Design Propositions for Hybrid FRP-Steel Reinforced Concrete Beams

Concrete beams reinforced with a combination of steel and fiber-reinforced polymer (FRP) bars can provide increased strength, serviceability, and durability. However, the amounts of FRP and steel necessary to ensure sufficient strength and ductility are unclear. Because of the linear elastic behavior of FRP bars before failure, the deformation characteristics of hybrid reinforced concrete beams differ from those of conventional steel reinforced concrete beams and pure FRP reinforced concrete beams. Conventional ductility indices are not suitable for concrete beams in hybrid reinforcement approaches. To ensure the ductile failure of beams, proper reinforcement ratio limits are proposed. In addition, a new ductility index is defined in terms of deformability and energy absorption capacity. Various comparisons between experimental results and theoretical predictions show that the developed models can accurately predict the load capacity and ductility. In addition, the influences of various parameters on ductility are discussed. Based on various requirements for ductility, reasonable ratios of FRP to steel bars are found.