In this study focuses on the review of strengthening structurally deficient reinforced concrete (RC) T-beams using externally bonded glass fiber reinforced polymer (GFRP) sheets. Rehabilitation of RC structures is essential due to aging, corrosion, construction defects, increased service demands, and seismic vulnerabilities. Among various beam configurations, T-beams are widely used in buildings and bridges, with shear failure being particularly catastrophic due to its sudden nature. Externally bonded FRP has emerged as a promising strengthening solution due to its high strength-to-weight ratio, corrosion resistance, and ease of installation. This research involved testing eleven full-scale RC T-beams under symmetrical four-point static loading to assess shear performance and failure modes. Key variables included the presence of steel stirrups, shear span-to-depth ratios, and the quantity of GFRP used. The results demonstrated a notable improvement in shear capacity with GFRP application. However, failure typically began with debonding of the FRP sheets, followed by brittle shear collapse. To address this issue and ensure full utilization of FRP strength, an innovative anchorage technique using GFRP plates was introduced, effectively preventing premature debonding. This method offers a more efficient, cost-effective alternative to traditional strengthening approaches and highlights the potential of FRP composites in structural rehabilitation.
Introduction
The civil engineering industry is adopting innovative materials and technologies to meet the demands of advanced infrastructure. As existing structures age and new standards rise, retrofitting becomes a cost-effective solution to enhance durability and safety against earthquakes and environmental forces, avoiding expensive full replacements.
The literature review focuses on rehabilitation strategies for reinforced concrete (RC) structures, highlighting fiber reinforced polymers (FRP) as a promising strengthening material. Studies are grouped into strengthening of RC rectangular beams, T-beams, and beams with web openings.
For RC rectangular beams, research shows that methods like integrating carbon-fiber-reinforced polymer (CFRP) bars, epoxy-bonded FRP sheets, and steel elements significantly improve load capacity, stiffness, and shear strength, though debonding remains a challenge.
For RC T-beams, CFRP composites, especially near surface mounted (NSM) laminates, enhance flexural and shear strength effectively. Innovative approaches such as FRP ropes and mechanically anchored dry carbon fiber sheets improve torsional and shear capacity, reducing typical failures like premature debonding.
For beams with web openings, which weaken shear capacity, studies suggest that pre-stressed shape memory alloy (Fe-SMA) bars and fiber reinforced concrete improve strength and control cracking. The impact of openings depends on size and position relative to load paths, with specific design guidelines developed for various opening shapes.
Conclusion
The following critical observations are made from the review of existing literature in the area of reinforced concrete (RC) beams strengthened with epoxy-bonded FRP
1) Most of the research efforts have been made to study the flexural and shear behaviour of RC rectangular beams strengthened with fiber reinforced polymer (FRP) composites.
2) Despite the growing number of field applications, there is limited number of reports on shear behaviour of strengthened RC T-beams using externally bonded FRP composites
3) A limited works have been reported on strengthening of RC T-beams with web openings.
4) There is a gain in shear capacity of RC beams when strengthened with FRP composites, peeling of FRP sheets from main concrete has been reported due to improper anchorage.
5) The study on anchorage system used for the prevention of debonding of FRP and concrete on shear behavior of RC beams is limited.
6) Many researchers are of the opinion that the previous design provisions do not have comprehensive understanding of the shear behavior.
References
[1] Alkhateeb, M. Y., & Hejazi, F. (2024). Strengthening Reinforced Concrete Beams through Integration of CFRP Bars, Mechanical Anchorage System, and Concrete Jacketing. Materials, 17(12), 2794. https://doi.org/10.3390/ma17122794
[2] Yu, T., Sun, Q., Li, C., & Liu, Y. (2021). Experimental Research on the Flexural Performance of RC Rectangular Beams Strengthened by Reverse-Arch Method. Symmetry, 13(9), 1666. https://doi.org/10.3390/SYM13091666
[3] Minchala Velecela, W. F., Naspud Uruchima, P. R., Nieto-Cárdenas, J. X., & Illescas-Cárdenas, P. (2024). Reinforcement concrete beams with external steel elements. Green World Journal, 7(1), 117. https://doi.org/10.53313/gwj71117
[4] Mallikarjuna, K., Parkhe, R., Muhmmad, D., Mohammad, A. K., & Saiful, I. (2023). Employing Carbon Fiber Reinforced Polymer Composites toward the Flexural Strengthening of Reinforced Concrete T-Beams. ACS Omega, 8(21), 18830–18838. https://doi.org/10.1021/acsomega.3c00988
[5] Zapris, A. G., Kytinou, V. K., Xynopoulos, I., Gribniak, V., & Chalioris, C. E. (2024). Innovative torsional strengthening of rc t-beams using nsm frp ropes. Proceedings of International Structural Engineering and Construction. https://doi.org/10.14455/10.14455/isec.2024.11(2).str-30
[6] Alobaidi, H. E., & Al?Zuhairi, A. H. (2023). Structural Strengthening of Insufficiently Designed Reinforced Concrete T-Beams using CFRP Composites. Civil Engineering Journal, 9(8), 1880–1896. https://doi.org/10.28991/cej-2023-09-08-05
[7] Khalil, A., Elkafrawy, M., Hawileh, R. A., & AlHamaydeh, M. (2024). Numerical Investigation on Improving Shear Strength of RC Beams with Various Web Opening Shapes Using Pre-Stressed Fe-SMA Bars. Key Engineering Materials, 1004, 13–22. https://doi.org/10.4028/p-e2xiev
[8] Alex L., Assih J., and Delmas Y. (2001), “Shear Strengthening of RC Beams with externally bonded CFRP sheets”, Journal of Structural Engineering, Vol. 127, No. 4, Paper No. 20516.
[9] Balamuralikrishnan R., and Jeyasehar C. A. (2009), “Flexural behaviour of RC beams strengthened with Carbon Fiber Reinforced Polymer (CFRP) fabrics”, The Open Civil Engineering Journal, 3, 102-109.
[10] Bousselham A., and Chaallal O. (2006), “Behavior of Reinforced Concrete T-beams strengthened in shear with carbon fiber-reinforced polymer –An Experimental Study”, ACI Structural Journal, Vol. 103, No. 3, pp. 339-347.
[11] Ceroni F. (2010), “Experimental performances of RC beams strengthened with FRP materials”, Construction and Building materials, 24, 1547-1559.
[12] Chaallal O., Nollet M. J., and Perraton D. (1998), “Strengthening of reinforced concrete beams with externally bonded fibre-reinforced-plastic plates: design guidelines for shear and flexure”, Canadian Journal of Civil Engineering, Vol. 25, No. 4, pp. 692-704.
[13] Chen J. F., and Teng J. G. (2003), “Shear capacity of FRP-strengthened RC beams: FRP debonding”, Construction and Building Materials, 17, 27-41.
[14] Chen J. F., and Teng J. G. (2003), “Shear capacity of Fiber-Reinforced Polymer- Strengthened Reinforced Concrete Beams: Fiber Reinforced Polymer Rupture”, Journal of Structural Engineering, Vol. 129, No. 5, ASCE, ISSN 0733-9445, pp. 615-625.
[15] Deifalla A., and Ghobarah A. (2010), “Strengthening RC T beams subjected combined torsion and shear using FRP fabrics Experimental Study”, Journal of Composites for