Mechanical Performance Research On Connection Of Concrete-Filled Double Steel Tubular Column To Steel Beam With RC Slab

Concrete-filled double steel tubular(CFDST)column was based on ordinary concrete-filled steel tubular(CFST)column,and the double steel tubes were provided to restraint the core concrete effectively.The bearing capacity,bending stiffness,ductility and energy dissipation capacity of CFDST column with the reduced section are improved,which exhibited good fire resistance,excellent seismic resistant and convenient construction condition.CFDST column can be widely used to high-rise buildings,bridge tunnels,underground space and other engineering structures due to these advantages.The joint of CFDST structure is the principle mechanical position for frame system.Existing researches have shown that the components of the composite joints connected CFDST column to steel beam work well together with the core region concrete.The typed composite joint has the high bending stiffness and bearing capacity,and the indexes of seismic resistant satisfying the requirements of specifications.However,the stress mechanical of the joint considering the composite effect of slab is uncertain,and further research is needed.The quasi-static experimental researches on the joint connected CFDST column to steel beam with RC slab were conducted in this paper.The stress mechanics of the composite joints were studied by the finite element analysis software.And the influences of parameters on the mechanical performance of the composite joints were also investigated.The main contents and conclusions are as follows:(1)Eight connections specimens of CFDST column to steel beam were designed and fabricated,considering the series of parameters,such as the composite effect of RC slab,the thickness of slab,anchorage web plate with ribs,infilled concrete in the circle steel tube,the type of joint and the axial load level.The tests of the composite joints were carried out under low-reversal horizontal loadings at the column end.The failure characteristic,hysteresis curves,skeleton curves,ductility,energy dissipation capacity,degeneration of bearing capacity and stiffness of the composite joints were analyzed in details.The restoring force model of loading-displacement for the composite joint was provided based on the experiments.The results showed that the main failure modes of the composite joint were fractures of the beam flanges and weld failures of the column wall.The bearing capacity and stiffness of the composite joint were improved by the anchorage web plate with ribs,infilled concrete in the circle steel tubes,and increased by the increasing of the slab thickness and axial load level.The energy dissipation capacity of the composite joints was better,and the ductility satisfying the requirements of the specifications.The hysteresis characteristic of the composite joints were obtained by the restoring force model proposed in this paper.(2)The finite element analysis(FEA)on the composite joint were conducted by the ABAQUS software.Well agreements were realized to verify the FEA models by comparing the hysteresis curves,skeleton curves,and failure modes between the simulation and the test.The force transferring mechanism of the composite joint and damage distribution of RC slabs were investigated based on the FEA models.And the results showed that the stress of the core area of the joint was concentrated on the variable cross-sections of steel beam flanges and anchorage web plates.The core conc ? rete filled in steel tubes was shown a diagonal-compression failure.Meanwhile,the RC slab near the column wall was damaged severely.The composite joint can transferred the load from the column to beam effectively,exhibiting favorable mechanical behavior.(3)The series of parameters analysis based on the benchmark specimen CBJ4 was conducted to study the influences on the moment-rotation of the composite joint of the RC slab thickness,axial compression ratio,compressive strength of core concrete,yield strength of steel tubes,bending capacity ratio of beam to column,steel ratio of the column section,etc.The formula of the initial stiffness of the composite joint was fitted according to the parameter analysis.Based on the three-parameter model,the M-? simplification equation of the composite joint was derived.The results of the theoretical formula were in good agreement with the numerical simulations.The initial stiffness formula and M-? relationship equation of the composite joint proposed in this paper can provide the theoretical foundation for the rigid judgment and the engineering designs in the future.