Modified beam elements - an efficient alternative to plate finite elements for modelling the behaviour of thin-walled steel structures

In the current steel constructions, the use of thin-walled members has become an everyday reality, through the use of welded profiles on one side and cold-formed profiles on the other side. This tendency leads the engineers, even for structural elements having a beam aspect, to account for a wide range of phenomena, neglected in the traditional steel constructions, and associated with the deformability of the cross sections of the used profiles. So phenomena such as local buckling, distortional buckling, lateral buckling of the flanges, or torsion resistance by distortion of the profile cannot be ignored anymore. In this perspective, the present paper presents some theoretical bases for the development of a special plane beam element allowing to account for the cross section deformability. The main idea consists in adding a complementary local displacement field, describing the cross section deformation, on a classical beam element, for which the section is assumed to be rigid. Some results are then presented, for both critical and non linear behaviour.