Behaviour of hexagonal concrete-encased CFST columns subjected to cyclic bending

The hexagonal concrete-encased CFST column consists of a CFST (concrete-filled steel tube) core and a hexagonal-shaped reinforced concrete (RC) encasement. This paper presents the finite element (FE) analysis of hexagonal concrete-encased CFST columns subjected to axial compressive forces and cyclic bending moments. High-fidelity finite element analysis (FEA) model is established and validated by comparison with the test data in terms of failure mode and hysteretic curves. From the FEA model, the hysteretic response of the composite columns, the contact stress between the steel tube and concrete, and the strength contribution of different components during the full range of loading are illustrated. Parametric analysis is conducted to investigate the influences of various parameters on force-displacement envelope curves of the hexagonal concrete-encased CFST columns. The parameters include the material strength, confinement factor of CFST section, stirrup characteristic value, area ratio of CFST core to RC encasement, and axial force ratio. Finally, simplified methods are proposed to predict the flexural strength of hexagonal concrete-encased CFST columns. The predictions from simplified methods showed good agreement with the experimental and analytical results.