Cost-optimization based target reliabilities for design of structures exposed to fire

Abstract

Adequacy of structural fire design in uncommon structures is conceptually ensured through cost-benefit analysis where the future costs are balanced against the benefits of safety investment. Cost-benefit analyses, however, are complicated and computationally challenging, and hence impractical for application to individual projects. To address this issue, design guidance proposes target reliability indices for normal design conditions, but no target reliability indices are defined for structural fire design. We revisit the background of the cost-optimization based approach underlying normal design target reliability indices then we extend this approach for the case of fire design of structures. We also propose a modified objective function for cost-optimization which simplifies the evaluation of target reliability indices and reduces the number of assumptions. The optimum safety level is expressed as a function of a new dimensionless variable named “Damage-to-investment indicator” (DII). The cost optimization approach is validated for the target reliability indices for normal design condition. The method is then applied for evaluating DII and the associated optimum reliability indices for fire-exposed structures. Two case studies are presented: (i) a one-way loaded reinforced concrete slab and (ii) a steel column under axial loading. This study thus provides a framework for deriving optimum (target) reliability index for structural fire design which can support the development of rational provisions in codes and standards.

Keywords

Target reliability / Cost optimization / Life-cycle cost / Structural fire engineering / Design code

Relevance to resilience

The performance of structures under fire events is a crucial component of the built environment's resilience. The contribution presents a lifetime cost-optimization framework for the design of structures exposed to fire. This framework adopts a risk-based approach that informs resilience by considering uncertainties related to the structural system's performance during a fire and the consequential losses. Through the examination of specific case studies, target reliability indices are suggested for structural fire design, ensuring that the achieved safety level is optimum from a cost-benefit perspective. Overall, designing structures for fire exposure based on risk contributes to the resilient design of buildings.

Declaration of competing interest

The authors declare that they are not aware of competing financial interests or personal relationships that could have influenced the work reported in this paper.

Acknowledgements

This research was funded by the Ghent University Special Research Fund under grant 01N01219 “Multi-objective societal optimization of structural fire safety investments for uncommon projects using advanced regression techniques”.

Supplementary materials

Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.rcns.2024.03.004.

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