Structural Beams in Torsion

Results of a study of the torsional properties of standard structural steel beams are offered for discussion in this paper. The purpose of the investigation was to furnish a reliable basis for the design of structural members subjected to torsional loads. The relation between torque and stress on the one hand, and between torque and twist on the other, for any piece subjected to torsion involves a constant the value of which is a function of the material and the shape of the cross-section. An accurate method is given for the evaluation of this torsion constant, K, for standard H-sections and I-sections, taking full account of all factors involved. This has been made possible by applying the “membrane analogy” to about sixty sections of widely varying flange, web, and fillet proportions.

The investigation included a study of the effect of end fixity in torsional design, and shows how it may be obtained effectively. The proposed formulas are applied to practical design problems, and are checked by torsional tests on structural steel sections ranging in size from a 3-in. I-beam weighing 7.5 lb per ft, to a 12 by 12-in. beam weighing 190 lb per ft.