Limitation of Simplified Hypotheses for the Prediction of Torsional Oscillations for Thin-Walled Beams

The study of uniform torsion of thin walled beams is done fairly easily in the thin wall beam case, the effects of thickness being neglected. Then, the classical Saint-Venant warping function simplifies to the double sectorial area. The dynamical case needs the use of a more refined theory involving nonuniform warping, and characterized by supplementary dynamic torsion constants. The computed values obtained from BIEM for those constants are compared with those deduced from thin walled beam theory, and from the measurements of experimental natural frequencies. It is shown that the relative thickness acts significantly on the results in both static and dynamic torsion cases.