

Experimental investigations consistently show that FRP strengthening significantly improves flexural strength, shear capacity, stiffness, crack control, and serviceability of RC beams. However, the dominant failure modes are premature FRP debonding and concrete cover separation, rather than rupture of FRP fibers. These findings emphasize that FRP–concrete interfacial bond behaviour governs ultimate performance.

The paper reviews analytical approaches, ranging from elastic transformed-section methods (ACI 440) suitable for serviceability analysis to advanced nonlinear fracture-mechanics-based models that incorporate bond–slip behaviour and effective bond length concepts. These advanced models better predict debonding failures and have influenced modern strain-based design limits.

Finite Element Modelling (FEM) is identified as a critical tool for simulating global and local behaviour of FRP-strengthened RC beams. FEM enables detailed analysis of stress redistribution, cracking, and interfacial debonding, offering accurate serviceability predictions and cost-effective virtual testing. However, model accuracy depends strongly on material assumptions and bond laws, and nonlinear FEM requires significant computational effort and experimental validation.

Conclusion

Improved anchorage systems and interface engineering are expected to play a major role in future research aimed at debonding prevention. Not only that, but also ductility oriented strengthening strategies like hybrid FRP–steel systems and pre stressed FRP laminates should be developed as an absolute necessity. It is still not very clear how long the materials would last under different conditions such as environmental exposure, fatigue, and sustained loading, thus requiring a thorough investigation. In addition to that, unified bond–slip and failure models are necessary to support performance-based design and increase reliability. Overall, the review concludes that FRP composites are among the most reliable and effective solutions for strengthening RC beams, while highlighting the need for continued research on bond behaviour, durability, anchorage systems, and performance-based design frameworks to further improve analytical and numerical prediction methods.

References

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Copyright

Copyright © 2026 Vikrant Dhoke, Dr. Monika Jain. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.