Non-uniform torsion of stiffened open thin-walled members of steel structures

A general solution is derived, from distributional differential equations of equilibrium, for thin-walled structural members that are non-uniformly torsioned continuous, or situated in a Winkler rotational-elastic medium, with constant open cross-sections, stiffened with transversal ribs along their length. The equations were solved for a general case by means of the Laplace transform. Solutions were obtained in the form of closed generalized functions, holding good — for both non-uniform torsion displacements and internal forces and their influence lines — along the entire length of the bars. The effect of ribbing (diaphragms and closed ribs) on constrained torsion displacements and internal forces and on the respective influence lines is assessed for single-span and continuous I-section structural members.The results of non-uniform torsion tests carried out on I-bars stiffened along their length with battens or closed ribs (Fig. 12), in order to verify the theoretical models of the stiffened members (particularly with battens), are discussed. The test results confirmed the poor effectiveness of stiffeners in the form of battens directly joining the flanges of I-section members (Fig. 12(a)), due to the deformation of the flanges. The deformation can easily be eliminated by modifying the battens so that they join the flanges to the web (Fig. 12(b)). Tests showed that, by using the modified battens, one can effectively stiffen open thin-walled members. The effectiveness of the stiffening that is obtained is similar to that of stiffeners in the form of closed ribs.