On the bearing capacity of a redundant structure : the influence of mechanical characteristics scattering

Steel fibre reinforced concrete (SFRC) has been studied since late fifties. Diffused fibres can be used as partial or total substitution of conventional welded mesh reinforcement. The addition of fibres has shown to increase significantly the post-cracking tensile residual strength after the onset of the first cracking, due to the fibre mechanism of bridging on the cracks surfaces. Despite the huge amount of research investigations and the fast technological innovation, fibre reinforced concrete has met several difficulties to be considered, at all intends, as a building material. The main unsolved problem related to fibre reinforced material is the link between average and characteristic material properties. In fact, the large scattering, which affects the residual strength of the softening branch, can drastically reduce the characteristic value, vanishing the positive contribution of fibres addition to the matrix. The dispersion of behaviour of fibre reinforced concrete tests is considerably high and depends on fibres orientation and dispersion. On one hand, based on experimental evidences, standard tests, as three or four point bending, seem to be governed by characteristic strength. On the other hand, structural response guarantees higher reliability, due to volume size and the ability of the structure to redistribute stresses on the basis of its shape and boundary conditions. The aim of this thesis is to identify the effects of redundancy and structural size on the characteristic constitutive law for tension softening SFRC to adopt in the structure which has to be modeled. To reach this goal, several material and structural factors, affecting the post-peak response of SFRC structures, have been considered by means of experimental and numerical investigations.