Behavior Of Beam-Column Connections With Outer Tubular Joints In Steel Frames Under The Sudden Loss Of A Central Column

Throughout its life cycle,the building structure not only has to withstand common loads,but also may suffer from accidental loads such as explosions,earthquakes,and terrorist attacks,causing the progressive collapse of the building structure.In ordinary frame structure,the beam-column joint is the core part of its force transmission,which plays a vital role in resisting the progressive collapse of the building structure.The outer tubular joint is a new type of joint that can be applied to the fabricated steel structure.The outer tubular is welded to the cylindrical wall in the factory.The beam and column are connected by bolts on the site,and there is no inner diaphragm partition in the joint area.The whole joint is simple in structure and convenient in construction.However,this joint's performance under the condition of sudden failure of the column subjected to accidental load have not been researched.Therefore,this paper will study the performance of beam-column connections with outer tubular joints in steel frames under the failure of the central column.In this paper,a refined finite element model of all joints is established to study the mechanical behavior of the joints in steel frames under the sudden loss of a central column,and the validity of the model is verified by existing experimental phenomena and data.According to the different bolt diameters,the joints are divided into two groups.The common joints and outer-tubular joints with bolt diameter of 16 mm are compared.Study the deformation shape,failure mode and beam end rotation ability of the joint,and further reveal the stress process of the joint and the transformation process of the force mechanism.The variable parameter analysis of the outer tubular joint was carried out to study the thickness of the outer tubular,the thickness of the T-shaped web and the thickness of the T-shaped flange and the influence of the bolt diameter on the performance of the joint.The research shows that the plastic hinge position of the outer tubular joint is far away from the core area of the outer tubular joint,but after the cylindrical wall of the joint core area is increased,the joint stiffness increases,the deformability and the rotating ability of end of beam are weakened,which is not conducive to the development of the catenary mechanism resistance.The joint mainly relies on the vertical resistance provided by the bending mechanism to bear the upper load.The thickness of the outer tubular and the thickness of the flange of the T-shaped part have a great influence on the rotation ability and the degree of resistance development of the joint,while the thickness of the Tshaped web and the bolt diameter have less influence.Proposed more reasonable size parameters for the outer tubular joint.The results of the joint research can be used to simplify the evaluation of the resistance to progressive collapse of the frame structure.