A unified approach for austenitic and ferritic stainless steel CHS beam–columns subjected to eccentric loading

This paper develops a unified approach for assessing structural behaviour of austenitic and ferritic stainless steel circular hollow section (CHS) beam–columns​ under eccentric loading. This approach is based on combining a deformation-based method and collapse theory for stainless steel CHS beam–columns.A normalised M–N–Φ relationship of stainless steel CHS was derived based on a fibre model; the approach incorporated deformation capacity and strain hardening based on continuous strength method (CSM). The novelty of this paper is to present a closed-form solution for generating axial-load–end-moment interaction curves of the stainless steel CHS beam–column by combining the normalised M–N–Φ equation with a general beam–column equation. Besides, a critical normalised mid-height curvature was determined, which could be used to differentiate cross-section local buckling failure from global stability failure of stainless steel CHS beam–columns under combined loading. The proposed approach related the strengths of beam–columns to the effective column lengths by introducing a new non-dimensional slenderness ratio for stainless steel CHS beam–columns. It also provided an explicit way to consider the effect of column imperfections on the strengths of stainless steel CHS beam–columns. Accuracy of the derived normalised interaction curves was assessed by comparing the predictions against the test and numerical results for a wide range of non-dimensional slenderness ratios and different classes of CHS cross-sections for both stainless steel grades. A high level of accuracy and consistency was achieved in predicting the strengths of both short and long stainless steel CHS beam–columns for both types of steel grade.