Behavior of structures in fire and real design - A case study

A great deal of work on the behavior of composite steel-concrete structures in fire has been developed since the Cardington frame fire tests (UK) conducted in the 1990s. This has now been broadened so that the design of structures to resist fire 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 behavior in fire. Since the collapse of the World Trade Center in New York City in 2001 (9/11), robust engineering solutions incorporating the response of a building to fire are in great demand. The basics of structural mechanics at high temperatures can be used in such designs to understand the fire response of many structures with the aid of computer modeling. This article provides a direct comparison between the structural response of an eleven-story office building in the city of London, when designed in a prescriptive manner with applied fire protection on all 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 a fire can be maintained in specific cases without relying on passive fire protection. This study contributes to the field of structural fire engineering by extending the research work previously conducted by the author 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 a 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 upon among the necessary stakeholders in this project. © 2006 Society of Fire Protection Engineers.