Mechanical Performance of Stiffened Concrete Filled Double Skin Steel Tubular Stub Columns under Axial Compression

This paper presents the mechanical performance of Concrete Filled Double Skin Steel Tube (CFDST) columns stiffened by Welded Reinforcing Bars (WRBs) under axial compression. A series of experiments were carried out on sixteen CFDST columns using two different D/t ratios and different patterns of WRBs as parameters. The steel reinforcing bars were welded either on the external surface of the inner tubes or on the internal surface of the outer tubes. Various patterns were used to enable a better understanding of the stiffened CFDST columns performance. Moreover, the compressive loading vs. end shortening curves, failure modes, strength index and concrete-steel contribution ratio were analysed. The results showed that a certain pattern of the WRBs affords additional ductility and strength capacity of the stiffened CFDST columns. Furthermore, WRBs play an important role in the mitigating failure modes and work consistently with the shell concrete of these columns. Design methods were developed for the calculation of the strength capacity of stiffened CFDST columns and assessed against the experimental results to trace the suitable formulation for design purposes. The outcomes of modified analytical procedures mostly match well with the experimental results of the stiffened CFDST columns.