| Complex joints have been used more and more in super high-rise structures,but the current domestic and foreign research on key complex joints in super high-rise structures is not thorough enough.Nowadays,there are various types of joints in practical engineering.When designing these joints,the available information is extremely limited.The main reason is that the universality of the research object and conclusion of the past engineering joint test is not high,and the low cycle alternating test of the engineering complex joints is less,and the bearing capacity test is mainly used,which is difficult to meet the requirements of engineering design.This paper selects three complex joints of concrete-filled steel tube columns(composite columns)in actual engineering projects as the research object,simplified the joint model,and scaled it down to 1:6,and carried out low-cycle repeated load tests on them.The seismic performance of this type of joint is studied to test whether the design of the joint in the actual project has sufficient performance,and suggestions for the design and application of this type of joint in engineering are provided,which has important practical engineering guiding significance.The study in this paper mainly includes: seismic performance test,observing the distribution of concrete cracks at the beam end,column end and joint core area,steel plate yield and the final failure mode during the test.Analyze the seismic performance indicators such as hysteresis curve,skeleton curve,strength degradation,stiffness degradation,ductility and energy consumption.On the basis of the experiment,three finite element models JD1,JD2 and JD3 corresponding to the experiment were established using ABAQUS finite element software.The numerical simulation results were compared with the experimental results to verify the reliability of the experimental results.Then set up 9 finite element models with JD1 and JD2 as prototypes,and compare and analyze the influence of the symmetry of the beams on both sides of the joint on the mechanical properties of the joint;Four finite element models were established using JD3 as the prototype,and the influence of whether there is concrete in the Y-shaped steel tube joints on the seismic performance and bearing capacity of the joints was compared and analyzed.Through experimental research and finite element simulation analysis,the main conclusions are as follows:(1)The seismic performance and bearing capacity of the three joints are good,which meet the seismic design requirements of ’ strong joints and weak components ’.The failure mode of the specimen is mainly ’ beam hinge ’ failure in the joint area,which is flexural fracture at the plastic hinge of the steel beam(specimen JD1),tensile fracture of the steel bar at the plastic hinge of the reinforced concrete beam,and concrete crushing failure(specimen JD2 and specimen JD3).(2)For the asymmetrical beam joints on the left and right sides,the side with greater beam stiffness is more stressed and consumes more energy in the overall seismic performance,and the performance becomes more obvious in the later stage of loading.Compared with symmetric beam joints,asymmetric beam joints have poor ductility but smaller difference in bearing capacity.In actual engineering,when the loads on the beams on both sides of the joint are not equal and the seismic fortification requirements are not high,the asymmetric beam sections on both sides can be selected according to the load to obtain higher economic efficiency.(3)For Y-shaped steel pipe transition joints,pouring concrete in the steel pipe can effectively improve the bearing capacity and ductility of the joint.Extending to actual projects,pouring concrete in the bottom column steel pipe and the steel pipe in the core area of the joint to form a transition section for the joints with steel tube conversion is the most effective solution with good ductility,bearing capacity and engineering economy. |
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