What happened at the Broadgate Development, London?

In 1990 a fire developed at the partially complete 14-level multi-storey Broadgate Development.

The fire grew with temperatures estimated at around 1,000°c. Structural steel is estimated to become elastic at around 600°c and some beams were deformed, however no structural failure occurred and the integrity of the floor slabs was maintained (they were constructed using longspan lattice trusses and beams supporting concrete slabs).

The estimated cost of the damage was around £25m.

What caused the Broadgate Development fire?

The source of ignition is unknown, however the building construction was incomplete, so it did not contain any passive fire protection to the steelwork. The sprinkler systems and other active measures were not yet commissioned and not in operation.

What can the industry learn from the Broadgate Development incident?

Following the fire it was observed that no connections had failed, but there were deformations of bolt holes and broken bolt heads. Some of the connection plates had fractured along the length of their beams, but had still managed to transfer shear appropriately.

Various levels of deformation were observed in the support structures which were due to tensile forces induced during cooling.

Structural analysis later proved that fire protection for structural elements can be over-specified and are not required as much as once thought; fire engineering principles can be applied to reduce the cost of fire protection and therefore the cost of construction.

This became a catalyst for steel companies to carry out research in order to gain an economical benefit. The research has shown that the inherent fire resistance of this common structural framing system is far greater than is demonstrated using standard fire tests.

In larger-scale fire tests conducted at the Cardington test facility it was shown that unprotected beams which would fail within 20 minutes for a simply supported structure using a standard fire test could in fact survive, offering more than one hour of fire resistance.

This finding now underpins much of modern structural fire engineering.