New Concepts in Structural Strength Assessment for Large Buildings in Fire

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by Susan Lamont,
Asif Usmani,
Michael Rotter,
Barbara Lane,

Document Type: Proceeding Paper

Part of: Structures 2001: A Structural Engineering Odyssey

Abstract: This paper presents theoretical descriptions of the key phenomena that govern the behaviour of composite framed structures in fire. These descriptions have been developed in parallel with large-scale computational work undertaken as part of a research project [University of Edinburgh, 2000] to model the full-scale fire tests on a composite steel framed structure at Cardington (UK) [Bravery, 1993]. Behaviour of composite structures in fire has long been understood to be dominated by the effects of strength loss caused by thermal degradation and that large deflections and runaway resulting from the action of imposed loading on a weakened structure. Thus strength and loads are quite generally believed to be the key factors determining structural response (fundamentally no different from ambient behavior). The new understanding produced from the aforementioned project [University of Edinburgh, 2000] is that, composite framed structures of the type tested at Cardington possess enormous reserves of strength through adopting large displacement configurations. Furthermore, it is thermally induced forces and displacements, not material degradation that govern the structural response in fire. Degradation (such as steel yielding and buckling) can even be helpful in developing the large displacement load carrying modes safely. This of course is only true until just before failure when material degradation and loads begin to dominate the behaviour once again. All analytical expressions developed in this paper have been developed ab-initio from fundamental structural mechanics.

Subject Headings: Composite structures | Chemical degradation | Fires | Structural strength | Load factors | Thermal properties |

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