The structural behaviour of steel frames with composite floorslabs subject to fire: Part 1: Theory

This paper presents the development of a new design method for calculating the performance of steel framed buildings, with composite flooring systems, subject to fire. This design method is based on the results from a series of full-scale fire tests on an eight-storey steel framed building, together with associated theoretical and further experimental investigations. The results from this work show that the performance of composite steel deck flooring systems in fire is under-utilised in current design procedures. This is owing mainly to the ability of lightly reinforced composite slabs to bridge over the supporting fire-damaged steel beams and transfer load, using membrane action, to the undamaged parts of the steel structure. From these observations a simple design method is developed that is based on a holistic, rather than an elemental, approach. This allows the various interactions between the components of a composite slab, supported by a grillage of steel beams, to be taken into account, producing cheaper and more innovative, site-specific, fire-engineering solutions. A companion paper shows how this design method can be applied to practical buildings.