Static Behavior Of Concrete-Filled Double-Skin(CHS Inner And CHS Outer) Steel Tube T-Joints

Concrete-filled double-skin steel tube(CFDST)is a new kind of composite member,which not only inherits the excellent characteristics of concrete-filled steel tube(CFST),but also has the advantages of lighter weight and better bending resistance.CFDST has many different cross-section forms,e.g.circular hollow section(CHS)inner and CHS outer,square hollow section(SHS)outer and SHS inner,etc.The CFDST with CHS outer and CHS inner not only has better mechanical properties than that with SHS outer and SHS inner,but also has a more concise and beautiful appearance.Currently,CFDST with CHS outer and CHS inner has been used as bottom chord in the truss of some large transmission towers in China.The intersecting connections are commonly used in tubular trusses as the joints,and the performance of these joints directly affects the reliability of the truss structures.However,the research on the intersecting joints of CFDST with CHS outer and CHS inner is very rare.Therefore,the study on the static performance of the common T-shaped intersecting joints in the truss structures has an important engineering application value,and can make up for the deficiency of current theoretical research.This paper experimentally and theoretically investigates the behavior and mechanism of circular CFDST T-joints,and the main research works are summarized as follows:(1)Reviewing of the past researches related to this study,including the mechanical properties of circular CFDST members,the static and dynamic performance of CFST intersecting joints,was carried out.(2)Twelve T-joint specimens,including 2 specimens with CHS chord,2 specimens with circular CFST chord and 8 specimens with circular CFDST chord,were tested.The influence of outer diameter ratio between brace and chord,hollow ratio of chord and axial compression ratio of chord on the static behavior of the specimens was investigated.In the meantime,the performance comparison of T-joint specimens with CHS,circular CFST and circular CFDST chord was also carried out.(3)A finite element analysis(FEA)model for the static behavior of CHS brace to circular CFDST chord T-joints was built using the large general software ABAQUS.The predicted mechanical properties are generally in good agreement with the measured results.(4)Based on the validated FEA model,the effects of outer diameter ratio between brace and chord,nominal steel ratio of chord,hollow ratio of chord,slenderness ratio of chord,axialcompression ratio of chord,strength of the sandwiched concrete in the chord,width-to-thickness ratio of inner tube in the chord,diameter-to-thickness ratio of brace,length-to-diameter ratio of brace and yield strength of steel(inner and outer tube in the chord and brace tube)on the static behavior and mechanism of CHS brace to circular CFDST chord T-joints are systematically analyzed.