Weak axis buckling of steel-concrete composite columns under strong axis bending

Steel concrete composite columns in the form of encased rolled steel sections are normally assumed to susceptible only to in-plane buckling, to in-plane failure under combined bending and axial load, or to cross-section failure under biaxial bending and axial load. These columns have a high torsional stiffness, so failure by lateral-torsional buckling is eliminated. This paper discusses the failure mode of weak axis buckling failure when a composite column is subjected to axial load and major axis bending alone. This failure mode does not appear to have been studied before, so this paper sets out the mechanics behind this failure mode and presents numerical predictions of column buckling in this mode. The paper concludes that most cases of lateral buckling under major axis bending can be treated by identifying a specific slenderness of column at which lateral buckling overtakes in-plane strength failure as the critical failure mode. The study is equally applicable to reinforced concrete columns, which are also susceptible to this mode of failure.