| In the frame structure,the internal force transfer and distribution between the frame beam and column are carried out through the joint,joints can promote the cooperative work of the frame structure,but also can redistribute the internal force of the structure,and play a key role in maintaining the stability of the structure.There are many schemes for the connection between CFST column and steel beam in the existing standards in China,and then many scholars have created more types of beam-column joints on this basis,such as outer ring plate joints,inner partition joints,core joints,etc.In this paper,a new type of composite joint is designed according to the structural deficiencies of the existing joint and the failure characteristics of the beam-column joint in the earthquake disaster.The low cycle reciprocating load is applied to simulate the earthquake action,so as to reveal the stress mechanism of the new joint.At the same time,through theoretical derivation,numerical simulation and other ways to carry out in-depth research,the main contents and conclusions are as follows:The new composite joint is composed of compound concrete-filled steel tube column,steel beam,anchor web and upper and lower outer ring plate.By changing the number of bolts in the lower ring plate and the thickness of the outer ring plate,three new joints are designed and fabricated.The results show that the joints have good energy dissipation capacity and load bearing capacity,and the hysteresis curves are relatively full and close to"square".The skeleton curves are all standard "S" shape,which indicates that the joints have undergone elastic,molding development and failure stages completely.The failure form is the plastic hinge at the joint of the upper flange of the steel beam and the upper ring plate,which indicates that this type of j oint is conducive to exerting the late deformation ability of the joint and has a strong protection effect on the core area.The increase of the thickness of the outer ring plate can effectively transfer the load from the column end to the beam end,so that the plastic hinge is far away from the column wall when the composite joint is damaged,and the bearing capacity of the composite joint is obviously improved.With the increase of the number of bolts,the ultimate bearing capacity and energy dissipation capacity of joints increase,and the degradation rate of j oint stiffness decreases.The ABAQUS finite element model was established and verified based on the joint test results,and the force transfer mechanism of the joint was analyzed.The results show that the stress in the core area of the joint is more concentrated in the core area,the steel beam near the column wall side,and the welding position of the upper and lower ring plates.The upper and lower outer ring plate and the anchor web plate can transfer the load well,and the force transfer path between the composite members is clear.Based on the finite element model,TWBJ1 was used as the standard model to discuss the influence law of connection form,component parameters,load and other factors on the seismic performance of the joint.The practical calculation formula of bending moment-angle was obtained by fitting the three-parameter power model.The ratio between the results obtained by the practical calculation formula and the design value of the bending moment of the joint beam end ranged from 1.02 to 1.08.It shows that the practical calculation formula in this paper is of high precision and has certain reference significance. |
