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A bridged-crack model is proposed which reproduces the constitutive flexural response of reinforced concrete members with fibers. Two different reinforcements, the longitudinal bars(primary reinforcement) and the fibers(s econdary reinforcement) distributed in the brittle cementitiousmatrix are considered. The bridging actionsexerte d by the reinforcementsonto the crack facesar e assumed asrigid-p erfectly-plastic for the primary onesand as cohesive softening forces for the fibers.
From the dimensional analysis, it comes out that the constitutive flexural response depends on three dimensionless parameters. The first one, ˜E w˜c, controlsthe extension of the process zone. The other two parameters, called brittleness numbers N(1) P and N(2)
P , are related to the reinforcement phases. The role of the size scale is fundamental for the global structural behaviour, which can range from ductile to brittle simply with the variation of the two brittleness numbers, which are function for each reinforcement phase of matrix
toughness, reinforcement yielding or slippage limit, reinforcement volume fraction and global structural size.