Research on special-shaped concrete-filled steel tubular columns under axial compression

Six L-shaped and twelve T-shaped concrete-filled steel tubular (CFST) stub columns subjected to axial compression were experimented in this paper. The L-shaped CFST stub columns were welded vertical stiffener at the concave corner. The T-shaped CFST stub columns were stiffened by steel plate stiffeners. During the test, the experimental phenomenon and failure mode of special-shaped CFST stub columns were observed. According to axial load-displacement curves, mechanical properties such as stiffness, bearing capacity and ductility were compared and analyzed. According to the load-strain curves and load-stress curves, strain and stress development of steel tubes and constraint effect for concrete provided by steel tubes were studied. The test results show that the stiffeners can effectively delay the local buckling of steel tubes, increase the buckling capacity, and increase the constraint effect for concrete. The cross-sectional dimension of specimens has no obvious effect on the ductility and the failure modes of T-shaped CFST stub column due to the restriction of steel plate stiffener, while obviously affects the stiffness and the bearing capacity. Finite element (FE) software ABAQUS was used to analyze special-shaped CFST columns subjected to axial compression and the simulated results were in good agreement with the experimental results. Further parameter analysis with ABAQUS was carried out to study the influences of the steel ratio α, steel yield strength fy, concrete strength fck and slenderness ratio λ. Based on the experimental results and FE analysis, design formulae for calculating sectional bearing capacity and stability bearing capacity of special-shaped CFST columns are proposed.