| Rectangular concrete-filled tubular (CFT) composite structures have obvious merits,suchas high strength, good ductility, better seismic behavior, and convenient construction. It isnecessary and meaningful to know the mechanical behavior, improve construction details of thekind of connections. It helps to assure the safety of the composite structures and widen the useofCFT composite structures in seismic area. Based on the experimental study of two kinds of rectangular CFT column to steel beamconnections, namely Side-Plate Welding (SPW) connection and Stiffened End Plate (SEP) connection,under the cyclic loading at the end of the beam tip, a nonlinear 3-D finite element (FE) analysisof the two kinds of connections under the cyclic loading by using the ANSYS program wasestablished. The constitution relationship of the core concrete and steel material were redefinedand inserted in the analysis process. The main work and conclusions are listed as follows: 1. The study development of steel moment frames, the CFT column and the CFT composite connections in the aspect of nonlinear analysis were briefly reviewed. 2. Three kinds of constitutive model of confined concrete under monotonic loading were compared, and the suitable model as the envelope curve of the constitutive model under cyclic loading was selected to perform the nonlinear analysis. On the other aspect, the constitutive model of steel under cyclic loading including the effects of local buckling and fracture was suggested. The reliability of the constitutive models of concrete and steel was verified by two numerical examples. 3. The nonlinear analysis of the above two kinds of rectangular CFT column to steel beam connections was conducted. The monotonic loading force-deformation curves from the numerical model agree well with envelope curves of the cyclic behavior from the low-reversed cyclic loading testing. The hysteresis loops from FE model under cyclic loading also agree well with that of the cyclic loading testing. The FE model was IIABSTRACT considered adequately to reflect the overall behaviors and the inelastic performance of these two kinds of connections, including the elastic limit load and ultimate load-carrying capacity, and can be proved to be correct. 4. The parameter study was conducted based on the correct FE model. The predicted damage phenomenon occurred at the end of beam, close to joint area, which corresponded with experimental results. From the analysis, it can be seen that the main influenced factor of the SPW connection is the thickness of sided-plate, and those of SEP connection are the diameter of bolts and the thickness of end-plate. 5. Based on the experimental study and numerical parameter analysis, the simplified calculation models for the monotonic moment-rotation constructive relationships of the two kinds of connections were suggested. The model can be used to the initial design of the practical engineering and the numerical analysis.
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