Not all steel fiber reinforced concrete composites are equally effective in enhancing structural performance. Their mechanical behaviour strongly depends upon the reinforcement morphology as well as the properties of the interface lying between steel reinforcement and concrete matrix. Using bone-shaped short (BSS) steel fibers, instead of conventional straight short (CSS) steel fibers, to reinforce concrete has demonstrated their potential in improving toughness, ductility and energy absorbing capacity under impact significantly and simultaneously. Accomplishing a strong steel-concrete interface leads to a slight increase in composite strength but simultaneously to a significant decrease in its toughness. Due to the sensitivity of steel reinforced concrete performance on these complex geometric and material parameters, the development of a numerical tool capable of simulating accurately the composite mechanical behaviour and thus leading to optimized design solutions is desirable. The physical problem of the present work involves a typical concrete composite uniformly reinforced with steel fibers subjected to tensional loading. A micromechanical non-linear finite element formulation is utilized in order to predict the load transfer characteristics and the failure process. A linear material behaviour is assumed for the steel component; a non-linear multi-crack material response is used to describe concrete while a mix-mode bilinear behaviour is utilized for the interface providing separation of primary material phases. Numerical results are presented in terms of the global design parameters. The influence of the fiber end shape, the interface strength and the fiber volume fraction on the composite strength and toughness is addressed and consequently optimized design preferences arise. (C) Koninklijke Brill NV, Leiden, 2010