This paper presents experimental information on the behaviour of sandwich box columns subjected to combined bending and axial loading. The sandwich box columns consisted of double thin-walled steel tubes with concrete between them. Owing to the interaction between steel and concrete, the composite members performed in a ductile manner during testing. Test results show that high strength/mass ratio characteristics were maintained, and the goal of obtaining significant member ductility was also achieved. The contribution of concrete to member performance was found to be more significant for members with higher steel width/thickness ratios. Copyright (C) 1999 John Wiley & Sons, Ltd.