Cold-formed steel elliptical hollow section stub columns under combined compression and biaxial bending

The paper presents a numerical study on the cross-section behavior of cold-formed (CF) steel elliptical hollow sections (EHS) under combined compression and biaxial bending. In the present study, a finite element (FE) model for CF steel tubular stub columns under combined compression and biaxial bending was first developed, in which the local geometric imperfections, residual stresses and enhanced material behavior were predicted by a rigorous numerical simulation of roll forming. The developed FE model for CF steel tubular stub columns under combined compression and biaxial bending was validated against test results of various tubular sections (including EHS). Then, the validated FE model was employed to carry out a parametric study for CF steel EHS with a large range of steel grades (including both high strength and normal grade steels), section sizes, loading eccentricities and angles. Based on the generated FE data, the traditional design specifications for doubly symmetric cross-sections under combined loading in EN 1993-1-1: 2005 (CEN, 2005) and ANSI/AISC 360-16 (AISC, 2016), as well as the current design equations for hot-finished (HF) normal grade steel EHS suggested by Gardner et al. (2011) under combined loading were evaluated for the design of CF steel EHS under combined loading. New slenderness limits of Class 2 and Class 3 sections, as well as new design equations of cross-section resistances, for CF steel EHS stub columns under combined compression and biaxial bending are proposed.