On The Restrained Torsion Of Thin-Walled Beams

The following several aspects of research on the restrained torsion of thin-walled beams are discussed in this paper:1.While using FEM to compute the restrained torsion of thin-walled beams, the problem of which are the best equivalents of torsional moments loaded to the opened cross section and closed cross section thin-walled beams are discussed in the paper. A new point is put forward that transverse bimoment has different influence on the two kinds of cross section thin-walled beams, and on their St-Venant principle conditions.2.According to the fact that transverse bimoment has serious influence on the warping displacement and the warping stress of closed cross section thin-walled beams, the dissertation researches on the warping stress caused by transverse bimoment, and presents a maximum warping stress calculating formula to the transverse bimoment for box-shaped thin-walled beams for the first time.3.Studying on Vlasov theory about the restrained torsion of opened cross section thin-walled beams and on Wumansji theory about the restrained torsion of closed cross section thin-walled beams, the paper points out the advantages and the disadvantages of the displacement modes about Vlasov theory, analyses the internal cause to high error of Wumansji theory. Some suggestions are proposed to establish a more accurate restrained torsion theory.4.From the point of engineering application, a modification formula is established to modify the maximum stress for Wumansji theory in the paper. The validity and the practicability of the modification formula are validated by lots of classic examples.5.A new restrained torsion theory about closed cross section thin-walled beams is developed based on the Wumansji theory. The effect of the profile deformation is considered indirectly by introducing a modification-warping coefficient, and the shear of St-Venant is taken into account in the new theory. The result of examples indicates that the new theory has a higher computational accuracy than Wumansji theory, yet retains the traits of simplicity and practicability of Wumansji theory.6.Put doubt on the broad sense method according to its establishment of the differential equations.