Mechanical performances of stiffened and reinforced concrete-filled steel tubes under axial compression

Concrete-Filled Steel Tube (CFST) columns combine the benefits of high ductility and tensile strength of steel with high stiffness and compressive strength of concrete. It can be used in marine structures. This paper presents the mechanical performance of CFST columns strengthened by steel Reinforcing Bars (RBs) under axial compression. A series of experiments were carried out on 22 CFST columns using two different D/t ratios and different patterns of RBs as parameters. Furthermore, different diameters and numbers of RBs were utilized. The RBs were either welded on the internal surface of the steel tubes or embedded within concrete as a reinforced concrete. Various patterns were used to enable a better understanding of the strengthened CFST columns performance. Moreover, the compressive loading vs. end shortening curves, failure modes, strength index and RBs contribution ratio were analysed. The design methods of the ordinary CFST columns (EC4, AISC, Han, Yu, and Liang) were modified and assessed against the experimental results to trace the suitable formulation for design purposes. According to the theoretical results, the analytical formulations of certain methods are acceptable for the analysis of reinforced and stiffened CFST columns.