This paper considers the cross-sectional strength behaviour of concrete filled steel box columns. The types of columns considered have very thin steel walls and have been used very recently to provide economy of construction for columns in multistorey buildings. A cross-sectional analysis method is developed which employs a rigid plastic analysis procedure to ascertain the strength interaction envelope for axial force and bending moment. This rigid plastic analysis method assumes the concrete is fully crushed, the steel has fully yielded and it also incorporates the effects of local and post-local buckling of the steel in compression regions of the column using an effective width model. A parametric study is conducted to consider the effects of varying concrete compressive strength and steel plate slenderness limits. A regression analysis is then carried out in order to determine a generalized model for the strength analysis procedure. This has enabled the development of generalized design equations useful in determining strength envelopes for design. The generalized approach is calibrated against independent test results and found to be conservative in its prediction of the strengths of the tested cross-sections.
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