Behavior of Structures in Fire and Real Design - A Case Study

Abstract

A great deal of understanding into the behaviour of composite steel-concrete structures in fire has been developed since the Cardington frame fire tests (UK) 1990s. This has now been broadened so that structures in fire design has a real engineering basis and is not reliant on results from single element testing in the standard furnace. Several projects involving office buildings in the UK and abroad have highlighted the need for developing the understanding of whole frame behaviour in fire. Since 9-11 robust engineering solutions where the response of the building to an event like fire is known are in great demand. The basics of structural mechanics at high temperatures can be used in design to understand many structures with the aid of computer modelling. This paper provides a direct comparison between the structural response of an 11-storey office building now constructed in the city of London, when designed in a prescriptive manner, with applied fire protection on all the load bearing steelwork, and the response of the same structure designed using a performance based approach leaving the majority of secondary steelwork unprotected. The intent is to demonstrate that structural stability during the fire limit state can be maintained in specific cases without relying on passive fire protection. This paper contributes to the field of structural fire engineering by extending the research work previously conducted by the authors1 to a real design case and addresses the issues raised by approving authorities, insurers and the client when a fire engineered approach is used to calculate structural response to fire. It also demonstrates the use of advanced analysis to understand beam-core connection response in fire, as part of a series of global finite element analyses to ensure that the unprotected structure proposed provides structural stability and maintains compartmentation for the design fires agreed with the necessary stakeholders in this project.