Current　research　studies　on　progressive　collapse　of　reinforced　concrete　(RC)　moment　frames　mainly　focus　on　the　RC　frames　with　strong　horizontal　restraints　in　which　collapse　only　propagates　in　the　vertical　direction.　Notwithstanding,　progressive　collapse　may　propagate　in　the　horizontal　direction　due　to　insufficient　lateral　stiffness　and　bearing　capacity　of　the　real-world　structural　systems,　eventually　triggering　a　wider　range　of　damage　associated　with　a　disproportionate　collapse.　A　static　collapse　test　on　three　asymmetric　beam-column　substructure　specimens　with　flange　slabs　was　conducted　to　analyse　the　effects　of　different　lateral　restraints　on　the　progressive　collapse　behaviour　of　RC　beam-column　specimens.　The　three　specimens,　including　two　one-story　and　one　two-story　substructures,　are　designated　as　OP,　TP　and　OA,　in　which　OP　and　OA　represent　one-story　penultimate　and　antepenult　column　removal　scenarios,　respectively,　while　TP　represents　a　two-story　penultimate　column　removal　scenario.　Comparing　to　OP,　an　extra　bay　and　an　extra　floor　were　added　in　OA　and　TP,　respectively,　to　create　different　horizontal　restraint　scenarios.　Experimental　results　show　that　under　the　compressive　arch　action　(CAA),　the　contribution　of　the　CAA　within　the　beams　and　slabs　in　OP　and　TP　was　significantly　reduced　compared　to　that　in　OA.　Under　the　catenary　action　(CA),　the　collapse　resistance　of　OA　was　found　to　develop　rapidly　to　exceed　even　the　peak　resistance　of　CAA,　whereas　the　resistance　of　OP　and　TP　varied　marginally,　caused　by　the　continuously　released　axial　force　of　rebars　within　the　beams　and　flange　slabs.　Additionally,　the　final　failure　mode　of　all　three　specimens　demonstrated　a　compression-bending　failure　of　the　edge　and　penultimate　columns.　Subsequent　to　the　experiments,　a　fibre-beam-element-based　model　was　built　to　analyse　the　development　of　the　internal　forces　within　the　slab-flange　beams　and　columns.　In　the　numerical　analyses,　the　penultimate　column　in　OA　was　found　to　damage　prior　to　the　edge　column,　owing　to　its　larger　axial　force　generated　from　the　redistributed　force　and　the　additional　bending　moment.　While　in　TP,　the　so-called　Vierendeel　truss　action　led　to　an　uneven　internal　force　distribution　developed　within　the　two　floors,　causing　the　failure　to　propagate　from　the　lower　story　to　the　upper　story.　Finally,　design　recommendations　are　provided　based　on　the　results　obtained　from　the　experimental　test　and　numerical　simulation.