Seismic Performance And Theoretical Analysis Of Semi-rigid Composite Joints To Circular Concrete-filled Double Skin Steel Tubular Columns

The semi-rigid composite joints to concrete-filled double skin steel tubular（CFDST）columns are an important part of the composite structure.The beam-column joints of the frame have been treated into rigid or hinge connection in the traditional design and analysis.However,most of the connections,semi-rigid connections,are between rigid and hinge connection in the engineering practice.Presently,the tests and studies of the blind bolted composite joints to circular CFDST columns haven’t been reported.Due to the advantages of assembly construction,superior seismic performance and so on,the research possesses great significance.In this paper,the seismic performance and failure mechanism of semi-rigid composite joints to circular CFDST columns are studied by means of experimental verification and finite element（FE）analysis.The research work is as follows:（1）A test was carried out on four semi-rigid composite joints to circular CFDST columns under the low-cyclic loading.Loading on the column end was adopted,and the test parameters include column hollow ratio and end plate type.The detailed studies were conducted on the hysteresis and skeleton curves of relationship of loading（P）-displacement（△）and moment（M）-rotation（θ_r）,strength and stiffness degradation rules,ductility,energy dissipation,failure modes and the strain distribution rules of critical parts,etc..（2）FE analysis models of semi-rigid composite joints to circular CFDST columns were establish by using ABAQUS software,appropriate constitutive models of concrete and steel materials were employed,reasonable boundary conditions and loading methods were applied,and nonlinearity of geometry,materials and complex contact were considered.The nonlinear whole process was analyzed for the composite joints under low-cyclic loading.The FE analysis results were compared with the experimental results,and the correctness of the structural model was verified.（3）The influences of different materials,loads and geometric dimensions parameters such as the steel beam yield strength(f_y,b),the steel tube yield strength(f_y,c)and concrete strength(f_cu),axial compression ratio,blind bolt diameter and end plate thickness on bearing capacity and initial stiffness of the blind bolted composite joints to circular CFDST columns of were analyzed by using ABAQUS software.It provides guidance and reference for engineering application.（4）The effects of different construction measures on the semi-rigid composite joints to circular CFDST columns were discussed,such as welding plate within the column,welding steel tube outside the column,setting stiffener,beam flange with tapered haunch,weaking beam flange and prefabricated floor slab.The results provide references for practical engineering and prefabricated procedure of semi-rigid composite joints to CFDST columns.