Determining the Optimal Percentage of FRP Composite Bars in Hybrid Reinforced Beams

Reinforcing the concrete beams with the combination of steel and FRP composite bars improves the structural performance and long-term durability of these members significantly. Although hybrid steel-FRP (HSF) reinforced concrete (RC) beams have better structural behaviors than those members reinforced only with pure steel or pure FRP composite bars, no comprehensive research has been reported on determining the optimal percentage of steel and FRP composite bars in RC beams yet. Filling this gap is the main aim of the present study. To reach this aim, the sectional analysis of a series of HSF-reinforced concrete beams under different loading stages has been carried out, and the moment-curvature relationships in considered beams have been determined. Different values have been considered for the percentage of tensile steel, FRP composite, and compressive steel bars. Various values are also considered for the compressive strength of concrete, the yield stress of steel bars, and the mechanical properties of the FRP composite bars. To find suitable structural performance, the moment-curvature curves of concrete beams reinforced with HSF bars were compared with each other. Reducing residual deformations as well as increasing ductility are chosen as a criterion for determining the optimal percentage of steel and composite bars and other design parameters of the HSF-reinforced concrete beams. Results of this research show that the use of the optimum percentage of steel and FRP bars improves the flexural capacity, the desired ductility, and the corrosion resistance of the RC beams, and meanwhile, reduces the effects of residual deformations.

Keywords:

HSF-reinforced concrete beams , FRP composite bar , Steel bar , Residual deformation , ductility