Flexural Behaviour Analysis of Hybrid Steel-GFRP Reinforced Concrete Members

Plain concrete, which is strong in compression but weak in tension, has historically been reinforced with steel bars to withstand tensile stresses, resulting in Reinforced Concrete (RC). In the last decades, studies and research investigated a wide range of reinforcement alternatives, including composite materials, like Glass Fiber-Reinforced Polymer (GFRP), mainly because of the growing problem of corrosion of steel bars in ordinary RC elements and related maintenance problems with consequent high costs. The introduction of GFRP reinforcing bars in RC structural elements provides several advantages such as high resistance to corrosion, high tensile strength, light weight, electromagnetic transparency and sustainability, making them particularly suitable for harsh environments and retrofitting applications. However, GFRP bars show a brittle behaviour, limiting their use in seismic areas where energy dissipation and ductility are required. By combining the ductility of steel with durability and resistance to corrosion of GFRP, the resulting hybrid steel-GFRP RC elements can optimize both strength and performances. This approach is applicable to the retrofitting of existing structures as well as to the design of new ones. Nowadays there are no regulations regarding the design of structural elements with such a hybrid reinforcement. The purpose of this research is to point out advantages at the Ultimate Limit State (ULS) of designing repairing/strengthening interventions, such as concrete jacketing, utilizing a novel retrofitting technology using hybrid steel-GFRP reinforcement. Design models are proposed based on fundamental RC beam theories and existing research on failure mechanisms of GFRP reinforced sections. Cross-sectional analysis is used to investigate various solutions and assess the improvement in load bearing capacity and ductility in the bending regime.