Experimental and analytical study of square tubed concrete-encased cross-shaped steel (TCCS) columns under axial compression

Abstract

This paper presents an experimental and analytical study on square tubed concrete-encased cross-shaped steel (TCCS) columns under axial compression. The effect of test variables covering the steel section types (Type B and L), steel tube thicknesses (2.75, 5.00 and 7.50 mm) and external CFRP layers (0, 1, 2 and 4) on the mechanical behavior of the specimens were investigated. The test results show that obvious local buckling of the flange is mainly observed in the specimens embedded with Type B steel section with a larger width-thickness ratio and severe concrete crushing is also detected in the corresponding position. The constraint provided by the flange of the Type B steel section in suppressing the lateral deformation of inner concrete is weaker than that of the Type L section, leading to the inferior behavior of load capacity, ductility, and energy absorption, whereas the impact of steel section type becomes less significant to the dilation behavior of TCCS columns with sufficient confinement provided by the external tube. Furthermore, the confinement mechanism of steel section confined concrete is interpreted based on the buckling theory, and the stress–strain model of confined concrete in TCCS columns is proposed by considering the dual confinement from external tube and steel section. Finally, an analytical model is developed to predict the load–strain relationship of TCCS columns according to the section analysis method. By comparing the predictions with the experiments in this paper and several existing literature, it can be found that the proposed analytical model possesses satisfactory accuracy and applicability.