Confinement-based direct design of circular concrete-filled double-skin normal and high strength steel short columns

By emphasising on the axial compressive resistance of circular concrete-filled double-skin carbon steel short (CFDST) columns, this paper proposes a direct design that takes into account the confinement effect of both outer and inner tubes. First, available test results of axially-loaded CFDST short columns were collected from the literature. Then, the results obtained from available resistance models, including design specifications, were compared with the test results. The comparisons revealed that most design models are conservative, some being too conservative, and all of them do not own the same accuracy along the entire slenderness range of the circular tubes, a fact attributed to the absence of confinement effect provided by the inner tube. Accordingly, the test resistances were used to obtain the lateral pressure (frp) due to the confinement effect provided not only by the outer tube (as in the previous studies) but rather by both outer and inner tubes of CFDST short columns with circular–circular and circular–square configurations. The calibrated formulae for frp were used to propose a design resistance formula for axially-loaded CFDST short columns. The results showed that these formulae provide much better resistances than the available predictors for any tube slenderness and for columns manufactured from different grades of steel and concrete materials.