The research is focused on the investigation of the design methods of moment resisting steel framed structures (MRF) in seismic areas. The Eurocode 8, the main reference for earthquake design in Europe, allows four design approaches. Two of these (i.e. the lateral force method and the modal response spectrum), are based on linear finite element analysis, while the other methods (i.e. the pushover and the time history) are based on non-linear analysis. In the current design practice, linear analysis are preferred because they lead to a simpler structural modelling and to easy interpretation of the results. It is a common idea that Eurocode 8 should guarantee the same structural performance independently from the analysis method used. In order to state the validity of this idea it is useful to estimate with non-linear analysis the performance of an extended sample of structures designed with linear methods. In accordance to the research purpose, this paper shows and explains the preliminary results obtained analysing a single MRF.