Load introduction and transfer mechanism of K-type CFST circular section connections

This paper investigates the mechanism of load introduction and transfers for K-type concretefilled steel tubular (CFST) circular section connections experimentally and numerically. Six Ktype CFST connections were tested. Three-dimensional finite element (FE) models were then developed and validated against the test results, where the degradation and failure of the direct bond interaction were considered explicitly. The longitudinal strain distribution along the circumferential direction of chord-wall demonstrated that the non-uniform force transfer in the chord was caused by the one side load introduction through braces. The effects of the chord length, cross-sectional slenderness and interfacial interactions on the force transfer of tubeconcrete interface were evaluated: 1) the chord length above the connecting region has a positive influence on the force transfer; 2) for the K-type CFST connections in this study, the material strength of concrete in the chord with non-compact and slender sections could not be fully utilized due to the insufficient force transfer; 3) the direct shear interaction dominated the forcetransferring process from chord-wall to concrete for the compact section chord with reinforcing plates. Furthermore, the test and FE result confirmed that the load introduction length of the CFST chord with braces included the chord above the connecting region and the full connecting region. In addition, the equation of effective load introduction length for the CFST chord of the Ktype connections was proposed.