Numerical analysis of concrete-filled steel tubes subjected to axial force

Proper material constitutive models for concrete-filled steel tube (CFST) are proposed and verified by the nonlinear finite element program ABAQUS against experimental data. The cross sections of the CFST in the numerical analysis are categorized into three groups, i.e., circular section, square section, and square section strengthened by reinforcing ties. Via the numerical analyses, it has been show that for circular CFST, the tubes can provide good confining effect to concrete especially when the diameter-to-tube thickness ratio is small. For square CFST, the tubes do not provide too much confining effect to concrete especially when the diameter-to-tube thickness ratio is large. The confining effect of square CFST with reinforcing ties is enhanced by the use of reinforcing ties especially when the tie spacing is small and the tie number (or tie diameter) is large.