EC8-compliant steel moment resisting frames (MRFs) are often overdesigned owing to the severe requirements for lateral deformability and P-Delta effects. This is not the case of MRFs designed in accordance with North American codes (e.g. ASCE7), which require different rules to consider the structural sensitivity to the P-Delta effects. In lines with the latter approach, the current draft version of the amended EN1998-1-1 introduces a different methodology to account to the structural lateral displacements. This work aims to investigate, by both static and dynamic non-linear analysis, the effectiveness of new rules as respect to the former version of EC8 and the current ASCE7. Both non-linear static and dynamic analyses have been carried out by accounting for the real dimension of beam-to-column joints and their behaviour, which was simulated by means of a non-linear spring properly calibrated against experimental tests. The results show that the structures designed according to the latest draft version of the EN1998-1-1 and those compliant with the North American code have a similar behaviour.