Wagner term in flexural-torsional buckling of thin-walled open-profile columns

Abstract

This paper considers the Wagner term in flexural-torsional buckling of thin-walled open-profile columns, which has drawn much attention following its rejection by Ojalvo in 1981. During the ensuing debate on the subject, further issues of flexural-torsional buckling were raised highlighting the need for a comprehensive clarification. This paper collates various questions that have not been convincingly answered. In tackling these questions, two simple bar models are first used to clarify important differences between alternative representations of internal stress resultants, and their relationship with the Wagner term. With this background, a statically admissible free-body diagram is described, establishing the Wagner term without resorting to disputed means such as the use of a fictitious lateral load. The Wagner term is shown to be an internal stress resultant of the longitudinal prebuckling forces distributed across the member section; this stress resultant is of the same order of magnitude as the St Venant and warping torque. The spatial effect of stresses contributing to the Wagner term cannot be captured by the single line representation as proposed by Ojalvo.