WAGNER TERM IN FLEXURAL-TORSIONAL BUCKLING OF THIN-WALLED OPEN-PROFILE COLUMNS

This paper considers the Wagner term in flexural-torsional buckling of thin-walled open-profile columns, which has drawn much attention foll owing its rejection by Ojalvo in 1981. During the ensuing debate on th e subject, further issues of flexural-torsional buckling were raised h ighlighting the need for a comprehensive clarification. This paper col lates various questions that have not been convincingly answered. In t ackling these questions, two sim pie bar models are first used to clar ify important differences between alternative representations of inter nal stress resultants, and their relationship with the Wagner term. Wi th this background, a statically admissible free-body diagram is descr ibed, establishing the Wagner term without resorting to disputed means such as the use of a fictitious lateral load. The Wagner term is show n to be an internal stress resultant of the longitudinal prebuckling f orces distributed across the member section; this stress resultant is of the same order of magnitude as the St Venant and warping torque. Th e spatial effect of stresses contributing to the Wagner term cannot be captured by the single line representation as proposed by Ojalvo.