Torsional-Flexural Buckling of Thin-Walled Sections Under Eccentric Load

A detailed analysis of the behavior of thin-walled open sections under eccentric loading is presented, with emphasis on singly-symmetric sections loaded in the plane of symmetry. It is shown that for a given shape, depending on eccentricity and slenderness, a variety of behavior modes is possible: continuous purely flexural beam-column behavior, flexural instability, torsional-flexural instability and, in exceptional cases, purely torsional instability. The purpose of this paper is the development of accurate design methods and procedures. For most practically important open shapes yielding by simple flexural beam-column action governs when the load is applied on the side of the shear center opposite from that of the centroid. If the load is applied on the open side of the section, or between shear center and centroid, failure can be by torsional-flexural instability, by yielding in the beam-column mode, or by flexural instability. Experimental investigation is in very satisfactory agreement with theory.