This　article　describes　the　experimental　and　analytical　results　of　tests　on　two　medium-scale　steel　frames　to　investigate　the　collapse　behavior　of　a　heated　interior　column　in　steel-framed　structures　and　the　fire-induced　collapse　mechanism　of　the　structures.　Because　the　heated　column　in　the　structure　was　under　realistic　inelastic　end　constraints　(inelastic　effects　from　the　surrounding　cool　structures)　as　opposed　to　an　idealized　column　in　a　furnace,　the　tests　were　designed　to　investigate　the　effect　of　inelastic　end　constraints　and　different　load　ratios.　The　interior　column　subjected　to　fire　in　the　first　story　was　connected　with　a　force-measuring　bearing,　which　was　developed　to　measure　the　axial　force　in　the　heated　column.　This　article　presents　the　observations　and　analysis　results　of　structural　fire　behavior,　including　the　temperature　distribution　of　the　column,　the　development　of　deflection　and　axial　forces,　and　the　column　failure　modes.　The　results　show　that　the　effect　of　realistic　inelastic　end　constraint　is　not　significant　for　the　column　behavior　during　the　pre-buckling　stage,　compared　with　the　elastic　constraint,　but　it　is　significant　during　the　post-buckling　stage.　An　analytical　model　was　adopted　to　analyze　the　behavior　of　the　column　with　inelastic　end　constraint　under　fire.　Comparison　of　the　theoretical　and　experimental　results　shows　that　the　simplified　analytical　model　can　be　used　to　predict　the　collapse　behavior　of　the　interior　column　in　steel-framed　structures　under　fire.