08.29: Experimental investigation of concrete-filled double skin tubular stub columns with ferritic stainless steel outer tubes

ABSTRACT An experimental investigation of concrete‐filled double skin tubular (CFDST) stub columns with ferritic stainless steel outer tubes and carbon steel inner tubes is presented in this paper. A total of 14 tests was carried out to study the axial compressive behaviour and strengths of CFDST specimens. The outer tubes were cold‐formed from ferritic stainless steel material (grade 1.4003) into rectangular hollow sections (RHS) with depth‐to‐thickness ratios ranging from 26.1 to 42.1, while the inner tubes were cold‐formed from carbon steel (grade S235) into square hollow sections (SHS) with width‐to‐thickness ratios ranging from 7.5 to 13.5. The gaps between the outer and inner tubes were filled by concrete with three different nominal cylinder strengths of 40, 80 and 120 MPa. The columns had different lengths so that the length‐to‐depth ratio remained at a constant value of 2.5. The CFDST specimens were subjected to uniform axial compression. The column strengths, load‐axial strain relationships and failure modes were evaluated in this paper. The test strengths were then compared with the strengths calculated from the existing design codes, where the guidance given in European Code, Australian Standard and two American Specifications for concrete‐filled columns were used. It is shown that current design rules provide conservative predictions for the resistance of CFDST stub columns with ferritic stainless steel outer tubes.