Load-bearing capacity of concrete-filled steel columns

This paper represents the analysis of 1303 specimens of CFST experimental data. Test results are compared with EC4 provided method for determining the load-bearing capacity of these composite elements. Several types of CFSTs were tested: both circular and rectangular cross-sections with solid and hollow concrete core with axial load applied without and with moment, with sustained load and preloading. For circular cross-section columns there is a good agreement between the test failure load and the EC4 calculation for both short and long columns with and without moment. For rectangular cross-section columns the agreement is good except when the concrete cylinder strength was greater than 75 MPa, when many tests failed below the strength predicted by EC4. Preloading the steel tube before filling with concrete seems to have no effect on the strength. This paper also presents the stress distribution, confinement distribution and complete average longitudinal stress-strain curves for concrete-filled steel tubular elements. Based on the definition of the "Unified Theory", the CFST is looked upon as an entity of a new composite material. In this paper, the research achievement of the strength and stability for centrifugal-hollow and solid concrete filled steel tube are introduced. These behaviours relate to the hollowness ratio and the confining indexes of corresponding solid CFST. If the hollow ratio equals to 0,4-0,5 and over, the N-ϵ relationship exists in steady descending stage. The critical stress of CFST elements stability is determined as an eccentric member with the initial eccentricity by use of finite element method.