Steel Buildings in Europe

Part 7: Fire Engineering 7 - 12 5 DIRECT USE OF SIMPLE ENGINEERING OPTIONS FOR USE BY NON SPECIALISTS This chapter gives an overview of current easy-to-use ‘simple’ calculation design rules, for assessing the fire resistance of steel and composite steel and concrete structural members. Specific simple design rules and design recommendations to satisfy specific safety requirements in terms of structural behaviour introduced recently in fire safety regulations of many European countries for single-storey storage and industrial buildings are given. It is noted that these methods are also applicable to other type of single-storey buildings. 5.1 Fire models 5.1.1 Nominal temperature-time curves EN 1991-1-2 [1] provides three standard fire curves, defining arbitrary hot gas temperature-time relationships in which no physical parameters of the fire load or fire compartment are taken into account. The most commonly used relationships in building design and in regulation prescriptions is the standard temperature-time curve (standard ISO fire) which represents a fully developed compartment fire. The second curve, the external fire curve, is intended for façade elements and the third curve is the hydrocarbon fire curve, representing a fire with hydrocarbon or liquid type fuel. The nominal temperature-time curves are defined as follows:  For standard temperature-time curve (standard ISO fire ) : (8 1) 20 345log 10    t g  (1)  For the external fire curve: ) 20 0,313 660 (1 0,687 3,8 0,32 g       t t e e  (2)  For the hydrocarbon fire curve: ) 20 0,675 1080 (1 0,325 2,5 0,167 g       t t e e  (3) where: θ g is the gas temperature in the fire compartment [°C] t is the time [min] It is important to note that the previous curves are reference curves. They do not represent the real thermal effect of a fire. The temperatures given by these curves always increase with time, without considering the limited fire load. The standard fire resistance rating required for structural members (expressed in terms of time) does not therefore indicate the actual time for which they will survive in a building fire.