Abstract for peer-review
SiF'08, Singapore, 28-30 May, 2008
The reliability of structures in fire
David Lange, Asif S. Usmani, and Jose Torero
BRE Centre for Fire Safety Engineering, Institute for Infrastructure and the Environment, AlexanderGrahamBellBuilding, The KingsBuildings, The University of Edinburgh
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Abstract
Structural fire engineering has been benefiting for some time from a growing understanding of the fundamental mechanics that govern the behaviour of structures under thermal effects. As the field of fire engineering moves from a prescriptive to a performance based approach, this growing understanding is being used with growing confidence by engineers to develop new design solutions for structures and to justify the implementation of rational fire safe designs without the need for expensive passive fire protection. However, unlike ambient, or static, design situations, the application of these methods ismade without consideration of the reliability of the resulting solution. More often than not, a fire-engineered solution is a deterministic application of fundamental mechanics to a specific thermal and static loadingcombination, consisting of a ‘design fire’ and some factored mechanical loading. As a result, safety of the final design can only beguaranteed via the implementation of intentionally conservative assumptions that result in some undetermined and unknown safety factor in the system. These solutions are applied in an ad-hoc manner to areas of perceived high risk.
The current Eurocodes present a design framework which is based upon the First Order Reliability Method, and the targets of the Eurocodes are based upon indices of Safety or Reliability. The reliability of a system (or component) is a measure of the probability that the load on the system will be less than the systems resistance. This concept is the basis for the partial safety factors which are prevalent throughout design codes worldwide, and it therefore seems only natural to apply it to structural fire safety design.
By taking account of alternative, thermally enhanced load carrying mechanisms, and using stochastic methods to model fire scenarios this paper addresses the application of reliability methods to structural fire engineering, for both protected and unprotected components. A solution is provided that allows for a performance based approach to structural fire engineering that can be calibrated to conform with current and future Eurocode reliability targets, irrespective of the methods which are used to model either the fire or the structure.
Keywords: Performance based design, reliability, design methodology