Behaviors Of Axially Loaded And Eccentrically Loaded Concrete Filled Elliptical Hollow Sections

The concrete-filled steel tubular column(CFST) has been widely used in practice because of the high load bearing capacity, high-speed construction and good seismic performance. Besides of this, the elliptical CFST columns also possess low flow resistance and high flexural capacity, owing to the streamlined appearance and the presence of major and minor axes. The axially loaded and eccentrically loaded elliptical CFST columns were studied experimentally and numerially in this thesis. The main contents are as follows:1. Eigthteen axially loaded elliptical CFST stub columns, six eccentrically loaded elliptical CFST stub columns and three axially loaded elliptical hollow sections were tested. Considered parameters inculed diameter ratio, steel tube to concrete area ratio and eccentricity ratio. The test results show that the increase of diameter ratio greatly decreases the load bearing capacity, whereas the increase of stee tube to concrete area ratio considerablely enhences the bearing capacity and ductility. And the load bearing capacity decreases with the increase of load eccentricity. For elliptical CFST columns, no local buckling was observed before the applied load reached 90% of the bearing capacity. However, the hollow section buckled when the load reached 70% of the bearing capacity.2. Finite element models of axially loaded and eccentrically loaded elliptical CFST column were developed using the program ABAQUS. The key parameters of the finite element model, including the stress-strain relationship of steel tube and concrete, element types, element meshes and interactive behaviour between the steel tube and concrete, were carefully considered. The finite element model was validated against tests in this study and related tests. After that, parametric studies were carried out to identify their influences on the bearing capacity, including diameter ratio, steel tube to concrete area ratio, load eccentricity ratio etc.. The diameter ratio affects the bearing capacity noticeably, and its influence should be considered in design.3. Chinese code GB50936, Eurocode EC4 and method proposed by Kojiro were adopted to predict to the bearing capacities of the elliptical CFST columns. The predicted values were compared with test results. Good agreements can be obtained by the code GB50936. Conservative or non-conservative values were obtained by the code EC4, depending on whether the confinement effect was considered. Very non-conservative values would be obtained by the method proposed by Kojiro. For eccentrically loaded stub columns, conservative values were obtained by the code GB50936. Therefore a revised formula was proposed for predicting the bearing capacity of the eccentrically loaded elliptical CFST stub columns.