Study On The Seismic Behavior Of Concrete-Filled Square Steel Tube Column To Concrete-Filled U-Shaped Steel Beam Joints

The concrete-filled U-shaped steel composite beams have broad application prospects due to its high bearing capacity,good local stability,excellent fire resistance,convenient construction and high degree of assembly.For promoting the development of the composite beams,the seismic performance of two kinds of proposed square concretefilled steel tubular(CFST)column-concrete-filled U-shaped steel beam joints were studied,which were both throughout assembly.The main study work and achievements were summarized as follows:Based on the existing codes and literatures,the design method of CFST column and the full plastic section bearing capacity of the concrete-filled U-shaped steel composite beams were statistically arranged.According to the methods,three CFST columnconcrete-filled U-shaped steel beam joints with slab were designed for the two type construction methods,which were tested under cyclic load or monotonic load.The test parameters were axial compression ratio,loading methods and beam end details.Through the hysteresis curves and related strain values obtained by the tests,the paper researched the skeleton curves,bearing capacity,deformation ability,ductility and energy dissipation,strength degradation and stiffness degradation rules.The results showed that the I-type joints of had a mixed failure mode with a low-cycle fatigue damage in the heat-affected zone(HAZ)of the beam end weld and joint zone damage,and the failure mode of the IItype joints were local buckling and fracture in bottom flange and web of beam end.And the joints had favorable seismic performance with high strength,stiffness,deformation,energy dissipation capacity and ductility.The two kinds of ABAQUS finite element joint models of the CFST columnconcrete-filled U-shaped steel beamjoints were established.The simulated peak load was good agreement with the experimental value,and the stress concentration regions were matched with the experimental failure mode,which proved the validity of the models.Moreover,the influence of axial compression ratio,concrete strength,the channel thickness in the joint zone,reinforcement ratio of slab and the welding of the channel in the joint zone on the load capacity and failure modes were analyzed for the I-type joints.And the effect of the welding positions of steel beam,the channel thickness in the joint zone and straight beam on the load capacity and failure modes were analyzed for the IItype joints.Based on the results of experimental research and finite element analysis,some design and details suggestions for improving the CFST column-concrete-filled U-shaped steel beam joints in this study were proposed.