Experimental and numerical investigation on postcracking behavior of steel fiber reinforced concrete

This paper presents an experimental and numerical investigation on the postcracking strength, energy absorption and fracture energy of steel fiber reinforced concrete (SFRC). The aim of the conducted research was a study on the effect of fiber type, fiber dosage and specimen size on the postcracking behavior of steel fiber reinforced concrete. Another objective was the development of a numerical fitting procedure being able to deliver stress–strain relations in tension for a given experimental test. For this purpose, a failure pattern based on plastic hinge and yield line theory is considered and subsequently the experimental force–deflection curves are fitted through an numerical optimization procedure. In a first step, experimental investigation on 4-point bending beam specimens following an SFRC design recommendation as well as on large scale plates has been conducted. These results give first impressions on the evolution of bearing forces and energy absorptions under different material and geometry conditions. It could be demonstrated that both maximal force and total energy absorption increase when fiber dosage increase. Furthermore, a higher fiber aspect ratio has a positive effect on the mentioned characteristics, too. In a second step, a parametric optimization procedure has been performed with the simulation code on two postcracking constitutive laws in tension, assuming either an exponential or a tangent hyperbolic decreasing stress evolution with growing tensile strain. It is shown that a hyperbolic relation offers a more accurate overall approximation of the experimental curves, although the exponential law offers higher precision at small deflection levels. For both, evaluation of fracture energy reveals similar values and trends, and the comparison between different specimen sizes reveals a size effect resulting in lower tensile strength and fracture energy values when dealing with large scale specimens.