Crack Patterns in Reinforced and Fiber Reinforced Concrete Structures

Abstract

The cracking phenomenon of members made of traditional reinforced concrete (RC) or by combining steel fibers and traditional reinforcing bars (R/FRC) is analyzed in this paper. Referring to the tensile zone of a beam subjected to bending moment and axial load, a unique block model is introduced to predict crack widths, crack lengths and crack distances. The proposed approach, based on the nonlinear behaviour of the cracked cement-based material in tension, and on the bond-slip interaction between rebars and concrete, provides crack patterns similar to those observed in different experimental campaigns. Cracks in R/FRC beams are generally narrower, and originate at small distances, than those observed in RC beams having the same geometry and reinforcement ratio. This is entirely due to the presence of fibers, here considered through the Reinforcing Index, which is the product of volume percentage and fiber aspect ratio. However, the beneficial effect of fiber-reinforcement vanishes with the increase of structural dimension. Thus, in the case of massive structures, it appears necessary a direct calculation of the crack width, even in the presence of fibers.

A unified approach for determining the strength of Frc members subjected to torsion—Part I: Experimental investigation

“…For the FRC beams without stirrups and reinforced with Ø18 longitudinal bars, the crack spacing appears proportional to the FRC toughness, which is related to the fiber content. As observed in other studies, 42–44 an increase in the supplied fiber dosage in lightly reinforced FRC elements leads to a reduction of the average spacing of cracks. Averaging the two values of s v obtained for the beams containing 50 kg/m 3 of fibers “D” and “G” gives the average crack spacing equal to 128 mm and 168 mm, respectively.…”