Fibrous reinforced concrete beams in flexure: Experimental investigation, analytical modelling and design considerations

The flexural behavior of plain and fibrous reinforced concrete (FRC) beams under monotonic and cyclic actions was analysed. Twelve beams were reinforced with top and bottom longitudinal deformed steel bars and transverse steel stirrups. Concrete, having 30 MPa cylindrical strength, was reinforced with hooked steel fibres at a volume percentage of 1%. Beams, 600 mm in length and with a square side cross-section of 150 mm, were tested in flexure using a three point bending test, adopting three different cover thicknesses of 5, 15 and 25 mm, respectively. The results obtained show that the addition of fibers increases the bearing capacity of the beams and ensures more ductile behaviour, at the same time reducing degradation effects under cyclic reversal loads. Moreover, the presence of fibers reduces the cover spalling process, also in the presence of high cover thicknesses. Shear strength of the beams was calculated using an analytical expression given in literature for plain concrete beams and here extended to the case of fibrous concrete beams of hooked steel fibers on the subject, while the analytical results in terms of load–deflection curves, under monotonic actions, were generated using a non-linear finite element program (DRAIN-2DX). This program was calibrated on the basis of constitutive laws in compression and in tension capable of taking FRC properties into account, and verified against experimental data. Finally, practical considerations regarding the choice of the optimum geometrical ratio of longitudinal and transverse steel bars for the ductile behaviour of single reinforced cross-sections. Moreover shear strength are given and compared with European and International code prescriptions.