Flexural behaviour of concrete-filled steel tubes

This paper develops a mechanics model that can predict the behaviour of concrete-filled hollow structural section (HSS) beams. A form of unified theory, where a confinement factor ( ξ) was introduced [Steel Compos. Struct.—Int. J. (2001) 1(1) 51] to describe the composite action between the steel tube and filled concrete, is used in the analysis. A series of concrete-filled square and rectangular tube beam tests were carried out. The main parameters varied in the tests were the depth-to-width ratio ( β) from 1 to 2, and tube depth to wall thickness ratio from 20 to 50. The load vs. lateral deflection relationship was established for concrete-filled HSS beams both experimentally and theoretically. The predicted curves of load vs. mid-span deflection are in good agreement with the presented test results. Formulas which should be suitable for incorporation into building codes are developed for calculating the moment capacity of concrete-filled HSS beams. Comparisons are made with predicted beam capacities and flexural stiffness using the existing codes, such as AIJ-1997, BS5400-1979, EC4-1994, and LRFD-AISC-1999.