Researchers at Manchester and Edinburgh Universities will begin studying the cooling stage of building fires early next year to determine why steel and concrete connections continue to fracture hours and days after the flames have been extinguished.
The outcome could improve the safety of firefighters and the public in the proximity of buildings that have recently been ablaze.
Those involved in the three-year project, led by Prof Colin Bailey of the Mechanical, Aerospace and Civil Engineering Department at Manchester will observe the behaviour of steel-concrete composite structures subjected to different axial restraint conditions and natural fire scenarios.
The Anglo-Dutch steel giant Corus, one of the project’s partners, will keep an overview of the practical applications of the study’s findings.
‘This research will allow us to look at the full story to make sure we can analyse from the start of the fire to the cooling phase,’ said John Dowling, head of the fire protection and engineering department at Corus. ‘We have a commitment in the steel industry to leave no stone unturned. We should not take chances.’
The research is part of a larger series of projects, which began in the early 1990s, on the behaviour of building structures during fires. Between 1994 and 1996 British Steel (now Corus) carried out a series of six large-scale fire tests on an eight-storey composite building with metal deck floors at the Building Research Establishment test facility at Cardington in Bedfordshire.
Time and effort
‘This test mainly looked at what happens during the heating phase of a fire,’ said Dowling. ‘We didn’t particularly put a lot of time and effort into what happens in the cooling stage. But the number of things that happened, such as failure of connections, did cause a few people to pause and say, “We need to look at this as well for the sake of completeness”.’
According to Bailey, Manchester researchers will conduct their experiments on steel-concrete composite slabs measuring eight metres long and 1.5 metres wide.
Using a gas fire, the slabs will be heated at temperatures ranging between 800 and 1,200ºC. Then they will be cooled down to 20ºC.
The internal push-and-pull forces of the slabs will be measured on the ends with load cells, jacks and strain gages.
Meanwhile, Edinburgh researchers will use the measurements derived by the experiments and work them into numerical models that will simulate structural behaviour during the cooling phase.
Those involved in the project hope the outcome will lead to better performance-based design codes for buildings in the UK.
‘In England and Wales in particular, the building regulations are couched in functional terms,’ said Dowling. ‘In other words, they tell you what you must do, but not how you do it.’
‘As an example,’ he added, ‘the building regulations will contain a statement, such as “in the event of a fire the building must retain its stability for a reasonable period”. The regulations will not tell you what a reasonable period is.’
Dowling said the government does publish ‘prescriptive documents’, which gives suggestions on how to construct a building to code, but they do not take into account the ‘actual behaviour of the building’.
‘When looking at a performance-based approach, you have to look at how a building behaves over the lifetime of a fire,’ he said. ‘When dealing with large and complex buildings in particular, this is very much the right approach to use because you’re not relying on the blanket provision of a book that tries to be a catch-all answer. You are designing a particular solution for a particular building.’
Bailey said he expects the results of the first set of cooling phase tests to come out within eight months. Following that will be another series of tests, which will allow the researchers to benchmark the models.
The project due to begin in February next year and to end in January 2010 has received funding via a £310,000 grant from the EPSRC.
In addition to Corus, Bailey said global consulting engineering firm Arup is adding significant professional guidance to the project.
‘Arup is a leading consultant in fire design so it will steer us to make sure that what we get out of the end of this project is of practical use to the industry,’ he said.
Researchers will begin studying the cooling stage of building fires early next year to determine why steel and concrete connections continue to fracture after the flames have been extinguished.