This　paper　presents　both　the　experimental　and　numerical　studies　on　the　collapse　resistance　of　beam-column　substructures　with　all-welded　connections　under　a　middle-column　removal　scenario　induced　by　fire　scenarios.　Extensive　structural　responses　and　key　failure　phenomena　of　specimens　were　monitored　and　recorded　during　push-down　tests.　The　collapse　resistance　of　specimens　after　exposure　to　fire　deteriorated　by　comparison　with　those　without　fire　exposure.　In　general,　as　the　fire　temperatures　rose,　the　potentials　of　bending　mechanisms　against　the　progressive　collapse　were　gradually　degenerated,　and　the　corresponding　potentials　of　catenary　mechanisms　were　strengthened　instead.　Nevertheless,　the　effect　of　temperature　durations　on　the　development　history　of　resistance　mechanisms　was　almost　negligible.　Additionally,　an　abundance　of　elaborated　numerical　models　that　considers　the　damage　and　fracture　of　ductile　metals　was　developed　to　understand　the　structural　responses　of　post-fire　specimens.　The　simulated　results　showed　that　the　vertical　capacity　and　deformability　of　post-fire　specimens　were　greatly　enhanced　with　increasing　beam　heights.　The　span-to-depth　ratios　intrinsically　influenced　the　contribution　proportions　of　resistance　mechanisms　in　beam-column　substructures.　With　increased　span-to-depth　ratios,　the　vertical　capacity　provided　by　the　bending　mechanisms　decreased　obviously　and　deactivated　works　in　the　early　stage,　whereas　that　provided　by　the　catenary　mechanisms　entered　the　stages　of　rapid　development.　Furthermore,　two　typical　strengthening　solutions　after　the　fire　events　for　post-fire　sub-structures　were　comprehensively　compared　in　terms　of　the　structural　behaviors　against　progressive　collapse.　From　a　practical　viewpoint,　strengthening　with　welded　ribbed　plates　was　considered　a　superior　solution　for　the　post-fire　all-welded　connections.