In　a　reinforced　concrete　(RC)　flat　slab　structure,　the　external　columns　including　corner　and　edge　columns　on　the　building　perimeter　are　likely　to　be　more　susceptible　to　abnormal　and　accidental　loads　(such　as　vehicle　impact,　explosion,　fire,　etc.)　than　the　interior　ones,　causing　localised　damage　and　a　potential　progressive　collapse　of　the　overall　structure.　Current　research　has　mostly　focused　on　the　case　of　a　single　column　removal,　but　due　to　the　uncertainty　of　the　accidental　events,　the　likelihood　of　multiple　columns　being　simultaneously　destroyed　is　also　high.　This　study　will　develop　a　3D　high-fidelity　finite　element　model　using　the　LS-DYNA　program,　to　investigate　and　analyse　the　failure　behaviour　of　three　2 × 2　bay　RC　flat　plate　substructures　with　single,　two,　and　multiple　column　removals:　(i)　removal　of　a　corner　column　only　(Model　C),　the　accuracy　of　which　will　be　validated　with　our　previous　test　results,　(ii)　removal　of　a　corner　column　and　an　adjacent　edge　column　(Model　C_1e),　and　(iii)　removal　of　a　corner　column　and　two　adjacent　edge　columns　(Model　C_2e).　The　flexural　failure,　punching　shear　failure,　and　post-punching　mechanisms　of　the　models　will　be　discussed　based　on　their　crack　patterns,　deformed　shapes,　and　load-deflection　responses.　©　The　Author(s),　under　exclusive　license　to　Springer　Nature　Singapore　Pte　Ltd.　2024.