Research On Seismic And Bearing Performance Of New-type Joints Of Concrete-filled Square Steel Tube Columns And Steel Reinforced Concrete Beams

With the continuous development of China’s urbanization,the development of a new composite construction called concrete-filled steel tube,is popularized and applied wildly in engineering.To the composite construction of concrete-filled steel tube,the beam-column joint is the key position of its frame construction.Therefore,the joint research of concrete-filled steel tube column and beam,and its mechanical performance research,have great values of two sides,improvement of the beam-column joint design,and promotion of concrete-filled steel tube composite construction.In this paper,a new beam-column joint of concrete-filled rectangular steel tube column and shape-steel concrete beams has been put forward.Based on finite element model,the failure mode,load-bearing characteristics and seismic performances of the new joint have been researched.The main research contents and results are as follows.1.With the shape-steel concrete beam,The new joint of concrete-filled rectangular steel tube column and shape-steel concrete beams has been put forward.The whole shape-steel of main beam in joint area does not break off and passes through the joint area.Yet in secondary beam direction,the shape-steel breaks off in the joint area and passes through it,and the flange of the shape-steel is whittled.Meanwhile,outside the joint area,the shape-steel is spliced by cantilever shape-steel and middle one.The new joint not only is applied to joint with single beam but also works for joint with cross or T-shaped beam.2.Using the ANSYS software with powerful nonlinear function,the finite element model of the new joint has been established.In the modeling process,not only the non-linearity of material or geometry,but also the contact non-linearity between steel tube and core concrete are considered.With the models,the failure mode of new joint under low-cyclic repeated load has been studied.The finally failure mode is as follows.The whole concrete-filled steel tube column is in the elastic stage.However,the stresses of shape-steel,longitudinal steel,stiffening plate and concrete at root of beam have exceeded their yield strengths,which means large plastic deformation has been produced by the four parts.Therefore,when finally damaged,it is the large yield deformation(not shear deformation)at the root of beam that breaks solid elements of model at the same position and ends numerical analysis.The failure mode satisfies the design requirement of strong column and weak beam,as well as strong joint and weak component,which can overcome the deficiency of some joints in failure mode.3.The seismic performances of new joint under low-cyclic repeated load have been studied.Results are as follows.The energy dissipation ratios are between 0.67 and 0.73,which exceed the value of 0.5 and means the new joint owes good energy dissipation capacity.The displacement ductility coefficients are between 3.8 and 4.3,which exceed the value of 3 and means the new joint has good deformation ability.Stiffness degradation owns a similar normal distribution,and the degree of stiffness degradation gradually decreases with the increase of the displacement load of the beam end.Based on the energy dissipation capacity,deformation ability and stiffness degradation rule,it means the new joint has favorable seismic performances,which can overcome the deficiency of some joints in seismic performance.4.The bearing capacity of new joint under low-cyclic repeated load have been studied.Results are as follows.The maximum load of this single joint for office or commercial buildings is about 550KN and the one of this single joint for residential building is about 300KN.The results mean the new joint has favorable load-bearing characteristic,which can overcome the deficiency of some joints in load-bearing characteristic.5.To sum up,The failure mode is the form of strong column and weak beam,as well as strong joint and weak component,which can overcome the deficiency of some joints in failure mode.Based on the energy dissipation index,deformation index,stiffness degradation rule and the maximum load,it means the new joint has favorable seismic performances and load-bearing characteristic,which can overcome the deficiency of some joints in seismic performance or load-bearing characteristic.