This　paper　reported　a　series　of　hysteretic　torsion　experiment　to　investigate　the　torsional　behavior　of　rectangular　hollow　reinforced　concrete　(RHRC)　column　strengthened　by　fiber　reinforced　polymer　(FRP).　Six　RHRC　column　specimens　with　different　number　of　longitudinal　reinforcements,　spacing　of　stirrup　and　strengthening　method　using　FRP　were　designed.　One　was　not　strengthened,　four　were　strengthened　with　CFRP,　one　was　strengthened　with　CFRP　and　GFRP.　The　experimental　results　showed　that　the　primary　failure　modes　of　specimens　were　the　spalling　of　surface　concrete　with　the　detachment　of　FRP.　In　details,　under　the　hysteretic　torsional　load,　the　interaction　between　adhesive　and　concrete　caused　the　intersecting　diagonal　cracks　in　the　internal　concrete.　Compared　with　the　hysteretic　curve　of　specimen　without　FRP　strengthening,　FRP　strengthening　can　significantly　improve　the　initial　stiffness　by　50　%　and　peak　torsional　strength　by　70　%.　For　RHRC　column　without　strengthening,　the　fullness　was　poor　because　of　the　weak　torsional　energy　dissipation.　The　FRP　strengthening　can　also　enhance　the　torsional　energy　dissipation　and　seismic　behavior　of　RHRC　column.　To　predict　the　complex　torsional　behavior　of　RHRC　column　strengthened　by　FRP,　a　finite　element　(FE)　model　and　a　constitutive　model　were　developed.　The　FE　model　considered　potential　cracks　in　concrete　and　FRP–concrete　interface　based　on　the　application　of　the　cohesive　zone　model　(CZM),　whereas　the　constitutive　model　accounted　for　interface　damage　and　plasticity.　The　results　of　the　performed　simulations　indicated　that　the　proposed　model　can　effectively　represent　the　hysteretic　mechanical　behavior　of　columns　under　torsional　load,　which　cannot　be　achieved　using　conventional　FE　methods.　©　2024　Institution　of　Structural　Engineers