Torero, JL 2014, 'Structural fire behaviour: a necessary component of structural optimization', in ST Smith (ed.), 23rd Australasian Conference on the Mechanics of Structures and Materials (ACMSM23), vol. I, Byron Bay, NSW, 9-12 December, Southern Cross University, Lismore, NSW, pp. 23-31. ISBN: 9780994152008.
Designers of structures, as any other designers, are under constant pressure to optimise structures. Complex methodologies have been developed to iterate structural designs until an optimized solution is obtained. The desired output being: maximization of strength while minimizing weight, cost and any other parameter that negatively affects the sustainability of the structure. Once this process is achieved, prescriptive fire resistance requirements are met by introducing homogeneous fire proofing through the entire structure as demanded by codes, independent of the function of any particular structural element. The procedure follows the use of a standardized worst case fire (as per ISO 834) as the thermal load on the structure and the verification that individual structural elements do not reach a predefined critical temperature. Given that the temperature increase is directly associated to the thermal mass of the structural element, slim optimized structural elements generally will require thicker fire proofing. Furthermore, single element testing does not take on account optimised load redistribution or the thermo-mechanical behaviour of structural systems, therefore the same level of thermal protection will be provided for critical and non-critical structural elements (or sectors). The result is most likely a structural system that, when it comes to fire behaviour, is most likely over dimensioned where it is not necessary and under dimensioned when it is critical. Both outcomes are inconsistent with the objectives of optimization. This paper presents a framework that enables the introduction of structural fire behaviour into a unique optimization process that delivers a comprehensively optimized structure. This framework addresses the development of realistic fires within specific structures, proper assessment of material property evolution with temperature, adequate utilization of thermo-mechanical models to assess structural performance and the proper definition of failure criteria.