In this study, a simplified beam-to-column connection is presented which was specified in EC3 Annex J. The effect, at the global a nalysis stage, of having semi-rigid joints instead of rigid or pinned jo ints will be to modify not only the displacements but also the distribution of the internal forces in the structure. The mome nt and relative rotation are related through a constitutive law which depends on the joint properties. In a frame with semi-rigid joints the loading will create both a bending moment a nd a relative rotation between th e connected members. Recent limit state specifications permit the concept of semi-rigid connection of the individual frame members in the structural design. Conventionally, the anal ysis of frame structures is based on the assumption that all connections are either frictionless pinned or fully rigid. The frame el ements are constructed from a predetermined rang e of section profiles. In this paper, a genetic algorithm is pr oposed for discrete minimal we ight design of steel planar frames with semi-rigid beam-t o- column connections.