Influence Of External Stiffening Ring Splice Forms On Mechanical Properties Of Square Steel Tubular Column To H-shaped Beam Connections

In recent years, China’s steel output grows gradually, but our country steelstructure proportion is lower than that of developed countries. The steel structureindustry in our country still has a large development space.Steel structure building has superior construction convenience and good seismicperformance, in addition, it has characteristics of green environmental protection andenergy saving. The above advantages all conform to the construction concept ofresource-conserving society of China. Cold-formed square steel tube has reasonablemechanical properties, and then connection with stiffening ring and flange-plateconnection both have good seismic performance. Therefore, combined with theadvantages of the tube and two reinforced connections, a new connection type withstiffening ring is proposed, the beam of which is placed between upper and lower ringswhich welded on the tube. This method could avoid the local buckling of the ringscaused by lack of rings strength and stiffness. So it could well realize the seismicrequirement of shift-away of plastic hinge.Based on the new connection type, four kinds of splice forms of the rings aredesigned. And the mechanical properties of four connections are analyzed byexperiment and theoretical simulation. Specific as follows:Firstly, four connections are studied by experiment. The results show that the fourall realize the requirement of shift-away of plastic hinge. Failure process of thespecimens can be summarized as the following stages: plastic deformation of the beamflange, buckling deformation of the web, plastic hinge formation and failure of thespecimen. The connection JD-4whose rings were pieced together by X-shaped weldsdoes not finish loading because of the out-of-plane instability caused by manufactureerrors etc. Secondly, the plump load-displacement hysteresis curves of the specimensindicate that they all have good energy dissipation capacity. The connections havegood ductility performance and stable stiffness degradation. The plastic deformation ofthe beam is the main part of connection plastic deformation, in contrast, the sheardeformation of the panel zone makes less contribution to connection deformation.Beam plastic energy dissipation controls the specimen energy dissipation. Inconclusion, the performance of the connections is good.Thirdly, strain analysis results of the specimens show that the areas on the rings offour specimens between column angles and the fillet weld fields on the edges of thebeam flanges are the regions of stress concentration, thus the X-shaped welds whichlocate in the weak areas should be avoided. The parts of column which are welded onthe rings exist stress concentration. The strain of the certain flange area outside of theweld between the flange and ring is highest. In addition, this area is located at the placeof the plastic hinge approximately.Fourthly, the connection JD-2is simulation analyzed by finite element analysis(FEA) software ABAQUS, and the simulation results are in agreement with theexperimental results which prove the reliability and reference of FEA. The hysteresiscurves, deformation behaviors and the stiffness degradation trends of the simulationresults are consistent with that of experiment. The simulation results also prove that theareas on the rings between column angles and the fillet weld fields on the edges of thebeam flanges are the regions of stress concentration, so welds in these areas should beavoided in engineering practice.