1.1. Distortional Buckling Formulae
Since GBT allows for the possibility of performing approximate buckling analyses including any number of deformation modes, one may develop analytical formulae providing accurate distortional buckling stress estimates for lipped channel, Z-section and rack-section columns, beams and beam – columns with several support conditions (Silvestre and Camotim, 2004a, b). These formulae are obtained through symbolic GBT-based bifurcation analyses that include only either one (columns) or two (beams and beam-columns) cross-section distortional deformation modes: modes 5 (symmetric) and 6 (anti-symmetric) in Figure 3, where this procedure is illustrated for the case of lipped channel members. Extensive parametric studies showed that the buckling stress estimates provided by the GBT-based formulae (i) are consistently accurate and (ii) always compare favourably with the values yielded by formulae previously developed by other authors.