The behaviour of self-consolidating concrete (SCC) filled hollow structural steel (HSS) stub columns subjected to an axial load was investigated experimentally. A total of 50 specimens were tested. The main parameters varied in the tests are: (1) sectional types: circular and square; (2) steel yielding strength: from 282 to 404 MPa; and (3) tube diameter or width to wall thickness ratio (D/tor B/t): from 30 to 134. A mechanics model is developed in this paper for concrete-filled HSS stub columns. A unified theory is described whereby a confinement factor (ξ) is introduced to describe the composite action of the steel tube and the filled concrete. The predicted load versus deformation relationship was in good agreement with test results. The theoretical model was used to investigate the influence of important parameters that determine the ultimate strength of the composite columns. The parametric and experimental studies provide information for the development of formulae for the calculation of the ultimate strength and the axial load versus axial strain curves of the composite columns. Comparisons are made with predicted stub column strengths using the existing codes, such as ACI-1999, AISC-LRFD-1999, AIJ-1997, BS5400-1979 and EC4-1994.

Concrete-filled steel CHS (circular hollow section) columns are currently being increasingly used in the construction of buildings. Limited information is available on the models for the moment (M) versus curvature (φ) response, and the lateral load (P) versus lateral displacement (∆) relationship of these columns subjected to axial load and cyclically increasing flexural loading. Eight concrete-filled steel CHS specimens were tested under constant axial load and cyclically increasing flexural loading. The parameters in the study included the concrete strength (fcu) and the axial load level (n). A mechanics model is developed in this paper for concrete-filled steel CHS columns subjected to constant axial load and cyclically increasing flexural loading. The predicted cyclic responses for the composite columns are in good agreement with test results. Based on the theoretical model, parametric analysis was performed on the behaviours of the moment (M) versus curvature (φ) response, and the lateral load (P) versus lateral displacement (∆) relationship, as well as the ductility coefficient (µ) for the composite columns. Finally, simplified models for the moment (M) versus curvature (φ) response, and the lateral load (P) versus lateral displacement (∆) relationship are suggested. A formula for the calculation of the ductility coefficient (µ) of the composite columns under constant axial load and cyclically increasing flexural loading is developed.

This paper describes a series of new compression and bending tests carried out on concrete filled steel tubes (CFST) after exposure to the ISO-834 standard fire. A theoretical model that has been previously developed is used to predict the post-fire load versus deformation relationships of CFST stub columns and beams. The predicted curves of load versus deformation are in good agreement with the new test results. The previously developed theoretical model had been used to investigate the influence of a number of important parameters on the residual ultimate strength and flexural stiffness of the composite sections and the results of the parametric studies were used to develop formulas for calculating the composite section residual ultimate strength under axial compression or flexural bending and the composite section residual flexural bending stiffness. In these formulas, the ambient temperature compression resistance, bending moment capacity and initial flexural bending stiffness of the composite section should be calculated using an existing design code. In this paper, these formulas are applied to the new test data to assess the suitability of using several different design codes: AIJ-1997, AISC-LRFD-1999, BS5400-1979, DBJ13-51-2003 and EC4-1994.

The strength and seismic behavior of a composite column may be used to assess the potential damage caused by fire and help to establish an approach to calculate the structural fire protection for minimum postfire repair. This paper provides new test data pertaining to the seismic behavior of concrete-filled hollow structural steel (HSS) columns after exposure to fire. The test parameters included the sectional types, the fire duration time and the axial load level snd. Thirteen concrete-filled HSS column specimens, including seven specimens with circular sections and six specimens with square sections were tested under constant axial load and cyclically increasing flexural loading. Comparisons are made with predicted column strengths and flexural stiffness using the existing codes. It was found that concrete-filled HSS columns after exposure to fire exhibit very high levels of energy dissipation and ductility. Generally, the energy dissipation ability of the columns with circular sections was much higher than those of the specimens with square sections. The work in this paper provides a basis for further theoretical study on the seismic behavior of concrete-filled HSS columns after exposure to fire.

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 (n) 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 (b) 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.