Experimental Evaluation of the Warping Deformation in Thin-Walled Open Section Profiles

The analysis of thin-walled open section beams can be performed by means of Vlasov's theory of the sectorial areas. It is well-known that this type of profiles, when subjected to torsional actions, are characterised by the warping deformation and, consequently, by a further stress state whose intensity is comparable with that produced by mere flexural deformations. In the literature many papers are focused on the structural behaviour of these elements, but, to the Author's best knowledge, none proposed an experimental technique to evaluate first-hand this particular behaviour. In order to verify the classical theory of the sectorial areas, in the present paper an experiment regarding a thin-walled open section profile subjected to flexural and torsional loads is performed. With the help of a specific optical device, suitable for precision measurements, the warping displacements of a U-shaped section are easily acquired. These are compared to those derived, first, from an analytical formulation, originally devised to deal with vertical thin-walled bracings belonging to the structural core of a tall building, and, secondly, from a FE program, in which the steel profile is modelled by means of thin-shell elements. The numerical comparison confirms the reliability of the analytical formulation.