Before revision:  In case of nonassociative plasticity, a modified Davis approach is used . The optimization problem is analyzed and the corresponding duality between the static and kinematic principles  is derived.
After revision:  In case of nonassociative plasticity, a modified Davis approach were used for approximation of the standard SSR method. The OPT-SSR method computes the factor of safety without performing an elasto-plastic analysis, similarly as in limit analysis. It is shown that this optimization problem is analyzed and the corresponding duality between the static and kinematic principles is derived.