The behaviour of T-section beam-columns is studied; a numerical study and comparisons with current design rules are presented. Definitions of appropriate buckling reduction factors for local and global torsional and lateral-torsional buckling modes are discussed. The centroid shift in the effective section approach and the cross-sectional classification for the Eurocode rules for beam-columns are analysed. A proposal for a simplification and improvement of the EC3 rules is made.