Business Weekly : Zero grounds for Ground Zero conspiracy theory

Zero grounds for Ground Zero conspiracy theory

by Sam Fountain | Business Weekly | September 14, 2007

Conspiracy theories surrounding the World Trade Centre disaster have been countered by a new mathematical analysis of the phenomenon by a Cambridge University academic.

Dr Keith Seffen, senior lecturer in the structures group in the Department of Engineering, has published a paper which draws on established engineering models to demonstrate that the collapse sequence of the Twin Towers following the terrorist strike was "quite ordinary and natural."

The report, which is due to be published in the American Society of Civil Engineers' Journal of Engineering Mechanics, further deflates the speculation that continues to surround the catastrophe, focusing on the seemingly orderly manner in which both of the towers collapsed.

Despite the fact that the causes behind the rapid collapse of both structures are now well understood, conspiracy theories claiming insider knowledge stretching to the very top of US government continues to rage.

Dr Seffen was inspired to investigate the collapse in an effort to afford some closure to the debate and to unearth scientific proof that the way in which the buildings fell was a normal response to the stresses they were exposed to.

"I thought immediately that there had to be a rational explanation for why the collapse happened as it did -- one which draws on engineering principles," said Seffen.

"After searching the current literature, it became clear that many studies focused on the phase just before collapse settles in."

"They rightly show that the combination of fire and impact damage severely impaired those parts of the building close to where the aircraft hit to hold the weight of the building above."

"The top parts were bound to fall down, but it was not clear why the undamaged building should have offered little resistance to these falling parts.

Dr Seffen defined 'the residual capacity' of the building, and used this calculation to develop a dynamic model of the sequential collapse of the successive levels of the buildings.

Using this model, Seffen then simulated the successive squashing, or 'pancaking' of individual storeys based on the residual capacity already identified.

Previous studies into progressive collapse and propagating instabilities have identified the pancaking process, but it usually affects structures such as undersea pipelines, rather than buildings.

Seffen used his calculations to predict that the limited residual capacity of the buildings -- caused by the impact of the two planes -- would have caused them to fall down completely within 10 seconds of the start of the collapsing sequence.

He showed that the mechanics of the pancaking were consistent with the dual impact of the planes, although it was similar to the process in a controlled demolition, except that it ran in the opposite direction.

"In all senses, the collapse sequence was quite ordinary and natural. The World Trade Centre Towers were designed to absorb an aircraft impact, but an accidental one with much less fuel and speed," he said.

"It is widely acknowledged that the impacts of September 11 were extraordinary, which led to consequences well in excess of the design capacity for the buildings.

"The original design of both towers must be praised for standing as long as they did, saving more lives than might have been expected.

"The aim was to produce a credible scientific explanation for the totality of the collapse once it began."