Steel Buildings in Europe

Part 6: Fire Engineering 6 - 4 2.2.1 Structural fire engineering Structural fire engineering can be classed as a specific discipline within fire safety engineering, concerning the analysis of structural behaviour in fire conditions. The basis of fire design for building structures is set out in EN 1990, which states that fire design should be based on a consideration of fire development, thermal response and mechanical behaviour. The required performance of the structure can be determined by global analysis, analysis of sub-assemblies or member analysis, as well as the use of tabular data derived from analysis or testing and individual fire resistance test results. Considering the fire behaviour allows the designer to define the thermal actions to which the structural members will be exposed. In the prescriptive approach, the thermal action can be determined directly by use of a nominal time-temperature curve defined in EN 1991-1-2. For building structures, the standard time-temperature curve (the ISO curve) is normally used. Having determined the thermal actions, the thermal response of the structure should be considered using an appropriate method of heat transfer analysis to determine the temperature-time history of the structure. Finally, the mechanical behaviour of the member may be evaluated by analysis or testing to determine the resistance of the member given its temperature-time history. Depending on the intended function of a structural element, the acceptability of its mechanical behaviour may be assessed against one or more of the following criteria, evaluated either on the basis of analysis or fire resistance test.  Load bearing resistance ( R ) - the ability to resist specified actions without collapse during the required period of time in fire.  Insulation ( I ) - the ability to restrict the temperature rise on the unexposed surface below the defined limits of 140  C (average) and 180  C (maximum) to prevent the ignition of a fire within the adjacent spaces.  Integrity ( E ) - the ability to limit the development of significant sized holes through its thickness, to prevent the transfer of hot gas and spread of a fire into the adjacent spaces. The national regulations denote each of these three categories by using the above reference letter followed by the time requirement. For example a requirement of 60 minutes load bearing resistance for a given member would be expressed as R60. Note that load bearing resistance ( R ) is required for all load bearing structural elements. However, insulation ( I ) and integrity ( E ) are only required for separating elements, such as floor slabs and walls which form fire resisting compartment boundaries.