Research On Effective Length Of Concrete-filled Steel Tubular Frame

Concrete-filled steel tube (CFST) is a kind of composite structures which has excellentmechanical properties and construction performance. Therefore, it have been widely used inhigh-rise buildings, skyscraper and large span arch bridges. Consulting the research of someliteratures, the effective length factor of CFST frame columns can be calculated referring todesign specification for steel structure based on analytic method. So, it is demanded to give asimple useful and reasonable approach to design the CFST structure.For these reasons, the effective length of concrete-filled steel tubular columns wasanalysised based on analytic method and the finite element method. Contents are shown asfollows:(1) Through introducing the modified calculation formula of composite stiffness and theassumptions, the equation for the effective length factors of CFST columns in non-sway andsway frames can be derived using the three column assemblage model, according to the steelstructure design method.(2) A simplified finite element analysis (FEA) model of composite frame with CFSTcolumns and I-steel beam, which has considered the geometrically nonlinearity, is developedto study the effective length factor of CFST frame columns. Using ABAQUS software, thebucking critical load of the structure was obtained, based on the liner buckling analysis andthe non-linear buckling analysis. The effective length factor of CFST frame columns isobtained by making the bucking critical load into the Euler formula. The buckling analysiswas carried out by adjusting the section of beam and column, and established the differentmodes of sway frame and non-sway frame with CFST columns. The table of the CFSTcolumn effective length factor was also obtained. The effective length factor formulas ofCFST columns are derived by regression parameter using function of Matlab software. It can beused as reference for the structural design.(3) Based on the liner and no-liner buckling analysis in different stories and differentspans composite frame with CFST columns and I-steel beam, the effects of different storiesand spans to effective length of CFST columns are obtained. The influence of semi-rigid connection between beam and column are discussed based on the buckling analysis of thesimplif ied FEA model.