LAUSR

Abstract The effective length factors of stepped columns, as provided by current design codes, neglect the interaction effect among the columns. Considerable inaccuracies could be introduced because this effect can be significant for stepped columns. This study aimed to reveal the mechanism of the interaction effect among sway-permitted stepped columns and develop a practical approach to consider this effect. Stiffness matrices were first obtained for three- and two-segment stepped columns using the slope-deflection method, and equations for lateral stiffness were developed. Next, we analysed the effect of compressive loads on the lateral stiffness of the columns. The results showed that the relationship between the normalised column stiffness and axial load could approximately be described as a broken line and the second-order effect produced by the applied axial compressive loads could be regarded as a ‘negative stiffness’. Based on these findings, equations were developed to calculate the effective length factors of three- and two-segment stepped columns considering the interaction effects among them. Examples derived from practical projects demonstrated the validity of the proposed approach.