Fundamental Study On Design Theory For Centrifuge Concrete Filled Steel Tubular Structure

Centrifuge concrete-filled steel tube (CCFT) is a special kind of composite structure. It is made of a thin-wall steel tube and a centrifugal concrete tube inside. Because of its advantages, such as good elasticity and plasticity, good rigidity and small weight, it has been widely used in power engineering field and so on. In order to further apply centrifuge concrete-filled steel tube structure to other engineering fields, the development of fundamental study on design theory for CCFT structure will have significant effects on the new subject.In this dissertation, on the base of studies on constitutive relationships of CCFT structure and bond-slip, a elastic-plasticity finite element model is presented to perform three-dimensional analysis of CCFT. Modification is proposed on the design equations of ultimate bearing capacity of CCFT under single load. Mathematical expressions of ultimate bearing capacity for CCFT are inferred based on test date and theoretical analysis under complex loads, exposure to fire and after exposure to fire. The formation, working mechanism, performance, merit and demerit of several CCFT joints are introduced and several design suggestions are presented. The major contents are summarized as follows:(1) An analytical model for the constitutive relationship of CCFT was proposed by simplifying CCFT as a kind of composite material and using strain energy principle, based on existing constitutive relationship of composite structures. Examples were used to validate the analysis model and determine the effects of changing strength of the materials and steel ratio on the coefficients.(2) On the experimental researches for bond-slip performance between steel and concrete in composite structures, the mechanics of the bond between tube and centrifuge concrete in CCFT structures is analyzed in detail, based on which bond strength between tube and centrifuge concrete in CCFT structures is theoretically derived. A calculation model of bond strength and ultimate load of bond fracture is established by using the Tepfers mechanical model of thick-wall cylinder subjected to the internal pressure. Examples are provided to validate the bond strength analysis method and discussed the effects of bong strength caused by steel ratio, concretestrength levels and microscopic deviation. All these may contribute to the further analysis of performance of bond relation between tube and centrifuge concrete in CCFT structures.(3) The distribution of the bond stress between steel tube and concrete in CCFT Structures was analyzed in detail, based on which a function was assumed to represent the bond stress distribution on steel tube and concrete interface in CCFT. Differential equation of bond and slip was established by using equilibrium of horizontal forces, constitutive relationship of steel and concrete, and relations of between slip and strain of steel tube and concrete. And mathematical models about relations of boundary- size and slip, boundary- size and stress and bond-slip constitutive were established. The influence of several parameters, such as steel ratio, slenderness ratio and the cracking response of concrete, was analyzed.(4) An elastic-plasticity finite element model is presented to perform three-dimensional analysis of CCFT subjected to simple loading based on slip-deformation of the steel and concrete composite structure. This model accounts comprehensively for all significant geometric nonlinearity exhibited by CCFT, and the steel and centrifuge concrete constitutive model account for the significant inelastic phenomena. In addition, the finite element model accounts for slip between the steel and centrifuge concrete components of the CCFT by incorporation of a nonlinear slip interface. The stress-strain and load-displacement full curves of the composite construction, steel and centrifuge concrete are obtained. The finite element model is verified against experiments of CCFT members and the simplify formulations from preliminary studies under simple loading.(5)...