The paper presents an analytic al non linear method to evaluate the ultimate strain of the confined concrete columns so modifying the Braga-Laterza linear model approach. The analytical method has put in evidence several remarks on the influence of geometrical and mechanical properties; these results have been compared whit the results given by the semiempirical methods (e.g., Scott et al., Mander et al.). For instance the analyses carried out have shown an increase in concrete ductility when steel hardening of the hoops increases. compared For columns of square section the experimental data has been compared whit results proposed and models at present available; the proposed model shows a fitting significantly better
