Resistance of circular concrete-filled tubular sections to combined axial compression and bending

This paper describes strength formulae and simplified strength interaction curves for the direct strength method (DSM) for circular concrete-filled tubular (CFT) sections. A simple axial strength formula and a flexural strength formula for circular CFT sections are proposed to account for the post-local buckling strength of the circular steel skin and the increase in concrete compressive strength caused by confinement of the steel skin. The squash load predicted by the proposed strength formula is compared with test results in the literature, and those predicted by AISC specifications and Eurocode4. A simplified strength interaction curve for circular CFT members under combined axial compression and bending is proposed and compared with test results. The comparison confirms that the proposed axial and flexural strength formulae and simplified strength interaction curves can be used to conservatively predict the resistance of circular CFT columns to an axial load, and combined axial compression and bending.