Behaviour of concrete-filled stainless steel tubular X-joints subjected to compression

Experimental investigation of concrete-filled stainless steel tubular X-joints fabricated from square hollow section (SHS) and rectangular hollow section (RHS) brace and chord members was conducted. High-strength stainless steel (duplex and high-strength austenitic) and normal-strength stainless steel (AISI 304) specimens filled with nominal concrete cylinder strength of 30 MPa were tested. The concrete was filled in the chord member of the test specimens along the full chord length. A total of 25 X-joint tests was performed that consists of 9 test specimens with brace members and 16 test specimens with steel bearing plates. The axial compression force was applied to the brace members, which were welded at right angles to the opposing sides of the continuous chord member. Local buckling failure of brace was the main failure mode observed during the tests. Therefore, steel bearing plates were used to simulate the brace members, which avoid failure of the brace members. These specimens were failed by chord face failure and chord side wall failure as well as crushing of concrete. The test results were compared with the design strengths calculated using the CIDECT design rules for concrete-filled carbon steel tubular structures. It is shown that the design strengths calculated using the existing design equations are quite conservative for the test specimens. It is recommended that the influence of stainless steel tubes on the bearing capacity of concrete-filled stainless steel tubular X-joints should be considered in the design rules.