CONTRIBUTION OF NON-STRUCTURAL CONCRETE WALLS TO THE FIRE RESISTANCE OF UNPROTECTED STEEL FRAMES

Abstract

In the scope of a new industrial building, an R60 fire resistance criterion was requested by the local fire brigade for the steel structure supporting non-structural EI60 concrete walls. On the basis of an investigation conducted after an actual fire in 2008, it was presumed possible to satisfy this R60 criterion using this type of unprotected steel frame. A 2D thermo-plastic model was set up, taking into account the thermal contribution of concrete walls, to limit excessive steel temperatures of the bearing elements. A void was considered between the concrete and the web of the middle columns to simulate real construction works as much as possible. The nominal ISO-834 fire was applied separately in each bay on the exposed parts of the elements. By using fixed column bases in case of fire, the structure can withstand up to 120 minutes of ISO fire i.e. far beyond the collapse of the primary structure subjected to fire. To avoid discussions about the local impact of a real fire, the investigation was extended to columns subjected to a local fire.