ABSTRACT A test program on concrete‐filled double skin tubular (CFDST) beams with austenitic stainless steel outer tubes and high strength steel inner tubes is presented in this paper. A total of 22 four‐point bending tests was carried out to study the behaviour and strengths of CFDST beams. The stainless steel outer tubes were circular hollow sections (CHS) with average diameter‐to‐thickness ratios of 56.8 and 48.5, and the measured 0.2% proof strengths of 276 MPa and 300 MPa, respectively. The high strength steel inner tubes were also circular hollow sections (CHS) with diameter‐to‐thickness ratios ranging from 5.0 to 22.8, and corresponding measured 0.2% proof stress ranging from 433 to 1029 MPa. The annuli were filled with concrete with three different concrete cylinder strengths of 40, 80 and 120 MPa. The moment capacities, moment–curvature relationships and failure modes of the beams are reported in this paper. It should be noted that currently there are no design provisions for concrete‐filled stainless steel members. The test strengths were therefore compared with the moment capacity predictions in existing design codes (the European Code and American Specification) for concrete‐filled carbon steel tubes. The comparisons revealed that both design codes provide very conservative resistance predictions.
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