The　spread　of　an　initial　local　failure　from　load-carrying　member　to　other　members　in　system　when　subjected　to　abnormal　load,　eventually　resulting　the　progressive　collapse　of　an　entire　structure.　This　paper　presents　an　experimental　and　parametric　study　on　the　anti-collapse　performance　of　moment　resisting　frames　(MRFs)　with　reduced-web-section　(RWS)　connections　under　critical　column　removal　scenario.　Factors　influencing　robustness　and　rotational　capacity　in　these　connections　under　Vierendeel　failure　are　analyzed.　A　total　of　14　laboratory　tests　on　steel　beam-column　connections　with　complete　joint　penetrations　are　presented;　one　test　was　conducted　with　solid　beam　connections,　while　the　others　were　designed　to　have　RWS　connections　with　different　circular　web　openings　geometric　parameters.　Comprehensive　finite　models　are　then　implemented　to　further　interpret　the　obtained　test　results.　The　test　results　demonstrated　that　vertical　resistance　against　the　applied　load　atop　the　failed　columns　was　totally　composed　of　flexural　action　(FA)　in　the　early　stages,　and　it　became　catenary　action　(CA)　as　the　vertical　displacement　of　the　failed　column　increased.　There　are　two　typical　failure　modes,　continuous　failure　in　the　beam-column　joint　region　generated　by　the　weld　line　fracture　and　interrupted　failure　in　RWS　connections　generated　by　the　fracturing　of　a　perforated　section,　and　the　different　failure　modes　determine　whether　the　system　can　develop　meaningful　catenary　action　when　the　initial　fracture　occurs.　Specimens　with　openings　exhibited　multiple　peak　loads　because　of　the　repeated　occurrence　of　local　damage　in　the　beam-column　connection.　RWS　connections　with　local　failure　near　the　openings　were　capable　of　developing　deformability　and　resistance　associated　with　CA　when　the　dimensions　and　location　parameters　of　the　opening　are　controlled　within　a　suitable　range,　and　the　rotational　capacities　of　these　connections　were　larger　than　the　connection　with　solid　beams.