Tension stiffening effect on rebars embedded in concrete prisms are investigated through computational as well as analytical methods and compared with experimental results. Both metallic (steel) and non-metallic (polyolefin and carbon) fibres of different dimensions are used in high-strength concrete. The softening behaviour of concrete determined by a uniaxial tensile procedure, was used in FEM and analytical models. The tension stiffening effect may be more dependent on the tensile behaviour of the concrete than on a relative slip between rebar and concrete