Tests of concrete-filled double skin (SHS outer and CHS inner) composite stub columns

Described are a series of compression tests carried out on concrete filled double skin tubes (CFDST) that consist of two concentric steel cylinders or boxes with the annulus between them filled with concrete. There are four possible combinations in constructing CFDST: 1) square hollow section (SHSS) as both outer and inner skins; 2) circular hollow section (CHS) as both inner and outer skins; 3) CHS as the outer skin and SHS as the inner skin; and 4) SHS as the outer skin and CHS as the inner skin. The strength, ductility and energy absorption of stub columns with the first three combinations were studied. This paper describes a series of tests on stub columns with SHS as the outer skin and CHS as the inner skin. Discussed are the conclusions and observations made based on the tests described in the paper.