Compressive strength and stiffness of concrete-filled double-tube columns

Concrete-filled double-tube (CFDT) columns have the potential to be widely used in high-rise buildings due to their very high load-carrying capacity, excellent ductility and good fire resistance. This new type of composite construction has attracted increasing research attention in the last decade, but there is a need to develop practical design recommendations for this construction. This paper aims to study the ultimate strength, the ultimate strain corresponding to the ultimate strength (ductility), and the stiffness of CFDT stub columns under axial compression. An existing finite element model is directly used to study square CFDT stub columns and this model is further modified to simulate circular CFDT stub columns under axial compression. Numerical data are generated to cover a wide range of parameters for CFDT stub columns. Through regression analysis, simple equations are proposed to calculate the ultimate strength, the compressive stiffness and the ultimate strain of CFDT stub columns. These equations can assist engineers to conduct structural analysis and design of CFDT columns.