Elastic compressive-flexural-torsional buckling in structural members

W.J. Raven, J. Blaauwendraad and J.N.J.A. Vamberský
Faculty of Civil Engineering and Geosciences, Delft University of Technology, the Netherlands

This article presents insight into the stability check for members loaded in a combination of compression and bending, in which - due to 2nd-order effects - also torsion occurs. A key decision in the opinion of the authors is the introduction of the stability parameter n* as the ratio of the total displacement and the 2nd-order part of displacement. They believe that this quantity can fulfill an 'alarming function' when judging the stability of structural members. An iteration procedure in a number of clearly distinct steps results into a general formula for n*, in which all necessary data concerning member properties and load cases are covered. The member safety is inspected by a unity check, which relates occurring stresses to strength requirements. Also checks on displacement limits are described. This new method for compressive-flexural-torsional buckling is applicable for all existing building materials in structural engineering as long as elasticity is involved. Essentially, the calculations can be done in a short time using a pocket calculator, without the use of other utilities. It has been deliberately chosen not to elaborate the derived formulas too far, in order to preserve a clear view on cohesion and procedure.

Key words: Building structures, structural members, stability, strength, stiffness, column buckling, flexural-torsional buckling, bending, twist