Behaviour of concrete-filled double skin rectangular steel tubular beam–columns

Double skin composite columns are formed from two steel skins filled with concrete in between. This new form of hybrid column has the potential to be used in many domains such as high-rise bridge piers and large diameter columns in high-rise buildings, etc. This paper describes a series of tests carried out on concrete-filled double skin steel tubular (CFDST) stub columns, beams and beam–columns. Both outer and inner tubes are cold-formed rectangular hollow sections (RHS). The failure modes, and load–deformation behaviour of CFDST specimens are compared with those of conventional concrete-filled steel tubular members and empty double skin tubular members. A theoretical model is developed in this paper for the CFDST stub columns, beams and beam–columns. Reasonably good agreement is observed between the predicted and tested curves. Simplified models are derived to predict the load-carrying capacities of the composite members.