Compression performance of concrete filled double skin steel tube columns

The inventive novelty of composite members is recognised as Concrete Filled Double Skin Steel Tube (CFDST) columns. CFDST comprises the concrete filled between the two-concentric steel tubes, where the inner tube is empty. The CFDST column could get equal or higher characteristics than the ordinary concrete-filled steel tube (CFST) columns, which the outer tube of CFDST performs as a concrete filled steel tube column, while the inner tube works as an unfilled tube. CFDST columns have been proven to have good characteristics in terms of the ductility, stiffness, strength and fire resistance. The main aim of this thesis is to experimentally explore the mechanical performances of CFDST columns by using the axial compression loads with different parameters. Several experimental procedures were carried out to understand the CFDST column performances. The proposed procedures discuss the topics of ductility, shortening, compression capacity, toughness, buckling, confinement effects, different performance indexes, bond strength, and failure modes. However, some specimens were tested to assess the impact of the parameters, which were used different type of concrete strength, dissimilar D/t ratios, dissimilar patterns of configurations and other variables as the main parameters in this thesis. Finally, methods which could predict the capacity of the CFDST columns were proposed and used versus experimental outcomes to specify appropriate formulation for design purposes.