Author: K. J. LaMalva (Simpson Gumpertz & Heger Inc)
2 January 2018
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K. J. LaMalva (Simpson Gumpertz & Heger Inc)
The only permitted alternative to standard fire resistance design is structural fire engineering (SFE), as constituted in the new Appendix E. SFE explicitly evaluates the demand and capacity of structural systems under fire loading in a similar manner as other design loads are treated in structural engineering practice.
Due to common misconceptions and lack of industry guidance, designers often erroneously intermingle these two approaches in order to justify structural fire protection variances. To combat this poor practice, recent industry efforts in the USA have focused on formally bifurcating these two design options, and providing specific requirements for the SFE approach.
The Grenfell Tower tragedy in London last June was a stark reminder of how rapidly a fire can spread and the horror which it can cause. In the wake of this disaster, the UK construction industry is actively examining what can be done to minimise the risk of similar tragedies in the future. It is likely that one of the recommendations will be a clearer identification of responsibilities, but whatever the outcome it will clearly be helpful for all members of the design team to have a good understanding of all aspects of fire safety, as well as detailed knowledge about those aspects under their direct control.
All the articles from the January 2018 issue.
Performance-based structural fire design can play an important part in delivering iconic buildings. Early design team engagement with critical issues, including fire safety considerations, allows a holistic solution to be developed, in contrast to post-applied fire engineering which could severely compromise the original design intent. Four Pancras Square (London) is a successful example of where early fire engineering engagement has helped deliver an iconic design. The building features an external, fully load-bearing, weathering steel frame, with a storey-deep Vierendeel transfer truss. To allow the weathering steel to develop its protective patina and achieve the desired aesthetic, it must be left untreated and exposed; this is in conflict with traditional fire resistance solutions. This paper documents the key steps undertaken in realising the building and describes how they were tackled at the interface of the fire and structural engineering disciplines. These include quantification of the design goals, selection of the fire constraints, understanding the behaviour of unconventional steel, quantifying thermal exposure for external elements and, finally, quantification of structural response in fire.