Evaluation of the ductility features in steel structures with softening moment-rotation behaviour based on a nonconvex optimization formulation

In order to determine the ductility features of steel structures, several a pproaches have been introduced in the bibliography. In this paper a certain method is proposed which considers the actual form of the moment-rotation curve, including the possible softening branches. Moreover, stability pheno mena are also taken into account as they significantly influence the overal l response of the structure. For the effective application of the considere d method, a solution algorithm was developed, mainly based on the nonconvex optimization theory. The numerical applications that follow demonstrate th e applicability of the adopted approach.