Steel Buildings in Europe

Part 6: Fire Engineering 6 - 42 6 USE OF NATURAL FIRE EXPOSURE AND ADVANCED STRUCTURAL MODELLING This Section introduces advanced calculation models that are used to demonstrate the actual behaviour of multi-storey buildings in fire and to explore more economic solutions for their fire design. 6.1 General To date, both the datasheet approach and the simple calculation models have been widely used in the fire design of multi-storey buildings. They have been shown to be adequate for the minimum life-safety requirements. However, they do not account for the features of a real fire and the interaction between structural members in a fire. In addition, increasing innovation in design, construction and usage of modern buildings have made it difficult in some situations to satisfy the legislative fire regulations economically using the simple calculation models. Therefore, advanced calculation models have been developed for fire design of multi-storey buildings. The advanced calculation models are based on the fundamental physical description of fire development, heat transfer and the structural response, which are simulated using numerical models. Therefore, they are able to give a more realistic and economic solution for the fire design of a structure. The advanced calculation models may be used to represent the behaviour of individual members, the whole structure or its sub-assemblies. They allow an appreciation of how buildings actually behave in a fire and give the option to design a more robust building. Performance-based design involves establishing performance criteria, defining fire actions, modelling heat transfer and simulating the structural response to the subsequently derived elevated temperatures, as briefly described below. 6.2 Modelling fire severity 6.2.1 Two-zone model Annex D of EN 1991-1-2 gives a two-zone model to determine the temperature caused by a localised fire. It assumes that combustion products within a compartment are accumulated in a layer beneath the ceiling. It divides the whole compartment with different fire conditions into a number of separated zones. Within each zone, the fire condition is assumed to be uniform, and the gas temperature is defined as a function of time by considering the conservation of mass and energy in the fire compartment. In each zone, the relevant differential equations are solved for the value of the temperature, using computer software. 6.2.2 Computational fluid dynamics (CFD) Annex D of EN 1991-1-2 proposes a computational fluid dynamic model (CFD) for a localised fire. CFD involves fluid flow, heat transfer and