Considering the effects of localised fires in the numerical analysis of a building structure

The methodologies that are used for analysing the fire behaviour of a structure that is subjected to a uniform thermal situation cannot be applied when the fire is localised. The concept of “zoning” can be applied: the structure is divided into several zones in which the situation is approximated as uniform. It is shown here that this division can lead to spurious forces in the structure. The structural code of the first author has been adapted in order to accommodate a continuous spatial variation of the fire environment. A series of uncoupled 2D thermal analyses is performed along the length of the beam finite elements and a series of 1D thermal analyses is performed across the thickness of the shell finite elements. After a discussion of the concept and the particularities dictated by the continuous thermal environment, the methodology utilised is explained and is shown in an example consisting of a composite steel concrete car park subjected to a localised fire of the type given in Eurocode 1.