Behavior of Hollow and Concrete-Filled FRP-HSC and FRP-HSC-Steel Composite Columns Subjected to Concentric Compression

This paper presents an experimental study that was undertaken to investigate the effects of key parameters on the compressive behavior of fiber reinforced polymer (FRP)-concrete-steel composite columns that were manufactured with S-Glass FRP tubes. A total of 24 hollow and concrete-filled double-skin tubular columns (DSTCs), two concrete-filled FRP tubes (CFFTs), and six CFFTs with inner voids (H-CFFTs) were prepared and tested. The parameters examined included the inner steel tube diameter, influence of concrete-filling the inner steel tube, and the loading pattern. The results indicate that concrete-filling the inner steel tubes of DSTCs results in an increase in the compressive strength of confined concrete in DSTCs, compared to that of the companion specimens with hollow inner steel tubes. It was observed that cyclically loaded DSTCs exhibited slightly higher strength and strain enhancements compared to their monotonically loaded counterparts. The results also indicate that H-CFFTs perform significantly worse than DSTCs and CFFTs and their performance further degrades with an increase in the diameter of inner void. Comparison of the results from DSTCs and CFFTs indicate that both hollow and concrete-filled DSTCs exhibit improved compressive behavior compared to those of the companion CFFTs.