Experimental Study On Seismic Behavior Of Space Joints Of Concrete-filled Steel Tubular Concrete Cross-pivot Columns And Steel Reinforced Concrete Beams

The handling of complex node connections in super high-rise structures generally plays a decisive role in securing the overall seismic performance of the structure.At present,a large number of experimental researchs on seismic performance of joints have been carried out at home and abroad,but mostly based on plane and static tests and with different specific projects,the conclusion is very universal.Therefore,This paper targets on complex space joints which formed by concrete-filled steel tubular columns and steel reinforced concrete beams used in a practical project,research on it's seismic performance and the low-cycle alternating test method,the topic has important engineering application value.This paper mainly carried out the following research works:(1)The current research status of steel tube concrete structure and steel reinforced concrete structure is expounded,and the existing problems are pointed out.(2)Take three key transition joints in an actual project as the research objects,they are subjected to a low-cycle repeated loading test by using a modified test loading scheme.Failure mechanism,crack development,load-displacement hysteresis curve,skeleton curve,strength and stiffness degradation characteristics,ductility and energy dissipation capacity are investigated.(3)Finite element analysis is performed on one of the nodes and compared with the test results.The damage conditions of concrete,stress of rebar and steel,and load-displacement skeleton curves are investigated.Through experimental research and simulation analysis,the main conclusions are as follows:1)Seismic performance and seismic construction measures of the joint meet the requirements,steel web should be set stiffeners or thickened.Destruction of the three specimens is similar,all three specimens experienced three same stages of flexible working,crack working and failure,concrete damage in hinge area is more serious than the ring beam,presents a typical "beam hinge" failure mode,most of the longitudinal beam rebars buckling fracture and individual beam steel web cracking.With the increase of cyclic loading displacement,the hysteresis loop becomes fuller,the enveloping area increases,and more energy is absorbed,The six hysteresis curves of three specimens show no obvious pinching phenomenon.With the increase of cyclic loading displacement,the loading stiffness of the specimen gradually declines,and the unloading stiffness changes little,at the end of the test,due to the plastic deformation of yield rebar and steel,there is a large residual displacement at the beam end.With the increase of cyclic loading displacement,bearing capacity gradually increases,bearing capacity decreases slowly after the peak,and bearing capacity is still high until the damage.The displacement ductility coefficient is greater than 2,specimens have large deformation capability and good ductility.Equivalent viscous damping ratio increases steadily with the number of cycles,explain that the speciments play a good role in energy consumption and the energy consumption performance is stable.2)Low-cycle alternating test scheme for complex joints is feasible,The method and results of the paper can provide reference for similar complex joints.