| Steel-reinforced concrete filled tube(SRCFT) columns formed by inserting structural steel into concrete-filled steel tubes, is a new type of modern composite column. This type of composite columns has the advantages of both steel-reinforced concrete(SRC) columns and concrete filled tube(CFT) columns, and it can adapt to the development of modern structures toward big-span, heavy-load, high-rise, extremely condition bearing and the need of industrialized production and construction. In this dissertation, based on previous research achievements of steel-concrete composite columns, the mechanical properties and design method of axially loaded steel-reinforced high-performance concrete filled steel tubular(SRCFT)columns has been extensively investigated both theoretically and experimentally. The main contents are as follows:1. Confinement coefficient, structural steel index and slenderness ratio were chosen as the main varies parameters, experimental studies on the behaviours of SRCFT columns under axially compression were carried out, including 9 stub columns and 11 slender columns. Macroscopical deformation characteristics, failure mechanism and failure modes of this new type of composite columns were observed and studied. Influence of thickness of steel tube, area of cross-section of structural steel, concrete strength grade and slenderness ratio on the ultimate bearing capacity of the composite columns were investigated. The differences between SRCFT column and CFT column were compared, as well as differences between SRCFT columns under hinge support condition and plate support condition.2. The peeling method was set up and employed to analyze SRCFT stub columns.σ-εlcurves of structural steel, steel tube and core concrete, and distribution relationships of axial force between structural steel, steel tube and core concrete were derived by assuming steel in 2-dimensional stress state. The above analysis separated the load sustained by structural steel, steel tube and core concrete, which in turn intensify the understanding and knowledge about the interaction of structural steel, steel tube and core concrete, and working mechanism of SRCFT stub columns.3. The nonlinear finite element analysis(FEA) of SRCFT stub columns under plate support loading condition was carried out using ANSYS program, and the calculated curves were in good agreement with test curves. Based on analysis of vertical stress and equivalent stress distributions of core concrete in different load stages when the columns entered elastic-plastic stage, the confining mechanism between structural steel, steel tube and core concrete was investigated.4. Cross-section strength formulas of SRCFT stub columns have been derived by using superposition principle and limit equilibrium theory. Based on the test results, the practical formula to calculatet the ultimate bearing capacity of the composite columns was established by introducing stiffening coefficient. Finally, the calculation results of different formulas for calculating the ultimate bearing capacity of the composite columns were comparatively analyzed.5.Based on the stability theory and tangent modulus theory, the formulas for calculating the ultimate bearing capacity and the bounds slenderness ratio of elastic and elastoplasticity stability of axially loaded SRCFT slender columns were obtained. According to the working mechanism and stress characters of core concrete of the composite column, a core concrete stress-strain relationship based on Saenz model was put forward, by considering of confining contribution of steel flanges. Full-range load-deformation relationship for the composite slender columns under axial load was calculated by using fiber element approach, and parametric studies were conducted to examine the influencing factors of the stability coeffcient of the composite slender columns. A simplified formula for calculating ultimate bearing capacity of the composite slender columns was obtained. At last, the calculation results of different formulas for the composite slender columns were comparatively analyzed.6. The expressions for statistic parameters of integrated resistances of axially loaded SRCFT columns were deduced by using mathematical analysis method, and reliability analysis was completed using JC method. The influences of different load combinations, specific values of loads, strength grades of concrete, thickness of steel tube, area of cross-section of structural steel, steel yield strength and slenderness ratio on the reliability index of the composite column were studied.
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