Improving the GBT-based buckling analysis of restrained cold-formed steel members by considering constrained deformation modes

This paper reports the development, numerical implementation and practical application of a novel/improved approach to perform the buckling analysis of braced/restrained cold-formed steel members by means of Generalised Beam Theory (GBT). The novelty consists of a cross-section analysis procedure that incorporates elastic restraints and, therefore, leads to a set of constrained deformation modes with clear structural meaning for the member under consideration. The potential of the developed GBT-based approach is illustrated by presenting and discussing numerical results concerning cold-formed steel (i) purlins restrained by sheeting and (ii) studs braced by sheathing. For validation and assessment purposes, several GBT-based results are compared with values provided by the programs GBTul2.0 (conventional GBT), CUFSM (finite strip method) and/or ANSYS (shell finite elements). It is shown that the proposed GBT-based approach is much more efficient than the conventional one, as it offers the possibility of obtaining accurate buckling results with very few (constrained) deformation modes - this feature makes it possible to derive semi-analytical formulae to calculate critical buckling loadings of braced/restrained members. This capability is used in this work to derive GBT-based semi-analytical formulae providing critical length and buckling loading estimates for cold-formed steel purlins and studs restrained by panels (sheeting or sheathing).