Buckling of stepped columns considering the interaction effect among columns: Fid-Bau Portal

Buckling of stepped columns considering the interaction effect among columns

Tian, Weifeng / Hao, Jiping / Zhong, Weihui

Abstract The effective length factors of stepped columns, as provided by the current design codes, are not suitable for certain situations, such as multi-bay frames and pitched-roof portal frames, because the interaction effect among the columns and the influence of the roof inclination angle are not considered. This paper proposes a simple but accurate hand calculation method to evaluate the effective length factors and second-order effects on framed stepped columns. In this approach, the expression of the negative lateral stiffness for stepped columns is first determined and then used to determine the effective length factors considering the interaction effects among columns. This is followed by a theoretical analysis to evaluate second-order effects, and expressions for calculating the deflection and moment amplification factors are developed. A practical method to account for the influence of the roof inclination angle for frames with stepped columns is also presented. The results of the performed eigenvalue and nonlinear static analyses demonstrate the validity of the proposed method. Based on the presented analysis, recommendations are made for the improvement of current design codes. Finally, the values of the key factors, α s0 and α sN, for some common cases are determined. The findings will assist in the development of reliable and cost-efficient designs of stepped columns in mill buildings.

Highlights • Evaluated effective length factor and second-order effect for framed-stepped columns. • Interaction effect among columns was considered. • Proposed approach is simple and applicable to wide range of frame types. • Proposed approach exhibits high accuracy and ease of implementation.