This　paper　presents　the　experimental　and　numerical　investigation　on　resistance　of　two-storey　steel　sub-frames　subjected　to　a　middle　column　removal　scenario.　Two　different　types　of　1/2　scaled　steel　sub-frames　with　seismic　configuration　were　fabricated　and　tested,　they　are:　(1)　welded　connections　with　gross　beam　section　(GBS)　and　(2)　welded　connections　with　reduced　beam　section　(RBS,　typically　used　for　energy　dissipation　in　earthquake　design).　Based　on　the　test　results,　finite　element　models　using　explicit　software　LS-DYNA　which　can　accurately　replicate　the　response　of　the　frames　were　created　and　validated.　Using　the　validated　model,　the　parametric　studies　were　also　performed　to　investigate　the　effect　of　different　parameters　on　the　progressive　collapse　resistance　of　the　frame.　Base　on　the　experimental　and　numerical　studies,　the　failure　mechanism　and　collapse　resistance　capacities　of　these　two　types　of　frame　systems　are　first　time　investigated.　The　test　results　indicated　that　the　welded　connections　with　RBS　exhibits　better　performance　due　to　the　guaranteed　formation　of　plastic　hinges　at　the　location　of　reduced　section,　as　well　as　the　avoidance　of　welding　heat　effect　and　brittle　weld　fracture　at　beam　to　column　connections.　Thus,　RBS　exhibits　larger　deformation　capacity　which　is　favorable　in　mitigating　the　possible　progressive　collapse.　(C)　2020　Elsevier　Ltd.　All　rights　reserved.