The aim of the research is to determine by means of laboratory tests and numerical simulation the mechanical properties of steel that are needed for the development and ductile behaviour of highly deformed plastic zones in structural elements subjected to flexion. The objective is to supply the scientific basis for specifications of the mechanical properties of the steels grades used in steel structures, which can be calculated by methods allowing for elasto-plastic behaviour. These specifications should be suitable for inclusion in steel construction codes, in particular Eurocode 3, without causing major delays in its introduction.