Effective bending stiffness of steel-concrete composite columns with multiple encased steel profiles

For the structural analysis of steel-concrete composite columns, Eurocode 4 allows only cross-sections with one implemented steel profile and double symmetry. However, there are worldwide more and more examples of composite columns with more than one embedded steel profiles, like for example in the International Financial Center of Hong Kong and the Ping Anh Finance Center in Shenzhen. The common practice of analysis of such columns is to use the simple Euler-Bernoulli beam theory to describe the global behaviour. But recently, performed tests reveal that the resulting deformations exceed largely the deformations predicted by the aforementioned analytical model. The presented contribution shows a modified approach to analyse the stiffness of composite columns with multiple encased steel profiles. Based on the performed laboratory tests and numerical simulations with the finite element code Abaqus®, a new method to determine the effective stiffness is proposed. It combines a modified Timoshenko beam theory with embedded Vierendeel truss model – the VTBM model. This modified method leads to a reduced value of the effective stiffness, more realistic deformations at Ultimate Limit State and thus to a more realistic assessment of the Euler's critical buckling load. •Columns used in high-rise buildings are often out of the scope of design codes.•Separated steel cores in a column's cross-section leads to an innovative hypothesis.•Transition from the Euler-Bernoulli beam theory towards Vierendeel truss behaviour.•Vierendeel-like beam behaviour confirmed in tests and finite element simulations.•Proposed novel analytical model allows for a more accurate stability analysis.