Experimental investigation of cracking localization in RC beams with steel fibers

This article presents an experimental study aimed to identify and quantify the cracking localization (CL) phenomenon in under-reinforced R/SFRC beams. Results of current experiments together with those of previous tests published by the authors were used for quantification of the cracking localization level (CLL) considering the effect of fiber content, V-f, and of longitudinal reinforcement ratio, rho (s), over a wide range of rho (s) and the effect of rebar yield and ultimate strengths. The experimental program consisted of four-point bending tests of normal strength R/SFRC beam specimens with 400 and 500-MPa steel and fiber volumetric contents V-f of 0.5 and 0.76%. A new definition is introduced for "significantly wide cracks" that yields a unique definition of the CLL when this phenomenon diminishes. Moreover, it is now proposed to change the definition of CLL. The study identified the existence of a transition point (TP), beyond which addition of fibers to the concrete mix do not affect CLL anymore. Observations from the experimental results prove the consistency of the newly proposed CLL definitions as well as the dependency of CL on both the amount and stress hardening of the tension steel. Their use enables a clear delineation of the CL phenomenon in R/SFRC beams. The importance of this finding refers to the reported decrease of flexural ductility in R/SFRC beams due to high CLL. Hence, the importance of the ability, achieved in the current findings, to quantify the conditions for TPs in various cases