Various　accidental　loads　may　cause　local　damage　to　the　structure　and　even　lead　to　progressive　collapse.　Using　the　concept　of　secondary　defense　to　improve　the　progressive　collapse　resistance　of　steel　frame　structure‚　a　novel　principle　was　proposed.　The　new　concept　involves　installation　of　kinked　reinforced　bars　in　the　beam-column　joint　area　to　realize　alternative　path.　Pushdown　loading　test　and　numerical　simulation　were　carried　out　on　beam-column　frame　substructure　with　the　kinked　reinforced　bars‚　taking　into　account　the　diameter‚　kinked　height　and　length　of　the　reinforced　bars.　The　load-displacement　curve‚　failure　mode‚　deformation　capacity　and　catenary　development　of　the　specimens　were　compared.　The　results　show　that　the　reinforced　bars　result　in　even　deformation　of　the　substructure‚　and　encourage　symmetrical　deformation　of　the　left　and　right　beams　to　facilitate　two-force　tie　rods‚　a　case　which　improve　the　bearing　capacity　and　ductility　without　changing　the　plastic　hinge　movement　and　other　structural　characteristics.　The　reinforced　bars　participate　little　in　the　bending　action　of　the　steel　beam　in　the　elastic　state.　With　the　increase　of　displacement‚　the　reinforced　bars　gradually　change　from　the　bending　state　to　the　straightening　state　and　participate　in　the　stress　and　deformation　of　the　specimen‚　which　greatly　improves　the　internal　energy　provided　by　the　catenery　resistance　and　increases　the　catenary　contribution　coefficient　by　about　20%　.　It　is　also　found　that　the　ultimate　bearing　capacity　of　the　specimen　increases　and　then　decreases　with　the　increase　of　kinked　height　and　length　of　the　reinforced　bars‚and　the　failure　mode　also　changes　accordingly.　According　to　the　sequence　of　reinforced　bar　fracture　and　steel　beam　cracking‚　the　substructure　is　divided　into　two　failure　modes:　steel　bars　first　fracture‚　followed　by　steel　beam　cracking‚　and　steel　beam　first　cracking‚　followed　by　steel　bars　fracture.　When　the　kinked　height　is　close　to　30　mm‚　the　reinforced　bars　can　play　a　better　role　in　its　tensile　function　and　the　diameter　d　=　12　mm　can　better　match　the　commonly　used　kinked　height‚　and　avoid　reduction　in　the　bearing　capacity　of　the　specimens　caused　by　damage.　©　2023　Science　Press.　All　rights　reserved.