Stability and design of normal and high strength steel CHS beam-columns

Abstract An experimental and numerical study into the global buckling behaviour of structural steel circular hollow section (CHS) beam-columns with normal and high strength steel grades is presented in this paper. Two cold-formed S700 CHS profiles – 139.7×4 and 139.7×5 (diameter × thickness, in mm), were used in the beam-column testing programme. Ten CHS specimens were tested under eccentric compression, resulting in a combination of axial compressive force and uniform first-order bending moment. Digital image correlation (DIC) was used in the experiments to enable full-field monitoring of the strain and deformations in the specimens. Finite element (FE) modelling was also carried out with the aims of first replicating the test results and then generating further numerical data to complement the test data pool. Assessment of the existing EC3 design provisions was carried out against the test and FE data, which revealed that the lack of account taken for the full influence of varying yield strengths leads to inaccuracies in the EC3 resistance predictions. Improved design rules were proposed accordingly and shown to result in considerably more consistent predictions of buckling strength across a wide spectrum of steel grades. Lastly, a reliability assessment of both the EC3 and proposed design approaches was performed in accordance with EN 1990. The statistical results confirmed that the current EC3 partial safety factor is suitable for use with the new design proposals.