On distortion of symmetric and periodic open-section thin-walled members

•The distortional deformation modes for symmetric/periodic open cross-sections are addressed.•Symmetry through reflection/rotation and periodicity through translation/glide reflection are discussed.•Computationally efficient GBT-based procedures are given for each case.

This paper discusses aspects related to the mechanics underlying the distortion of thin-walled members with symmetric and periodic open cross-section, such as those commonly employed in cold-formed steel construction. The Generalised Beam Theory (GBT) framework is employed to determine the cross-section distortional deformation modes and obtain insight into the problem under consideration. Besides reviewing the well known case of reflectional symmetry, the implications of rotational symmetry and periodicity through translation or glide reflection are examined. For each case, computationally efficient procedures to obtain the distortional modes are provided. Several examples are presented throughout the paper, in order to enable a better grasp of the concepts and procedures addressed.