Scale effects investigation on the mechanical behaviour of steel-fibre and steel-bar (hybrid) reinforced concrete beams

This study investigates the mechanical behaviour of steel-fibre and steel-bar (hybrid) reinforced concrete (HRC) beams including flexural cracking, shear, and flexural crushing failure modes in the framework of Fracture Mechanics by means of the Updated Bridged Crack Model (UBCM).The experiments are carried out via four-point bending tests on 300 beams (3 identical specimens per 100 different cases) with: (1) longitudinal steel-bar percentages of 0.00, 0.06, 0.13, 0.28, and 0.50%; (2) fibre volume fractions of 0.00, 0.10, 0.20, 0.40, and 0.80%; (3) beam depths of 20, 40, 80, and 160 cm; (4) slenderness ratio constant and equal to 6.The UBCM is applied to assess crack propagation and failure mechanisms in hybrid-reinforced concrete beams.The reinforcement brittleness numbers (NP and NP,f) and the pull-out brittleness number (Nw) are thoroughly studied, and the numerical results prove that a softening post-cracking response of the hybrid-reinforced concrete element emerges, and its mechanical performance results to be scale-dependent.The numerical analyses prove the strong interaction between the two design parameters: steel-bar percentage and fibre volume fraction.