Experiments on hybrid tubular K-joints with circular braces and square chord in stainless steel

An experimental investigation was conducted in this study on hybrid tubular K-joints with circular braces and square chord in stainless steel. A total of 14 hybrid tubular K-joints including 7 overlapped and 7 gapped K-joints were tested. All specimens were made of AISI 304 austenitic stainless steel. The failure modes, load-carrying capacities, and testing curves of axial load versus vertical displacement/chord deformation of all specimens were obtained. The influences of important geometric variations including brace diameter/chord width ratio (β), eccentricity (e), overlap ratio (O _v ) of overlapped tubular K-joints and gap distance (g) of gapped tubular K-joints were analyzed. It is shown that the load-carrying capacities of overlapped hybrid tubular K-joints are much greater than those of gapped hybrid tubular K-joints. It is also discovered that the load-carrying capacities increased with the increment of the β value, and increased with the decrement of the e value. Furthermore, the load-carrying capacities of overlapped hybrid tubular K-joints increased with the increment of the O _v value; however, the influence of the g value on the load-carrying capacities of gapped hybrid tubular K-joints is insignificant. It is demonstrated that the design formulae provided by CIDECT are generally unconservative; whereas the design formulae provided by EC3, AS/NZS and Chinese Code are all quite conservative for overlapped hybrid tubular K-joints. In addition, the design formulae provided by CIDECT and EC3 are generally conservative; however, the design formulae provided by Chinese Code are generally unconservative; and the design formulae provided by AS/NZS are generally appropriate for gapped hybrid tubular K-joints.