Static Behavior Of Square Concrete-filled Double-skin Steel Tube T-joints

Concrete-filled double-skin steel tube(CFDST)is a new type of composite member developed from traditional concrete-filled steel tube(CFST).The bearing capacity of CFDST under rational design is not lower than that of CFST with the same dimensions and material properties of outer steel tube,and CFDST also inherits the advantages of CFST,including good plasticity and toughness,good fire resistance ability,ease of construction,etc.Moreover,CFDST has a lighter weight,a larger cross-section and bending stiffness and a better seismic performance compared with the CFST.Thus,CFDST has the potential to be used as bridge piers,legs of buildings and main pillars of truss and lattice structure.Joints are the key components of truss and lattice structure with CFDST chords.The safety of joints has a great influence on the reliability of the structure.However,the configuration and loading condition of CFDST joints are very complex with the interaction between inner and outer steel tube and the sandwiched concrete,and the failure modes and mechanism of CFDST joints are different from those of the hollow steel tubular truss joints.Therefore,it is very important to study the behavior of CFDST T-joints in the truss structure with CFDST chords.In this paper,the static behavior of CFDST T-joints is experimentally and theoretically investigated,and the main works are summarized as follows:(1)The study progress in the behavior of CFDST members,the performance of CFST under local compression and the static and fatigue performance of joints with CFST chord were reviewed.(2)Tests of 12 T-joints with CFDST chord and square hollow section(SHS)brace were carried out.The specimens were tested under lateral forces on SHS brace while a constant compressive load on CFDST chord.The influence of axial compression ratio of CFDST chord,diameter ratio between brace and chord and hollow ratio of CFDST chord on the performance of the specimens was investigated.(3)Based on the selection of the rational constitutive model of steel tubes and the sandwiched concrete,the behavior of CFDST T-joints was simulated by a finite element analysis model,and the predicted results generally agree well with the measured ones.