Finite Element Analysis Of The Mechanical Performance Of Steel Frames With "Upper Flange Welded-Lower Flange Bolted" Joints

In recent years,with the progress of modern industrial technology and the introduction of new construction industrialization policies,the assembled building has been vigorously promoted in China.Due to its advantages of high strength,lightweight,excellent ductility,short construction period and eco-friendly recyclability,steel structures have become the preferred choice for assembled buildings.Simultaneously,the study of beam-column joints in steel structures has become a key topic.As the research progresses,it is found that the spliced beam-column joints with cantilever beams have good energy dissipation capacity and ductility under earthquake action.The "upper flange welded-lower flange bolted" joint is a new type of spliced joint with a cantilever beam,where the upper flange of the joint is connected by butt welds and the lower flange is connected by spliced plates.This joint is easy to position in the construction,and the upper flange of the joint beam is flat to facilitate the laying of the floor slab.In order to study the overall mechanical performance of the "upper flange welded-lower flange bolted" in a steel frame,the joint was configured in a steel frame,and the mechanical performance of the steel frame under monotonic and low cyclic reciprocating loads is simulated and analyzed by ABAQUS software.In order to study the overall mechanical performance of the "upper flange weldedlower flange bolted" joint in steel frames,this paper commences with a comparative analysis of its mechanical performance against those of an ordinary joint steel frame.Secondly,by changing the width and thickness of the flange splice plate and the friction coefficient of the contact surface,three groups of 12 specimens were designed and finite element analysis was carried out to compare the seismic performance indexes such as hysteresis performance,bearing capacity and stiffness degradation,and energy dissipation capacity of the specimens with different joint splice parameters.Finally,the effects of axial compression ratio,slenderness ratio of column(floor height),and beamto-column linear stiffness ratio(beam span)on the force performance of steel frames with "upper flange welded-lower flange bolted" joints were considered,and three groups of 12 specimens were designed to compare and analyze the seismic performance indexes of the specimens with different parameters.The results show that:(1)Compared with the ordinary joint steel frame,the "upper flange welded-lower flange bolted" joint steel frame has stronger deformation and energy dissipation capacity,better ductility,slower degradation of bearing capacity and stiffness,and better seismic performance.(2)Under low cyclic reciprocating loading,the beam splice zone of the "upper flange welded-lower flange bolted" joint steel frame shows large plastic deformation,which eventually leads to damage to the steel frame.During the whole loading process,the steel frame dissipates energy through friction between the splice plate and the steel beam in the early stages,and in the later stages mainly through the deformation of the plate near the beam splice area.Steel frames exhibit good energy dissipation and ductility.(3)If the width and thickness of the flange splice plate are increased appropriately,the bearing capacity and energy dissipation capacity of the steel frame will be increased and the degradation of the bearing capacity and stiffness will be slowed down.It is recommended that the flange splice plate should be 20～40 mm wider than that of the lower flange of the beam,and the flange splice plate should be 2 mm thicker than that of the lower flange of the beam.Contact surface friction coefficient has a certain impact on the mechanical properties of the steel frame,the greater the friction coefficient,the better the seismic performance of the steel frame.It is recommended that the friction coefficient should be 0.4～0.5.(4)As the axial compression ratio increases,the bearing capacity,stiffness,energy dissipation capacity and ductility of the steel frame are significantly decreased,and the stiffness degrades more rapidly,which should be strictly limited in the design of steel frame structures.The increase of slenderness ratio of column will lead to the reduction of energy dissipation capacity and bearing capacity of steel frame,but the ductility of each steel frame is good.With the beam-column linear stiffness ratio decreasing,the bearing capacity,stiffness,and energy dissipation capacity of the steel frame are reduced,stiffness degrading more slowly,but its ductility is not significantly affected.