Eccentric compression behavior of concrete-filled steel tube columns strengthened by CFRP/steel strip

Concrete-filled steel tube (CFST) column structures have been widely applied in structural engineering because of their superior bearing capacity and ductility. During the service lives of CFST columns, due to the change in the service function, the increase in the load, and the corrosion of the steel tubes, some existing CFST columns face the strengthening demand of increasing bearing capacity and durability. In this study, two efficient strengthening methods for CFST columns were proposed, namely, winding carbon fiber-reinforced polymer (CFRP) or welding steel strips around the columns. A total of 11 specimens were tested to investigate the behavior of the strengthened CFST columns under eccentric compression according to parameters such as the height-diameter ratio, fiber-reinforced polymer (FRP) layer, eccentric distance, and steel strip thickness. The results indicated that the ultimate strength and initial stiffness decreased with increasing eccentric distance. The arrangement of the FRP and steel strips effectively improved the eccentric carrying capacity and ductility. The improvement in the ultimate load due to FRP confinement exceeded 34.31%, and that due to the steel strips exceeded 13.47%. Finally, considering the effect of the eccentric distance and height-diameter ratio on the behavior of the structure under compression, a model for predicting the bearing capacity under eccentric load was proposed and verified by a database that included various design parameters.