Research On Correlation Curves Between Axial Force And Bending Moment Of CFST Laced Columns And Truss Arches

Both of concrete filled steel tubular (CFST) laced columns and truss arches are cancelled structures, compositing of smaller diameter CFST member and connection members. They have great bending rigidity and are widely used in civil engineering. However, the design calculation theory for such structures is not mature. Therefore, researches on correlation curves between axial force and bending moment of CFST laced columns and truss arches are conducted in this paper. The main research works have been carried out as follow:1) Based on the continuous assumption and conception of efficient axial compressive rigidity, a simplified FEM was proposed, in which CFST cancelled structures was stimulated as solid bar structure and the correlation buckling of the structures was taken into account. Based on this FEM, a program was edited by FORTRAN language, which improves the computation efficiency with enough precise analysis results.2) Experimental and theoretical research on correlation curves between axial force and bending moment of CFST laced columns including eccentrically tensile loads were carried out. The differences between tensile strength and compression strength of CFST member should be considered in the calculation of its correlation curves. It was pointed out that correlation curves in design criteria for CFST structure in China had a deficiency. The influences of concrete and steel strength, steel ratio and slenderness ratio on correlation curves were studied by FEM and correlation curves equation of CFST laced columns was presented. The influence of correlation buckling on ultimate load-carrying capacity of CFST laced columns was studied and a corresponding simplified calculation method was proposed.3) Taking L/4 section inner force of parabolic CFST truss arches as nominal inner force, the feature of stability factor of parabolic CFST arches was analyzed. Its critical slenderness ratio between strength failure and elastic-plastic buckling and the critical slenderness ratio between elastic-plastic buckling and elastic buckling were obtained. The expression of stability factor of CFST parabolic truss arches was divided into three parts (strength failure part, elastic-plastic buckling part and elastic buckling part) and proposed. Correlation curves equation of CFST truss arches was presented. The influence of correlation buckling on ultimate load-carrying capacity of CFST truss arches was studied and a corresponding simplified calculation method was proposed.4) Based on the stability factor of CFST laced columns and the relationship between gyration radius and section height by statistics, the safe shear formula of CFST laced columns was proposed. The calculation method for the inner force of the web member in the truss arches was presented. The stability analysis method in CFST laced columns considering the shearing flexibility factor of the laced members was adopted in predicting the ultimate load-carrying capacity of CFST truss arches, and a corresponding calculation method was gained.