Nowadays, moment-resisting steel frames are one of the most attractive typologies of structural systems resisting to earthquakes. According to the Eurocode for seismic design (EC8) four alternatives can be used, that differ in the type of seismic analysis and for the verification approaches. A research project is in progress at the Politecnico di Milano on the investigation of these seismic design methods. At first, this paper briefly discusses these approaches. Then attention is focused on a case-study, a one-bay four-stories rigid frame for which nine different seismic inputs have been defined. For each of them, the four admitted methods of seismic analysis are applied. The research outcomes underline nonnegligible differences from a structural point of view, suggesting the need of a deeper investigation of the range of applicability of the single methods.
