The collapse of steel model columns with unequal flanges. I. Perfect

The paper is concerned with the collapse behaviour of initially straight pin-ended steel columns having unequal flanges. A modified Shanley model column with unequal flanges is presented and analysed, together with the corresponding modified Calladine construction. Each column flange is assumed to have a uniform state of stress and strain, and to behave elastically until fully yielding in compression or tension—thus local buckling is not included. However, column buckling is fully allowed for, and the complete collapse behaviour of various model column designs is investigated, the parameters varied being the normalised column slenderness, and the flange area ratio. The behaviour of the model columns is shown to agree well with that of corresponding real columns, i.e., columns of uniform cross-section that deform at all points within the volume. Compressive yield of the smaller flange is an expected source of failure, but the results show that tensile yield of the smaller flange can be equally important. Violent collapse behaviour is shown to be possible whether the smaller flange yields in compression or tension. This is particularly so at intermediate slenderness. The results apply most directly to unsymmetrical I-sections, but are also relevant to T-sections, and to wide stiffened compression panels. The Calladine construction greatly elucidates behaviour.