Effect of bar diameter on the behavior of lightly reinforced concrete beams

The transition from the uncracked to the cracked phase in lightly reinforced concrete beams was experimentally investigated by subjecting five full-scale beams to three-point bending. All beams had the same dimensions and the same percentage of flexural reinforcement, but varying diameters and number of reinforcing bars. By means of transducers, strain gauges, and geometric moiré, the crack profiles and the concrete strain field around the cracks were measured. In this way, it was possible to observe and to reproduce numerically the crack onset and its stable propagation up to the unstable behavior that follows the effective cracking moment. During the growth of the crack, the moment rotation diagrams, the values of tensile strains in concrete, and the shape of crack profiles demonstrate the dependence of the mechanical response on bar diameter. Consequently, to avoid brittle failure, the minimum reinforcement ratio for lightly reinforced concrete beams should likewise be a function of bar diameter.