Experimental and Analytical Study of Cracking Localization in R/SFRC Beams and Its Effect on the Flexural Ductility

This paper presents an experimental study aimed to identify and quantify the cracking localization (CL) phenomenon in reinforced concrete beams with steel fibers (R/SFRC beams). Experimental results were used for quantification of the cracking localization level (CLL) considering the effect of fiber content, longitudinal reinforcement ratio, as well as the effect of the rebar yield and ultimate strengths. The experiments consisted of four-point bending tests of normal strength R/SFRC beam specimens with 400 and 500-MPa steel and fiber volumetric contents of 0.5 and 0.76%. The effect of conventional reinforcement ratio and its mechanical properties, as well as CLL, on the flexural displacement capacity (ductility) of R/SFRC beams is examined. The rebar properties are represented by a single parameter denoted ρ_ef that equals to the reinforcement ratio multiplied by the maximum-to-yield strengths ratio. Findings show that there exists a transition point of ρ_ef, below which ductility decreases (in contrary to plain RC behavior) and that higher CLL causes lower ductility. A probabilistic model, explaining the CL phenomenon, is presented. The fiber distribution in the structural member is considered random while the conventional reinforcement - deterministic. The model considers both the fibers and conventional reinforcement ratios, as well as the steel stress hardening and the location of the rebars in the cross-section. This study leads to the conclusion that in order to guarantee proper ductility of R/SFRC beams their minimum reinforcement ratio should be increased compared to plain RC beams.