September 10, 2008

Scientists Seek Stronger Steel For New Skyscrapers

Scientists are currently seeking to develop new stronger steel in light of recent findings that show weakness in steel due to its magnetic properties.

Dr Sergei Dudarev, principal scientist at the United Kingdom Atomic Energy Authority (UKAEA) told the British Association Science Festival that the Twin Towers in New York City fell because their steel backbones lost strength in the fires that resulted from the plane impacts.

Their discovery marks the first time that experts have identified one of the primary causes of the towers' collapse on September 11, 2001.

Tiny irregularities in steel's structure can disrupt its internal magnetic fields, causing it to become weak and rigid in high temperatures.

"Steels melt at about 1,150C (2,102F), but lose strength at much lower temperatures," explained Dr Dudarev.

"[The steel] becomes very soft. It is not melting but the effect is the same," he said.

Dudarev pointed to the work of blacksmiths who had profited from this feature of steel by using it to become more pliable at temperatures lower than its melting point.

The peak in this pliability is at 911.5C, but begins at much lower temperatures, at around 500C (932F) - a temperature often reached during building fires.

The new findings are published in two papers by researchers from UKAEA's nuclear fusion laboratory at Culham near Oxford, UK

"Understanding how materials behave means we can find the right "Ëœmedicine' to make steel stronger at high temperatures. I thought the Twin Tower structures might be a useful comparison for the fusion data. But I was surprised to find that the graphs showing the weakening of steel fitted almost exactly," said Dr Dudarev.

It is likely that steel within the Twin Towers reached temperatures close to this. The fire mid-way up the building heated the steel struts caused the structure to become more elastic and collapse under the weight of the floors above.

UKAEA has helped pioneer fusion power - deriving energy by forcing together atomic nuclei - at Europe's JET lab in Oxfordshire; and is now assisting the development work on the world first large-scale experimental reactor known as Iter.

The extended periods over which Iter will run means the reactor must have robust materials built into the vessel where the fusion reactions will occur.

Dr Dudarev said it should be possible to tune the properties of suitable new steels by adding a mix of other elements.

With ever taller skyscrapers being planned "“ the latest being the Mile-High Tower in Saudi Arabia "“ the information could help develop steels and alloys which can withstand the high temperatures that occurred in the Twin Towers fire, the UKAEA said.

"We need to look at the magnetic properties of steel, [and] vary their chemical composition in a systematic way in order to get rid of this behavior," he said.


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