Large scale fire tests and observations of actual building fires have shown that the fire performance of composite steel framed buildings is much better than is indicated by fire resistance tests on isolated elements. This contribution presents application of a simple design method, so-called FRACOF concept, for the analysis of non sway steel framed buildings with composite floors. Starting point were the outstanding results obtained in the BRE Cardington large scale building fire test programme carried out during 1995 and 1996. The method was further validated by large-scale standard furnace tests in 2008 and 2009, as well as with natural fire tests in 2010. A recent test has also shown the possibility of application of this concept to composite floors with castellated beams. The recommendations are in line with the reliability level imposed by current design rules and are limited to structures similar to that tested. The method permits designers to spare the fire protection for the framing elements for which it is not needed by keeping the same safety requirement than traditional codes.