Behavior of Fibre Reinforced Concrete beams under cyclic loading

The behavior of composite concrete sections reinforced with conventional steel bars and steel fibers, and subjected to flexural cyclic loading beyond the yield point of steel bars, is analyzed by means of a mechanical model. The stress-strain relationships for the concrete, for the steel fiber, and for the steel bars are assumed to be piecewise linear. These constitutive laws are used to obtain the primary moment-curvature relationship of the section for a monotonically increasing load up to failure. On this basic curve, the successive stiffness degradation is created as a function of stress and strain levels reached in the section at each load cycle. Strain hardening of steel and the combined effect of confinement ensured by the stirrups and metal fibers are also taken into account. The numerical results, obtained at first for ordinary reinforced concrete sections, are compared with experimental results available in literature. Subsequently, the model is applied to study concrete sections reinforced with steel bars and steel fibers, subjected to a flexural cycle, with identical mechanical and geometrical specifications to the reinforced concrete sections. The equality of the maximum curvature reached to each load cycle for both kinds of sections is imposed, and comparisons are drawn in terms of energy dissipation.