Performance of spirally reinforced high-strength circular CFST column under eccentric compression

CFST columns using high-strength concrete and high-strength steel are at risk of brittle failure after reaching peak load. The placement of internal spiral reinforcement is a promising technique to improve the strength and ductility of columns. This study devotes efforts to the eccentric performance of spirally reinforced high-strength circular concrete-filled steel tubular (CFST) columns. Experiments were conducted on spirally reinforced high-strength CFST columns and CFST counterparts. The strengths of concrete, steel tube, and spiral reinforcement were 108.5 MPa, 771.7 MPa, and 1597.6 MPa, respectively. Results demonstrated that the eccentric load-bearing capacity increased by up to 19.2% owing to the presence of spiral reinforcement, and the ductility was also enhanced. A finite element model was established for spirally reinforced CFST columns. Analysis verified that the increase in strength and ductility was attributed to higher material strength and larger high-stress region of concrete confined by spiral reinforcement. The load-bearing capacity of spirally reinforced CFST columns dropped slightly steeper than conventional CFST columns with the increase of the load eccentricity ratio. A design-oriented formula was proposed in this study, which provided conservative yet reasonably accurate strength predictions for spirally reinforced high-strength circular CFST columns.