Efficiency of hybrid reinforced concrete beams with low reinforcement ratios

This research explores the serviceability level characterization of hybrid reinforced concrete (HRC) beams with low reinforcement ratios in the range of 0.052%-0.262% under flexural test. Hybrid reinforced structural members use continuous reinforcement with randomly distributed chopped fibers in the matrix. The study focuses on the immediate post-cracking response of flexural beams to analyze parameters such as stiffness, deflection, strain transfer mechanisms, and ultimate strength response. The influence of steel fibers on flexure performance, ductility, and tensile strain, as well as the sharing of the flexural load are also studied. HRC beams are shown to have a higher first crack strength (15–24%) and stiffness in the serviceability domain compared to conventional RC beams regardless of the reinforcement ratio. The addition of up to 1.25% fibers contributes to the sharing of the flexural load such that reducing longitudinal reinforcement between 50 and 80% was associated with decreasing the ultimate load between 10 and 50% while still increasing the post-crack stiffness. Crack localization was found in both RC and HRC sections within a range of reinforcement ratios. The addition of fiber while maintaining the same reinforcement ratio confirmed the reduction in ductility. However, by adopting a lower limit of 3.0 for the deflection ductility ratio, HRC beams with up to 0.75% of steel fibers were found to be ductile, even despite presented softening behavior after the peak load.