Research On Basic Property Of Elliptical Concrete Filled Steel Tube

Concrete Filled Steel Tube (CFST) is a kind of composite member formed through filling concrete in steel tube. CFST structure fully combines the good performance of concrete in compression with the good property of steel in tension, it owns many advantages of high capacity, good ductility and toughness, good performance of fire resistance, superior seismic performance, simple construction method and good economic effect, so in recent years it is more and more used in various kinds of practical engineering structure. At present, cross-section shapes adopted in CFST are mainly circular, square and rectangular, research and application of elliptical concrete filled steel tube at home and abroad is relatively rare. Elliptical cross section not only meet the needs of architectural aesthetic, but also provide structural advantages associated with sections of differing major and minor axis properties. For example, under the premise of same cross-sectional area or weight, the bending capacity of elliptical concrete filled steel tube around the short axis is significantly greater than that of circular concrete filled steel tube. In addition, elliptical cross section can effectively reduce wind load that comes along the long axis of elliptical cross section. Therefore, study on basic performance of elliptical concrete filled steel tube can not only fill the vacancy of research on elliptical concrete filled steel tube at home and abroad, but also can provide guiding recommendations for practical project.The purpose of the research is to obtain relevant conclusions and provide theoretical basis for the design of elliptical concrete filled steel tube member through studying basic mechanical properties of elliptical concrete filled steel tube of different shapes of cross-section and different confinement factors; furthermore, obtaining drag coefficient of elliptical cross section under different Reynolds numbers through numerical simulation by CFD software and the formula of calculating wind load.In this thesis, a common finite element software is first used to simulate tests of circular concrete filled steel tube and compare the simulation results with the test results, verifying the feasibility of using the finite element method to analysis the basic property of concrete filled steel tube. Then, simulate elliptical concrete filled steel tube member under different force state using the same finite element method. The research content of this thesis mainly contains the following parts:1) Simulate and analysis elliptical concrete filled steel tube short column under axial compression using finite element software, study the influence of cross-section shape on the confinement effect, obtain calculation formula of composite strength of elliptical concrete filled steel tube.2) Simulate buckling of elliptical concrete filled steel tube long column around the long and short axis of elliptical cross-section using finite element method, study the influence of slenderness ratio on stability capacity, summarize stability capacity calculation formula of elliptical concrete filled steel tube long column around long and short axis based on the idea of "unified theory".3) Derive ultimate flexural capacity theoretical calculation formula of elliptical concrete filled steel tube around long and short axis adopting plastic limit equilibrium method, and verify the correctness of the formula through comparing the results of formula with the results of finite element simulation; obtain flexural capacity practical calculation formula of elliptical concrete filled steel tube around long and short axis based on the idea of "unified theory".4) Obtain the correlation curve of N/N₀～M/M₀through finite element simulation and analysis of elliptical concrete filled steel tube under eccentric compression around long axis and short axis, summarize correlation equation of of elliptical concrete filled steel tube under N/N₀～M/M₀ eccentric compression around long axis and short axis based on the idea of "unified theory". 5) Simulate elliptical cross-section flow around along long axis by CFD software, and obtain the drag coefficient of elliptical cross-section of different shapes under different Reynolds numbers, compare the drag coefficient of elliptical cross-section with that of circular cross-section indicating that elliptical cross section can effectively reduce wind load.Finally, this thesis carries out some conclusions according to the research and points out the shortcomings of the research.