Structural performance of cold-formed high strength steel tubular columns

This paper presents a numerical investigation into the structural performance of cold-formed high strength steel tubular columns with square, rectangular and circular cross-sections. A finite element model was developed and validated against experimental results on the cold-formed high strength steel tubular columns. Parametric studies using the validated finite element model were carried out to determine the strengths of cold-formed tubular columns with various cross-sectional dimensions, member slenderness values, geometric imperfections and steel grades of S700, S900 and S1100. It was found that increasing the steel grade of the columns led to higher normalised column strengths which were less severely affected by geometric imperfections. The effect of material tensile strength to yield strength ratio on the column strengths was found to be insignificant. Based on the experimental results in literature and the results obtained from parametric studies, the applicability of the design rules in European, Australian and American Standards to cold-formed high strength steel tubular columns was evaluated. The reliability of the design rules was also assessed by performing reliability analysis. The design rules in these standards provide conservative predictions for the strengths of cold-formed high strength steel tubular columns. Recommendations on the column buckling curve selection are discussed. An improved column buckling curve expression considering the increment in normalised column strength with increasing steel grade is also proposed.