Ductility Assessment of Hybrid FRP–Steel RC Beams Using Analytical Modeling
Abstract
This study aims to identify the most appropriate ductility definition for hybrid reinforced concrete (RC) beams combining fiber-reinforced polymer (FRP) and steel reinforcement. Although FRP bars are increasingly used due to their high corrosion resistance and tensile strength, their brittle failure mechanism limits ductility, which is critical for structural safety, especially under seismic or overload conditions. Hybrid reinforcement (FRP+steel), integrating the ductility of steel with the durability of FRP, has been proposed to mitigate this limitation. However, the literature lacks consensus on a standardized ductility definition suitable for such hybrid systems. An extensive experimental dataset of hybrid, FRP-only, and steel-only RC beams was analyzed using multiple ductility definitions from the literatüre to address this gap. Among these, the energy-based definition provided the most consistent and realistic representation of ductile behavior, capturing the elastic-brittle nature of FRP and the yielding response of steel. The selected definition was then extended to additional hybrid RC beams reported in the literature to assess its broader applicability. The analysis confirmed that the ratio of steel reinforcement to total tensile reinforcement (As/Atot) significantly influences ductility. A higher As/Atot ratio and co-location of FRP and steel in the same tensile layer consistently yielded more favorable ductile responses.
Keywords
Ductility, hybrid beams, reinforced concrete, fiber reinforced polymer
References
- Abdelrahman, A. A., Tadros, G., & Rizkalla, S. H. (1996). Test model for the first Canadian smart highway bridge. ACI Structural Journal, 92(1), 1–10.
- ACI Committee 440. (2015). Guide for the design and construction of structural concrete reinforced with fiber-reinforced polymer (FRP) bars (ACI 440.1R-15). American Concrete Institute.
- Aiello, M. A., & Ombres, L. (2002). Structural performances of concrete beams with hybrid (fiber-reinforced polymer–steel) reinforcements. Journal of Composites for Construction, 6(2), 133–140. https://doi.org/10.1061/(ASCE)1090-0268(2002)6:2(133)
- Bencardino, F., Condello, A., & Ombres, L. (2016). Numerical and analytical modeling of concrete beams with steel, FRP and hybrid FRP-steel reinforcements. Composite Structures, 140, 53–65. https://doi.org/10.1016/j.compstruct.2015.12.045
- Comité Européen de Normalisation (CEN). (2004). Eurocode 2: Design of concrete structures – Part 1-1: General rules and rules for buildings (prEN 1992-1-1). European Committee for Standardization.
- CSA. (2010). Canadian highway bridge design code (CSA S6-10). Canadian Standards Association.
- Dönmez, E. T., & Başaran, B. (2021). Bond Strength of Epoxy Impregnated Carbon Fiber Wrapped Steel Reinforcement. International Journal of Engineering Research and Development, 13(2), 625-634.
- El Refai, A., Abed, F., & Al-Rahmani, A. (2015). Structural performance and serviceability of concrete beams reinforced with hybrid (GFRP and steel) bars. Construction and Building Materials, 96, 518–529. https://doi.org/10.1016/j.conbuildmat.2015.08.063
- Ge, W., Zhang, J., Cao, D., & Tu, Y. (2015). Flexural behaviors of hybrid concrete beams reinforced with BFRP bars and steel bars. Construction and Building Materials, 87, 28–37. https://doi.org/10.1016/j.conbuildmat.2015.03.113
- Grace, N. F., Soliman, A. K., Abdel-Sayed, G., & Saleh, K. R. (1998). Behavior and ductility of simple and continuous FRP reinforced beams. Journal of Composites for Construction, 2(4), 186–194. https://doi.org/10.1061/(ASCE)1090-0268(1998)2:4(186)