Numerical investigation on compressive performance of CFST columns with encased built-up lattice-angles

This paper presents a numerical investigation on the compressive behaviour of thin-walled concrete-filled steel tube (CFST) columns with encased built-up latticed angles. The additional confinement provided by encased angles was considered in the finite element (FE) model, in addition to the contact between tube wall and inner concrete and the effect of tube-wall confinement on concrete model. The established FE model is verified against the existing test results that it can well predict the behaviour of reinforced composite columns under axial compression. The composite action between encased angles and concrete and the efficiency of built-up angle configurations on performance improvement are extensively analyzed through the validated FE models. The influence of three parameters, namely confinement factor (ξ), reinforcement ratio (ρsr) and slenderness ratio (λ), to the angle-contributions on lateral confining pressure and the ultimate strength are evaluated and quantified. It is found the relationship between the strengths of CFST columns and built-up member can be defined as an exponential equation. Finally the design equation based on AISC 360-10 design provisions with consideration of angle-contributions is proposed, and the comparison results show it has a desirable accuracy and satisfactory correlation with both experimental and numerical results.