This　paper　presents　a　fibre-beam-element　based　model　to　capture　the　progressive　collapsemechanisms　of　reinforced　concrete　(RC)　frames.　The　model　is　comprised　of　rectangular　and　T-section　fibre-beam　elements.　A　stress-strain　relationship　for　the　steel　which　considers　the　embedment　of　the　reinforcing　bars　in　the　concrete,　the　effect　of　concrete　confinement　and　the　bond-slip　between　the　concrete　and　reinforcements　are　also　considered　in　the　model.　The　accuracy　of　the　model　is　verified　against　experimental　tests　performed　on　two　asymmetric　one-story　beam-column　specimens　with　flange　slabs　under　different　lateral　restraints.　The　first　specimen,　referred　to　as　＂OP＂,　was　a　two-bay　frame　subjected　to　a　penultimate　column　removal　scenario,　while　the　other　one,　referred　to　as　＂OA＂,　was　a　three-bay　frame　with　an　antepenult　removal　scenario.　The　simulation　results　agree　well　with　the　experimental　results　with　prediction　of　the　peak　capacity　being　within　10%.　The　model　is　then　used　to　gain　an　in-depth　understanding　of　the　failure　mechanisms　of　the　two　tested　specimens.　Numerical　results　reveal　that　the　progressive　collapse　resistance　of　the　RC　frames　is　primarily　determined　by　the　bending　stiffness　and　capacity　of　the　columns.　Compared　to　OP,　the　extra　bay　in　OA　provided　a　larger　horizontal　restraint　to　the　damaged　beam-flange　slab,　leading　to　115%　and　650%　larger　axial　forces　at　the　peak　resistances　under　the　stages　of　compressive　arch　action　(CAA)　and　catenary　action　(CA),　respectively.　Furthermore,　the　penultimate　column　in　OA　was　found　to　damage　prior　to　its　edge　column,　owing　to　its　close　proximity　to　the　missing　column　and　the　additional　bending　moment　MF　generated　by　the　redistributed　axial　forces　to　the　columns.