Steel Buildings in Europe

Part 7: Fire Engineering 7 - 55 (as purlins) as well as façades elements fixed on columns (concrete walls, sandwich panels, steel sheeting), so that out-of-plane collapse does not occur. In a 3D analysis, several parallel portal frames, the roof structure (purlins) and eventually bracing system are explicitly modelled (see Figure 6.5). The main difference in this 3D analysis is that the interaction effects between members will be directly dealt with; load redistribution from heated parts (weakened parts inside fire compartment) to cold parts (stronger parts outside fire compartment) can be taken into account in an accurate way and the global behaviour of structures will be analysed, providing a more realistic situation of mechanical response of structures in fire. Computation cost with a three- dimensional analysis is high because of significant number of elements used in the modelling. The choice between 2D and 3D analysis will depend on several parameters, such as the type of structure (steel or composite frame), the dimensions of the single-storey building, the fire scenario and objectives of structural fire design (to fulfil a prescriptive requirement, or to verify a failure mode). Fire wall Figure 6.5 Example of 3D mechanical modelling The basic finite element set-ups used to represent the structural members of frame are given below. Solid elements are omitted. as they are numerically too expensive.