The　behaviour　of　hollow　structural　steel　(HSS)　stub　columns　and　beams　filled　with　normal　concrete　and　recycled　aggregate　concrete　(RAC)　under　instantaneous　loading　was　investigated　experimentally.　A　total　of　40　specimens,　including　30　stub　columns　and　10　beams,　were　tested.　The　main　parameters　varied　in　the　tests　were:　(1)　recycled　coarse　aggregate　(RCA)　replacement　ratio,　from　0　to　50%,　(2)　sectional　type,　circular　and　square.　The　main　objectives　of　these　tests　were　threefold:　first,　to　describe　a　series　of　tests　on　new　composite　columns;　second,　to　analyze　the　influence　of　RCA　replacement　ratio　on　the　compressive　and　flexural　behaviour　of　recycled　aggregate　concrete　filled　steel　tubes　(RACFST),　and　finally,　to　compare　the　accuracy　of　the　predicted　ultimate　strength,　bending　moment　capacity　and　flexural　stiffness　of　the　composite　specimens　by　using　the　recommendations　of　ACI318-99　(1999),　AIJ　(1997),　AISC-LRFD　(1999),　BS5400　(1979),　DBJ13-51-2003　(2003)　and　EC4　(1994).