The Influence of Cross-Section Shape Changing on Work of Cold Formed Beam
The Necessity of taking into account the ability of cold-formed steel thin-walled profiles to gradually change its cross section shape proportionally to the load acting on it is considered. Free torsion constants Jt value for cold-formed profiles is justified. Underestimation of beam torsion due to ignoring of the cross-section contour deformation is assessed. The thin-walled Z and C-shaped cold formed steel sections recently are becoming more and more popular in the constructions of low-rise buildings. A characteristic feature of cold-formed thin-walled profiles in these structures is the need to consider not only the longitudinal and bending deformations, but also the deformations of torsion. Presently there are two approaches to analysis of structures of thin-walled cold-formed steel sections. One of them is based on the thin-walled beam theory designed by V.Z. Vlasov, another one is based on the super-critical load-carrying capacity theory. In the first approach the contour of the cross-section is non-deformable, in the second caseanalysis is carried out on the basis of a reduced cross-section, caused by local buckling of the compressed cross-section elements. Both approaches do not take into account the ability of cold-formed steel thin-walled profiles to change itscross section shape proportionally to the load acting on it. In this connection it is necessary to conduct theoretical and experimental studies of the cross-section deformation effect on behavior of cold-formed steel profiles.First of all,it is important to find out the range of section-length characteristics for cold-formed profiles in which the fact of not taking into account of contour deformation of the cross-section leads tothe significant, from an engineering point of view, error in the calculations. Also it is needed to estimatehowload types and connections applied on cross section influence on cross-section form changing.