Axial strength of concrete-filled double skin steel tubular (CFDST) columns with preload on steel tubes

Concrete filled double skin steel tubular (CFDST) columns have some advantages when compared to conventional concrete filled steel tubular (CFST) columns, such as lighter self-weight and better cyclic performance. CFDST columns have the potential to be used in structures such as bridges, high-rise buildings, viaducts and electricity transmission towers. The inner and outer steel tubes will be subjected to preloads from upper structures and wet filled concrete. The initial stresses and extra deformations on steel tubes caused by these preloads would affect the capacity of the CFDST members. This paper thus discusses the behaviour of axially loaded CFDST columns with preload either on the outer tube alone or on both tubes. A general purpose finite element analysis (FEA) model is developed to predict the behaviour of CFDST columns with the steel tubes subjected to preload. The FEA model is verified using test results of CFDST columns without preload and those of CFST columns with preload. The influences of preload ratio, slenderness ratio, hollow ratio and material strength on axial strength are discussed. Finally, formulas are proposed for calculating the ultimate strength of CFDST columns with preload on steel tubes.