Study On The Seismic Behavior Of Bolt-weld Joints Reinforced By Arc End-plates Connecting Circular Concrete-filled Steel Tube Columns To Steel Beams

Concrete filled steel tubular structure is widely used in high-rise,super-high-riseand long-span bridges because of their high bearing capacity and convenient construction.However,the research of beam-column joints is lagging behind the that of concrete-filled steel tubular structures.There are some problems in the joint of steel beam and concrete filled steel tubular column,such as the complex structure of the joint,the difficulty of construction and the redundant shape of the joint.Based on these problems,this paper presents a new type of bolted-welded joint reinforced by arc end-plates connecting circular concrete-filled steel tube column to steel beam.One ordinary full-bolted joint specimen and two joint specimens with external arc plate reinforced composite bolted-welded joints were designed in the scale of 1:2 and were tested under the later cyclic loads.The failure modes,hysteretic curves,skeleton curves,distribution of strain and displacement of the joint specimens are obtained.The ductility and energy dissipation capacity as well as the degradation of strength and stiffness of joint specimens were compared and analyzed.The influence of the change of beam-column linear stiffness ratio on the mechanical behavior of the new joint is studied.The new joints studied in this paper have two failure modes,one is the plastic hinge failure at the beam end and the other is the partial buckling failure at the column end.The core of the new type of joint is basically intact,which meets the design requirements of "strong joint,weak component".Compared with the normal bolted joint,bearing and energy dissipation capacity of the new type of joint is higher.With the increase of the linear stiffness ratio of beam to column,the bearing capacity of the new joint is greatly improved,but the failure mode of the joint may be changed.In the joint design,the ratio of Beam to column stiffness should be reasonably controlled.The vertical stiffener and the horizontal haunch plate should be set at the joint to make the plastic hinge of the steel beam move outwards,so as to avoid the stress concentration at the joint.The finite element model of the new joint is built by ABAQUS software.Comparison of results between the simulation and the test has shown good agreement.A series of parametric analysis have been carried out for the specimen J-3 based on the verified finite element model.The results show that except the axial compression ratio n=0.5,the area of the hysteretic loop is small and the hysteretic curves of other joint specimens are full.The joint specimens have good energy dissipation ability.With the increase of axial compression ratio,the ultimate bearing capacity of the joint decreases.When the axial compression ratio is greater than 0.5,the failure mode of the joint changes from plastic hinge failure of the steel beam to local buckling failure of the column.When the strength of the steel beam and beam-column linear stiffness ratio increases,the ultimate bearing capacity of the joint increases.The change of concrete strength has little effect on seismic behavior of the joint.