Inelastic storey-buckling factor of steel frames

Abstract

This paper first briefly reviews the modified effective length method in the literature for design of steel columns considering the inter-column interaction with the limitations outlined. To overcome these limitations, a new storey-buckling approach for steel frames is presented, where each storey is treated as a whole at the sway buckling, and its resistance is evaluated using the presented storey-buckling factor, which can be obtained from the defined storey slenderness using the relationships illustrated by the column curves in current codes. In total, 30 frame examples, considering the effects of storey number, the span number and the configuration of axial forces in columns, are adopted to examine the proposed method. Comparisons between FE results show that the presented method has good performances in predicting the failure load of considered frames. In FE analysis, the geometric and material nonlinearities as well as two types of geometric imperfections and longitudinal residual stresses are considered. Predictions from the notional load approach are also compared with FE results for some cases, which shows that these predictions may underestimate or overestimate the failure load of certain frames. The interaction between the sway buckling of the whole storey and the non-sway buckling of the weakest column may reduce the failure load of steel frames. In this study, a reduction factor is presented to consider this mode interaction, and comparisons with FE results show that this method can reasonably assess the adverse effects of this mode interaction.