Fibre Reinforced (FRP)-confined concrete-encased steel composite columns (FCSCs) are an emerging form of hybrid columns. The idea of a combined use of FRP-confined concrete and an encased steel section not only offers a durable and ductile structural form for new construction, but also can be practiced as an efficient method to retrofit/strengthen deteriorated steel columns. This paper presents a series of axial compression tests on concrete-encased steel columns confined with Large Rupture Strain (LRS) FRP composites, namely, Polyethylene Terephthalate (PET) FRP composites. A total of 12 circular specimans, including 6 FCSCs and 6 FRP-confined concrete circular columns (FCCCs) were tested, with the main test variables being the thickness of the FRP tube. The test results shoed that FCSCs with PET FRP possessed excellent performance in terms of both axial strength and ductility.