Behavior and model evaluation of large-rupture-strain (LRS) FRP-confined concrete-encased high-strength steel columns under axial compression

Fiber reinforced polymers (FRP)-confined concrete-encased steel columns (FCSCs) have become increasingly popular. However, few studies have been conducted on the FCSCs with a large-rupture-strain (LRS) FRP tube. To this end, the axial compressive behavior of FCSCs with a polyethylene terephthalate (PET) FRP tube (PFCSCs) is investigated in this study. A total of eighteen circular stub columns (i.e., two unconfined specimens, four PET FRP-confined concrete columns (PFCCs), and twelve PFCSCs) were tested under axial compression, in which the PET FRP tube thickness, the shape and nominal yield strength of the encased steel sections were the focal points. The results indicate that the steel strength can be fully utilized because local instability of the encased steel sections can be well suppressed by the surrounding concrete. The specimens with a circular steel tube had better performance than those with a cruciform steel due to the additional confinement provided by the circular steel tube. Moreover, a model assessment suggested that the models of Lin et al. and Zeng et al. could provide relatively satisfactory predictions for the ultimate stress and strain of confined concrete in PFCSCs. •The strain distribution of encased high strength steel tube is more uniform than that of cruciform steel column in PFCSCs.•In FCSCs, the encased steel sections not only confine the confined concrete, but also affect its integrity.•The confinement of encased cruciform steel section on the confined concrete in PFCSCs can be ignored.•The PFCSCs with an encased steel tube have a better composite action than those with an encased cruciform steel section.