An enhanced approach to assess the reduction of flexural ductility of reinforced/steel fiber reinforced concrete beams and slabs

Application of steel fibers in RC elements in protective structures decreases the damage caused under extreme loads but can lead to reduced ductility of beams and slabs with low conventional reinforcement. This paper presents an investigation of the effect of fibers on the flexural ductility, depending on the amount of conventional reinforcement, its mechanical properties, as well as cracking localization. The former parameters are integrated into a single variable, ρ_eff, where ρ_eff is a value determined as the product of longitudinal reinforcement ratio, ρ_s, and the quotient of the ultimate and yield strengths of rebars. It is shown that for a given amount of steel fibers, at low values of ρ_eff the ductility increases with increasing ρ_eff unlike plain RC flexural elements. It is also shown that a higher cracking localization level causes lower structural ductility. This correlation was observed only for low effective reinforcement ratios up to a certain transition point. Findings of this study suggest that in order to resolve this conflict and to guarantee sufficient ductility of R/SFRC flexural elements, their minimum reinforcement ratio should be increased, compared with the values given for plain RC beams and slabs.