Preliminary investigation into behavior of beam-columns of concrete filled double skin rectangular hollow sections

Concrete filled double skin steel tubular (CFDSST) members can be recognized as a new kind of concrete filled steel tubular (CFST) construction. They consist of two concentric steel tubes with concrete sandwiched between them, the steel tubes can be circular hollow sections (CHS), square hollow sections (SHS) or rectangular hollow sections (RHS). The CFDSST columns have almost all the same advantages as traditional CFST members. Moreover, they have lighter weight, higher bending stiffness, and have better cyclic performance. It is also expected that CFDSST columns will have higher fire resistance capacities than their CFST counterparts, due to the inner tubes of the former being protected effectively by the sandwiched concrete under fire condition. In the past, many studies have been performed on CFDSST members with circular or square sections. However, no CFDSST member with rectangular section was investigated, which is more favorable to be used when it is subjected to large major-axis bending moment. This paper studies the behavior of CFDSST columns where both inner and outer tubes are RHS. Theoretical models are presented to predict the load-carrying capacities of the composite members.