Self Restrained Cracking of Reinforced Concrete Elements

It is widely considered as almost impossible to avoid cracking of concrete in a common structure under service loads: a variety of reasons contribute to develop cracking, but the main principle is that concrete is a quasi-brittle material with a low capacity for deformation under tensile stress. Nevertheless, even in the cracked state, concrete can provide its contribution in terms of stiffness due to the non damaged material laying between the cracks. Tensile stresses can either be a result of external load acting on the concrete structure or due to restrained endogenous deformations. Even though cracking in concrete does not usually affect the structural capacity, its negative effect on durability asks for a correct prediction and an adequate control of the phenomenon. Commonly used design methods, which are conceived principally for direct actions, give unsatisfactory prediction of the crack opening and spacing when structures are subjected to imposed deformations, such as massive castings or other highly restrained structures. In order to study the cracking process due to restrained deformations, a set of non-linear analysis on simple tie models is performed using the Finite Element Method. Crack spacing and crack widths are measured as a mean of comparison between cracking deriving by direct actions and by imposed deformations. Finally, the results of this study are compared with the provisions of the most common codes.