Compressive Behavior of Long Simple and Multi-Cell CFT Columns When Using Tie Bars Connector Elements

Concrete-filled steel tube (CFT) columns are increasingly used in high-rise structures due to their improved resilience to lateral loads. However, the behavior of multi-cell CFT columns, connected with different tie bar spacings, has been under-considered. This study aims to investigate the performance of simple and four-cell CFT columns with tie bars at different spacings. Seven columns with different tie bar spacings (100, 300, and 500 mm) were examined under axial compression. The load–displacement curve, failure pattern, and concrete core failure characteristics were described. A calculation model for the axial pressure field of simple and four-cell CFT columns with tie bars at varying spacings was constructed using a finite element analysis software. The results showed that the axial compression load capacity of confined CFT columns was significantly higher in four-cell composite specimens, where the capacity increased by 15.6% and 33% with tie bar spacings of 500 mm and 300 mm, respectively. Also, compared to simple CFT specimens, the capacity increased by 14.7%, 27.8%, and 42.6% with tie bar spacings of 100 mm, 300 mm, and 500 mm, respectively.