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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.