Study On Seismic Behavior Of Special-shaped Column Composed Of Concrete-filled Square Steel Tubes

As a new type of column, special-shaped column composed of concrete-filled squaresteel tubes (SCFT column) was first introduced from the point of improving theconstruction house land utilization rate and increasing the house indoor area. In thispaper, SCFT column with no openings on the connection plates was presented.Thestructural mechanism is analyzed by presenting finite element model (FEM) of SCFTcolumn’s connection plates with/without openings. The two different types of modelsare then used for non-linear analysis of axial compression behavior and hystereticbehavior. The result shows that SCFT column without openings has higher ultimateaxial load bearing capacity. However, different types of connection plates did notshow evident difference in stiffness and yielding displacement. Under low cyclicloadings, column without openings shows lower ductility but higher ultimate loadbearing capacity and energy depleting capacity. Taking structural behavior andconstruction feasibility together into consideration, SCFT column without openingshas a more advanced overall structural performance.With parameters include concrete and steel strength, axial compression ratio andwidth-thickness ratio of the connection plate, FEM was created and analyzed underlow cyclic loading process. Increasing steel strength will enhance load bearingcapacity by the same time lower the ductility significantly; no evident signs imply theconcrete strength is related obviously to the load bearing capacity and ductility; thehigher axial compression ratio is the lower ductility column has and load bearingcapacity; with smaller width-thickness ratio of the connection plates the columnshows better ductility and smoother, complete stiffness degradation, it gains theoptimized energy dissipation when width-thickness ratio equals19. In general, it isconcluded that for the SCFT column with mono column sized100mm by4mm,width-thickness ratio ranged19to38, the coordination between mono columns andconnection plates is comparatively good and the column is structurally economicaland has the optimal earthquake resistance.The seismic performance was studied of the SCFT column-H-section steel beamframe,the frame has a good energy dissipation capacity and ductility. The higher axialcompression ratio and span of beam is, The failure mechanism of frame transitionsfrom the beam hinge failure mode to the column hinge failure mode. The increase of axial compression ratio has a adverse effects on the capacity, ductility and strengthdegradation of the frame. Filled wall in frame can effectively share the horizontal loadat the earlier stage, compared to the SCFT column frame without wall,the ultimatebearing capacity and elastic stiffness increased, but the energy dissipation capacitydecreased significantly, flexible connections or preinstalled extension joint issuggested regarding construction practice.The seismic performance of SCFT columns structure was studied by pushoveranalysis method. The12storey frame-brace model was established: firstly, thestructure sideway under frequent earthquake and rare earthquake separately meet thelimit requirements; secondly, the lateral resistant performance of the SCFT model isbetter than the CFST model with the same steel quantity; thirdly, the SCFT frame-brace system yield mechanism is: brace-beam-SCFT column, which can meet the "nodamage under frequent earthquake, no fall under rare earthquake " design goals;finally, to peasant demonstration project in Baodi district of Tianjin as the background,the analysis of mechanical properties of structural system was done.