Physical interpretation of Wagner term in flexural-torsional buckling

Addressed herein is the Wagner term in Aexurahtorsional buckling of thin-walled axially loaded open-profile columns, which has drawn much attention following its rejection by Ojalvo in 1981 . Considered are issues related to the physical interpretation of the Wagner term, ie. absence of a free body diagram that validates the buckling equations, role of the Actitious lateral Ioad in the analysis and the single Iine representation of a column. The fundamental features of the problem are illustrated using two simple bar models. Next, a statically admissible free-body diagram for Aexurahtorsional buckling of an open-proAle column is described, without resorting to the disputed Actitious lateral load. The Wagner term is shown to be an internal stress resultant component of the longitudinal prebuckling forces distributed across the member section. It is shown that the spatial effect of stresses contributing to the Wagner term cannot be captured by the single Iine representation as proposed by Ojalvo.