Externally　bonded　FRP　strips　can　effectively　improve　the　progressive　collapse-resisting　performance　of　existing　structures,　but　the　seismic　performance　of　structures　and　the　ease　of　construction　were　not　taken　into　consideration　in　existing　FRP　strengthening　schemes.　Numerical　simulation　was　performed　to　study　the　influences　of　strengthening　schemes　using　FRP　strips　on　the　seismic　and　progressive　collapse-resisting　behavior　of　cast-in-site　and　precast　concrete　frame　substructures,　by　which　the　strengthening　schemes　were　consequently　optimized.　The　detailed　numerical　models　of　concrete　frame　substructures　strengthened　with　FRP　strips　were　established　using　the　general　finite　element　(FE)　software　LS-DYNA,　in　which　the　concrete,　steel　reinforcement　and　FRP　strips　were　simulated　by　solid,　beam　and　shell　elements,　respectively.　The　bond-slip　of　steel　bars　and　FRP　strips,　the　bond　failure　between　precast　and　cast-in-site　concrete　and　the　loss　of　cross-sectional　areas　of　bars　at　the　mechanical　sleeves　were　considered　in　the　numerical　models.　The　numerical　models　were　validated　by　experimental　results,　which　showed　that　the　failure　modes　and　the　strengths　of　the　substructures　in　the　experiment　were　well　captured　by　the　numerical　models.　The　results　of　the　different　strengthening　schemes　suggested　that　the　bonding　of　the　longitudinal　FRP　strips　at　the　beam　bottoms　and　the　neutral　axes　of　beam　sides　and　U-shaped　transverse　FRP　strips　in　the　plastic　hinge　regions　of　the　beams　hardly　improved　the　structural　collapse　resistances　under　small　deformations　for　cast-in-site　concrete　substructures　(the　maximum　percentage　increase　was　only　2.6%).　Such　a　strengthening　scheme　had　almost　no　effect　on　the　seismic　performance　of　the　substructures,　while　the　progressive　collapse　resistance　under　large　deformations　was　increased　by　at　most　49.5%.　For　precast　concrete　substructures,　applying　longitudinal　FRP　strips　at　the　beam　tops,　beam　bottoms　and　bottoms　of　the　beam　sides　and　U-shaped　transverse　FRP　strips　in　the　plastic　hinge　regions　would　improve　their　maximum　resistance　under　small　and　large　deformations　by　at　most　24.2%　and　48.1%,　respectively.　Under　small　deformations,　their　collapse　resistance　was　increased　to　the　same　level　as　cast-in-place　ones,　which　was　advantageous　for　improving　the　seismic　performance　of　precast　concrete　substructures.　A　further　analysis　of　the　aforementioned　optimal　schemes　shows　that　keeping　the　amount　of　FRP　unchanged　and　at　the　same　time　increasing　the　covering　length　and　the　number　of　U-shaped　transverse　FRP　strips　applied　in　the　plastic　hinge　regions　of　the　beams　could　improve　the　structural　collapse　resistance　under　large　deformation,　while　the　effect　of　FRP　strengthening　on　the　collapse　resistances　under　small　deformation　remained　unchanged.　©　2022　Tsinghua　University.　All　rights　reserved.