Nonlinear response of structures is commonly predicted from the experimentally evaluated elastoplastic material parameter dataset. This paper presents an inverse approach for the identification of plastic constitutive parameters from the response of structures obtained from the finite element method coupled with genetic algorithm. Behaviour of a slab containing centrally located fillet curved notch subjected to cyclic bending is used for the evaluation of the plastic properties and the hysteretic stress-strain curves obtained from the evaluation are in good agreement with the original curves. The approach could be used in developing constitutive relations for materials under complex 3D states of stress by judiciously designing an experimental setup involving complex shapes of structures with simple load application, which will significantly reduce the costs of generating complex 3D loading on simple shapes of specimens as traditionally followed. The material parameters obtained are more realistic as they account for the true status of the structures.