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Application of concrete-filled steel tubes (CFST) is becoming increasingly prominent in the civil engineering practice. However, the interaction of cross-sectional elements in CFST columns raises a number of questions, which have to be investigated in detail to improve design background and analytical resistance formulae. The aim of the current paper is to examine the structural behaviour of innovative concrete-filled steel tubes using different structural steel grades (S355, S500 and S960) and concrete classes (C30/37 and C60/75). Combination of normal or high strength steel with normal or high-performance concrete is a novel research topic of composite structures resulting in economic and optimal design for distinct civil engineering applications such as buildings, bridges, towers and masts, etc. An advanced finite element model is developed and validated based on previous experimental results found in the international literature in order to investigate the discrepancies in structural behaviour, load-bearing capacity and failure mode of stub columns subjected to pure compression. Validated numerical results are compared to formulae-based resistances and the applicability of standardised design methods are examined. In addition, a novel formula is proposed considering hardening of steel material in accordance with EN 1993-1-5. The developed formula can be used for the economic design of CFST stub columns, combining normal and high strength materials, where elastic shell buckling cannot occur (D/t ≤ 90ε2).

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