The　present　study　is　an　attempt　to　predict　the　time-dependent　behavior　of　concrete-filled　thin　walled　steel　RHS　(rectangular　hollow　section)　columns　by　means　of　a　model　that　is　proposed　by　the　ACI　Specifications　(ACI　Committee　209,1992)　[1].　A　theoretical　model　of　analysis　to　account　for　shrinkage　and　creep　effects　on　concrete-filled　steel　RHS　columns　under　sustained　loading　is　presented,　and　is　a　development　of　the　analysis　used　for　short-term　loading　(Han　et　al,　2001a)　[2].　A　comparison　of　results　calculated　using　this　model　shows　good　agreement　with　test　results.　The　main　objectives　of　this　paper　were　threefold:　firstly,　to　report　a　series　of　tests　on　the　behavior　of　concrete-filled　steel　RHS　columns　under　long-term　sustained　loading,　in　addition　to　providing　further　tests　on　the　static　ultimate　strength　of　the　composite　columns.　Secondly,　to　analyze　influence　of　several　parameters,　such　as　changing　steel　ratio,　long-term　sustained　load　level,　slenderness　ratio,　strength　of　the　materials　and　depth-to-width　ratio　on　the　capacities　of　the　concrete-filled　steel　RHS　columns.　And　finally,　to　develop　formulas　for　the　calculations　of　the　ultimate　strength　of　the　concrete-filled　steel　RHS　columns　with　long-term　sustained　loading　effects　are　considered,　such　formulas　should　be　suitable　for　incorporation　into　building　codes.　(C)　2003　Elsevier　Science　Ltd.　All　rights　reserved.