2 January 2018
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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.
Most structures in Europe are constructed using limit state design methods. Most of these structures are protected against some form of specified fire scenario. However, only a small minority of projects link these two major considerations together to form part of a unified structural fire design process. The Eurocodes provide designers with the necessary procedures to undertake an accurate and economical structural fire design, yet few engineers ever consider undertaking such an assessment. This article will focus on the load actions and combinations to be considered that enable the engineer to perform an adequate structural assessment for the accidental limit state in fire. It will also cover important considerations to ensure that any structural fire engineering strategy is appropriately aligned, and the key information is available within the contract chain to facilitate this performance-based 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.