Developments in fire-safe design - Steel Structures.

In the mid 1990s, a series of realistic fire tests were carried out on a full-sized eight-storey steel-framed building at the Building Research Establishment’s large-scale test facility at Cardington, Bedfordshire (see Fig. 34.8). Full analysis of the test results has shown that the behaviour of steel members in a whole building frame with all of the restraint, continuity and interaction that can occur is very different from the behaviour of single members in unrestrained standard fire tests. Columns will need protection because deformation of columns can cause damage beyond the compartment of fire origin, but unprotected composite beams were able to survive a temperature of 1100°C without collapse (see Fig. 34.9). It became clear that mem- brane action in the composite slab was responsible for the observed high performance and that it would be possible to design steel-framed buildings in such a way as to allow the beams to remain unprotected.

Realistic fire tests in a modern steel-framed office building showed that stability requirements can be maintained without beam protection
Fig. 34.8 Realistic fire tests in a modern steel-framed office building showed that stability
requirements can be maintained without beam protection
A further floor test was conducted at BRE’s Garston laboratory to quantify the effect of tensile membrane action, and Bailey and Moore  showed that the strength and location of the reinforcement in a composite slab and the aspect ratio of the slab panel itself largely govern its load capacity.

This analysis has been incorporated into simple design guidance by the UK Steel Construction Institute (Newman et al.), which allows secondary beams to remain unprotected in composite slab panels up to 9 metre span for fire ratings up to 60 minutes. These limitations may be extended by use of the Bailey and Moore calculation method from first principles or by application of a specialized finite element program such as VULCAN, which is adapted to deal with fire conditions.

Unprotected beams were heated to 1100°C without collapse
Fig. 34.9 Unprotected beams were heated to 1100°C without collapse

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