A NEW METHOD TO DETERMINE THE ULTIMATE LOAD CAPACITY OF COMPOSITE FLOORS IN FIRE

摘要

This paper presents a new method for determining the ultimate load capacity of composite floors systems in multi-storey building fires. Collapses of composite frame buildings in fire are an extremely rare event (event of September 11, 2001 were clearly extraordinary), therefore the manner of structural failure is not well understood. One of the main contributions to the robust performance of such structures is due to the tensile membrane mechanism in the composite deck slab. The research group at Edinburgh has discovered that the development of tensile membrane mechanism in fire is much more reliable relative to ambient conditions. This is because a large amount of thermal strain allows composite floor systems to assume highly deflected shapes while limiting the magnitude of damaging tensile mechanical strains, thereby retaining the ability to carry loads for much longer. Clearly, if the limits of the additional load capacity through the tensile membrane mechanism was reliably quantified, a powerful design tool would become available to engineers. Some previous work exists in this regard, but there are fundamental flaws in these approaches. Essentially these methods project ideas from tensile membrane behaviour at ambient temperature and do not take adequate account of the thermal response. This work introduces a new three-step method to analyse the ultimate capacity of laterally restrained composite floor slabs in fire.