The contribution of CFRP (carbon fiber-reinforced polymer) to concrete-filled square steel tube (CFSST) is considered in this paper. Based on the experimental study of six high strength concrete-filled square steel tubular stub columns with inner CFRP circular tube (HCFSST-CFRP), the finite element software ABAQUS is employed to analyze the mechanical behaviors of HCFSST-CFRP stub column under axial compression load. Mechanism of interactions among steel tube, concrete core (includes two parts:

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... innermost concrete and sandwich concrete) and CFRP is analyzed, and a simplified equation of loads shared by innermost concrete and sandwich concrete is given by regression analysis. Longitudinal stress distribution in the concrete section, load shared coefficient and axial load-strain relationships are presented. The confinement effect of the CFRP tube increases ductility of HCFSST stub columns remarkably. Innermost concrete suffers most of axial load after specimen reaching ultimate bearing capacity because of the confinement effect of CFRP tube. CFRP tube begins to work obviously at the descent stage after stub column reached ultimate bearing capacity.