Behaviour and design of high strength CFST columns with slender sections

The behaviour of high strength concrete-filled steel tube (CFST) columns with slender sections under concentric loading is experimentally explored in this study. The test program includes a series of six CFST columns made of welded built-up square tube with very high strength materials and different width-to-thickness ratios. The performance of these specimens is evaluated under compression based on their failure mode, ultimate strength, strain development and axial load-shortening relationship. Moreover, a numerical model is developed considering the influence of initial local imperfections, residual stress of the steel tube and material models are proposed for composite columns. The finite element model (FEM) is verified using the experimental results and is shown to provide good predictions of the mechanical properties of CFST. Then the FEM is used to investigate the equation of AS/NZS 2327 code and propose a modified form factor for predicting the loading capacity of square CFST columns under axial compression. A database of 185 test samples is compiled with a wide range of concrete grade and section slenderness to evaluate the accuracy of the newly proposed form factor equation. Furthermore, the study also examines the optimized section of CFST columns in terms of performance and cost savings. •An experimental study of short CFST columns with slender sections and high strength materials was presented.•An accurate numerical model was also developed for a parametric study.•A new form factor of the AS/NZS 2327 design equation was proposed.•An optimized section was also proposed for high strength CFST columns.