Behaviour and design of ultra-high-strength CFST members subjected to compression and bending

Abstract

A comprehensive experimental and numerical study on the axial and flexural behaviour of square concrete-filled steel tubular (CFST) members incorporating S960 ultra-high-strength steels and high-strength concrete (C70 and C100) is reported in the present paper. An experimental programme that consisted of eighteen stub and slender CFST members under various loading conditions was conducted. The test results showed that the nominal compressive and flexural strength of ultra-high-strength CFST members were achieved. Steel coupon tests, concrete compressive strength tests and geometric imperfection measurements were also carried out. In addition, numerical models which accounted for geometric imperfections and residual stresses were developed. A confined concrete model was employed in the numerical analysis to simulate concrete confinement effects. Validation against the experimental results demonstrated the accuracy and reliability of the developed model. A series of parametric studies were performed to evaluate the effects on the ultimate strength by changing the steel yield strength, concrete compressive strength, steel tube width-to-thickness ratio and member slenderness ratios for different loading conditions. Comparisons of the results were made with the current codes of practice including AS/NZS 2327, Eurocode 4 and ANSI/AISC 360, which indicated that all the provisions were conservative in predicting the axial and flexural resistance of CFST members with recommended curves.