Experimental Study On Seismic Behavior Of Bolted-welded Hybrid Connection Joints Of Square Steel Tube Filled Concret Column-Steel Beam With Outer End Plate Reinforcement

Concrete filled steel tube(CFST)joints are widely used in high-rise buildings,long-span buildings and bridges because of their high bearing capacity and good seismic performance.The state has also promulgated some relevant codes and regulations for concrete filled steel tubes,but there are still problems of fewer types of joints covered in the codes and regulations.In this paper,on the basis of steel beam to concrete filled steel tubular column bolted end-plate connections,the bolt-welded hybrid connection joint form of concrete filled square steel tubular column-steel beam with outer end plate reinforcement is proposed.In order to study the seismic performance of this kind of joint,three specimens of the bolt-welded hybrid connection joint of concrete filled square steel tubular column-steel beam with outer end plate reinforcement and one steel beam to concrete filled steel tubular column bolted end-plate connections joint are made.The quasi-static loading tests show that the failure characteristics,seismic performance index,bearing capacity and strain distribution of the specimens are obtained.The hysteretic curves,skeleton curves,ductility and energy dissipation capacity,strength and stiffness degradation of exterior end-plate reinforced bolted-welded joint and common through-bolted joint were compared and analyzed.The effects of end-plate thickness and stiffness ratio of beam to column on exterior end-plate reinforced concrete filled square steel tubular column-steel beam bolted-welded joint were studied.The test results show that the exterior plate reinforced concrete filled square steel tubular column-steel beam bolted-welded joint has higher bearing capacity and better energy dissipation capacity than the common piercing bolted joint specimens;reducing the thickness of the end plate will increase the ductility and energy dissipation capacity of the joint,but has little effect on the change of ultimate bearing capacity of the specimens;increasing the stiffness ratio of beam to column may change the joint.The failure mode makes the joint transit from beam end failure to column end failure;setting stiffeners and axillary plates in the joint area can effectively avoid the stress concentration phenomenon at the weld of steel beam and end plate,and make the plastic hinge move out,but the weld end is prone to weld defects,which is disadvantageous to the seismic resistance of the joint.In view of the lack of design methods for such joints in domestic codes,this paper summarizes the relevant codes(codes)for the design of concrete filled square steel tubular(CFST)and steel structure,expounds the design ideas of bolted-welded joint of CFST column-steel beam with external end plate reinforcement,simplifies the stress model of the joint,clarifies the mode of force transmission in the core area of the joint,and further derives the design ideas.According to the formula,the theoretical values of shear bearing capacity of the joint core area are calculated and compared with the experimental values.The results show that the shear values of the joint core area under yielding load and ultimate load are less than the theoretical values,indicating that the specimens have a certain shear reserve.For the joint specimens with column end failure,the theoretical value of shear bearing capacity calculated by the formula is smaller than that of the core area under the actual ultimate bearing capacity of the joint,which shows that the shear bearing capacity calculation formula proposed in this paper is safe and can be used in engineering.