Three-Dimensional Nonlinear Finite Element Analysis And Study On Design Theory Of Concrete-Filled Steel Tube Frames

Concrete-filled steel tubular columns are becoming increasingly popular inhigh-rise buildings because of their excellent structural advantages. However, muchof the research on CFRT (concrete-filled steel tube) to date has focused on thebehaviors of single column and connections. In contrast, relatively few researchershave investigated theoretically and experimentally the performance of the wholecomposite frames that consist of concrete-filled rectangular tube columns and steelI-girders. The design method of these structures is not mature, either. Therefore, it isnecessary to make further researches on the finite element model and design method.The seismic performance of CFRT frames was studied by the finite elementmethod and the low-reversed cyclic loading experiment. A 3-D nonlinear finiteelement model was developed in the paper, and the stress-strain relations of steel andconcrete under complex stress conditions were suggested. In the model, the effect ofthe bond between steel tube and concrete was considered, and the weld fracturesbetween steel girders and CFRT columns were simulated too. The seismic behavior ofthe CFRT frame was studied by means of the finite model and the cyclic loadingexperiment. Furthermore, an accurate and simple calculation method on the lateraldisplacement of frames was proposed in the paper.It is concluded that: (1) The 3-D nonlinear finite element model developed in thepaper can ensure high accuracy and it is recommended for conducting structureanalysis of concrete-filled rectangular tubular frames. (2) CFRT frames showfavorable seismic performance from both experimental results and theoreticalanalysis. (3) The calculation method on the lateral displacement of frames proposedin the paper is accurate and simple.