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Cardington test data could propel industry forward

NEWS - What can a re-opened Cardington research facility achieve?

MASSIVE INCREASES in computing power and detailed worldwide research mean that structural engineers have the opportunity to analyse structures as a whole.

They no longer need to be considered as a series of individual elements that just happen to be linked together into a building.

Whole building response to normal live loads can now be assessed with incredible accuracy. Structures can be designed to combine strength and economy without compromising safety. But when it comes to structural response to extreme events, such as fire, blast and impact, the situation is less rosy.

However beguiling a computer simulation of fire development and structural response may be, its depiction of reality is only reliable if it can be validated against relevant experimental data.

The mountain of data that came out of Cardington during the late 1990s has validated many models - but as time passes and clients' needs develop that data is becoming increasingly inadequate.

NCE's formal urvey of leading academics, fire engineers and special interest groups has uncovered a long shopping list of additional research now considered to be vital to the development of the construction industry, in the UK and worldwide.

These mostly relate to the commercial pressures which are pushing designers towards using longer spans, thinner floors and faster construction, often using prefabricated modules.

Spans in the range of 12m to 18m are now commonplace in commercial office development. At the moment there is absolutely no data on how steel or concrete frames on this scale will react to a typical office blaze. The Cardington data is derived mostly from tests on the steel frame building, but its spans were less than 10m.

Extrapolating data from the shorter spans for longer span structures is an exercise that has to be undertaken with caution.

There was near-universal agreement that full scale research into the fire performance of long span frames would be the top priority if Cardington reopened. Almost as pressing is the perceived need for evaluation of the fire performance of the concrete floors these frames support, be they flat slab, composite, post tensioned, normally reinforced or precast hollow core units.

The rst series of Cardington tests revealed the hitherto unappreciated importance of the thermal expansion of the structure during a major fire. This becomes increasingly relevant as span lengths increase. And as spans and potential thermal expansion increase, joint performance becomes critical.

Despite their obvious importance, joints have rarely been tested at full scale under realistic conditions. Nor has the behaviour of cladding on the building. Recent major fires, such as the one at Basingstoke in 1991, have shown how cladding performance can have a direct effect on the rate of fire spread and the peak temperatures reached between the floors.

There was only limited cladding testing at Cardington first time around, but many would like to see a thorough investigation of how the details of fixings and fire stopping react in real infernos. Others hope for tests on the stability of compartmentation, the integrity of lift shafts and power supply, and fire protection for lifts as a means of escape.

Some pointed to an 'extreme event' test already carried out at Cardington.

Towards the end of the research on the facility's concrete building one corner column was cut through to simulate the effect of a lorry strike or similar.

The building performed very well. But how would similar structures react to a combination of extreme events, such as an internal explosion which took out structural members and triggered a major fire?

Post 7/7 such a scenario has to be considered, and Cardington is the only place where realistic research could be carried out.

Dave Parker Find out more about the campaign to reopen Cardington at the NCE stand at Civils 2005

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