Fiber-reinforced　polymer　(FRP)　confinement　has　been　demonstrated　to　be　efficient　in　enhancing　the　deformation　and　strength　capacities　of　concrete,　while　Polyethylene　terephthalate　(PET)　FRP-confined　concrete　easily　exhibits　a　strain-softening　stress-strain　behavior,　especially　for　PET　FRP-confined　concrete　in　square　columns.　In　this　study,　novel　PET　FRP-confined　FRP　spiral　reinforced　concrete　square　columns　(FCFRSCs)　are　proposed.　Capitalizing　the　benefits　of　internal　FRP　spiral　reinforcement,　the　strain-softening　behavior　of　PET　FRP-confined　concrete　is　expected　to　be　alleviated,　leading　to　excellent　mechanical　performance　of　the　proposed　square　columns.　The　axial　compressive　behavior　of　FCFRSCs,　as　well　as　square　concrete-filled　PET　FRP　tube　columns　(CFFTs)　and　FRP　reinforced　concrete　columns　(FRCs)　as　reference　columns,　were　investigated　via　experimentation.　The　experimental　results　show　that　the　strain　softening　behavior　of　confined　concrete　in　FCFRSCs　has　been　substantially　enhanced　with　the　internal　FRP　reinforcement,　confirming　the　viability　of　the　system.　The　strain　softening　behavior　of　FRP-confined　concrete　after　the　first　peak　is　prevented　and　a　hardening　behavior　is　achieved　for　concrete　in　FCFRSCs,　especially　when　the　GFRP　spiral　pitch　is　30　mm.