Dr Keith Seffen's paper - "Progressive Collapse of the World Trade Centre: a Simple Analysis"
Dr Keith Seffen's paper is now available here -
"Progressive Collapse of the World Trade Centre: a Simple Analysis"
http://winterpatriot.pbwiki.com/f/seffen_simple_analysis.pdf
Having now read it, a few comments, focussing mainly on the applicability of the model developed in this paper.
The applicability problems are mainly the result of assumptions developed in the introduction. To quote from page one -
"Those factors responsible for the onset of collapse are now well established. Despite localised and substantial horizontal impacts by fuel-laden aircraft, both towers survived until the intense fire compromised the ability of the remaining, in-tact columns close to the aircraft impact zones to sustain the weight of the buildings above them. The subsequent near free-falling of these upper parts over the height of just one storey resulted in dynamical “over-loading” of the relatively undamaged lower columns by a factor of 30 compared to their static load capacity, according to Bazant and Zhou (2002).
We can also argue, I think, that it is not "well established", and is speculative and not evidence based. The same might be said about the "intense fires" and of the nature of the failure of the "in-tact columns". Even so, it is a big leap from there to the next sentence, "the subsequent near free-falling of these upper parts" - thus going from "compromised" to a presumed simultaneous disappearance of all the columns, just like that.
As often elsewhere in this paper, he then cites Bazant and Zhou, as the authority to cover an otherwise surprising conjecture. This fire-generated "freefall" is important though, because that is all they have available to provide the initial collapse energy.
Seffen goes on to say this of Bazant and Zhou -
"They argue that the storey immediately below bears the brunt in terms of a localised, plastic buckling of its columns, and they show that the commensurate dissipation cannot arrest the motion of the falling part, leading to a sustained collapse."
Gordon Ross has done the best debunking of Bazant and Zhou that I have seen so far. -
http://gordonssite.tripod.com/id1.html
Bazant and Zhou ignore the elastic deformations, and they only looked at the "storey immediately below", as if it was stood on the ground in isolation. Elastic deformations are the "springiness", which famously allowed the towers to sway in the wind, and which is characteristic of steel. Gordon Ross' analysis shows that this giant spring would have made a huge difference; and therefore the collapse would have been arrested with only minor buckling.
Seffen then gets on to his "propagating instabilities", page 2, saying, "damage accrues in a prescribed fashion following an initiation phase. Depending on the local collapse behaviour inveigled by the instability sweeping through the initially undamaged structure". Usually, it is normal in such cases to be able to point to some physical details, about the materials and the geometry, that allows this "instability" to propagate; but in this paper it is not developed beyond a series of floors being squashed.
Next, a rare comment that indicates the actual details of the collapses were ever studied. -
"It is also clear that both collapse modes were progressive, as indicated by film footage: there was the sound of each successive impact of floor upon floor and a matching sequence of lateral ejection of debris."
It is clear that he didn't notice that the top sections of the towers disintegrated first, into plumes of debris, before the collapse wave moved down the towers, thus totally invalidating their "freefall impact" idea as the power source to propagate the instability through the undamaged structure below.
See this photostudy of the collapses -
http://www.exodus2006.com/explosives.htm
and also Gordon Ross -
http://gordonssite.tripod.com/id2.html
I am also surprised he is saying "there was the sound of each successive impact of floor upon floor" since it doesn't seem that clear-cut, to me, particularly since some are heard just before the collapse. The video "911 Eyewitness" has a good study of this subject.
In the section titled "Progressive Instabilities", page 5, Dr Seffen gives another account of the collapse initiation -
"For both WTC towers, the distributed nature of the aircraft impact sites resulted in a reduced but uneven cross-sectional stiffness over several floors due to differing degrees of missing and deteriorating material.
As the most severely affected columns gave way at one level within the impact site, the upper parts fell onto an already weakened cross-section compared to the rest of the building further below.
The resulting impingement produced peak forces correctly identified by Bazant and Zhou (2002) to be far in excess of the design capacity of these columns and hence, above the expected value of “Pmax ” (Fig. 1) that could be reasonably carried by them, even if perfect and undamaged. These columns began to deform plastically, thereby seeding failure of this, next part of the structure."
This sounds almost reasonable, if you believe in the "intense fires", and sudden weakness in hot steel, and it sounds like the collapse would be strongly asymmetric. With a few more cites of Bazant and Zhou, in the next few paragraphs, this problem is avoided by having all columns, in the model, buckle in unison and in a one-dimensional and linear way.
Using this simplification, the mathematical model is then constructed, and by the end of page 7 we have a result from the model indicating that it only has a quarter of the usual static strength when hit by a progressive instability.
Interestingly, on page 8, he considers some other factors that might make the model seem unrealistic; including elastic buckling -
"The magnitude of this ratio can be very large, but elastic buckling of the relatively stocky WTC box columns is unlikely. Instead, Bazant and Zhou (2002) suggest that, more realistically, the columns fracture under very little bending immediately beyond the squash load, thereby removing the softening phase altogether in Fig.2. "
The only reason that the WTC columns can be regarded as "stocky" is because they are only looking at one floor at a time. In reality the columns were going from top to bottom, and this is where taking each floor in isolation is a false approximation. The extensive cross-bracing, within the structure is, another issue that is completely ignored by the model.
In the next section, titled Dynamical Model of Collapse, we have this -
"Lateral stability is not considered in view of the near vertical collapse of both WTC towers."
In other words, since both the towers collapsed completely vertically, there is no reason to consider why they might have gone asymmetric.
Also, we have -
"The building everywhere above this floor begins to accelerate downwards as a rigid undamaged body when, at time t = 0, it impinges on the floor and columns beneath, which are assumed to fail in the manner proposed in the previous section. The instability is formed as a level “crushing front”, its propagation is compatible with the uniform compression of successive storeys,"
A "rigid undamaged body" acts as a hammer and destroys the rest of the building, except as pointed out earlier, far from being rigid and undamaged, it can be seen to disintegrate into a plume of debris first. Therefore we know this mechanism being described did not happen, and the model takes no regard of the obvious loss of mass as the debris falls away. The way the model relies on the top section, the most lightly-built part, to behave as a rigid body while destroying the larger and most strongly-built section, is also worth considering.
On page 13, he says -
"Thus, it is entirely appropriate to move the study forward within the spirit of using Eqn 10 directly, for it is assumed primarily that dissipation is confined to quasi-static deformation in the columns and that the progressive nature of collapse demands a continuous mass entrainment."
It demands a "continuous mass entrainment" - unlike what was actually observed.
Then on page 14 -
"As argued in Bazant and Zhou (2002), it is likely that the uppermost parts of the WTC towers were falling freely due to an absence of column resistance in the first weakest storey"
I wonder if Dr Seffen considers it "likely" himself, or if he just modestly prefers the credit to go to Bazant and Zhou once again.
The model is then further developed, to finally produce graphs representing possible collapse times for the towers, had they suffered this type of collapse, against varying levels of resistance, from zero up to a point where the resistance would have arrested the collapse. This then allows the strength of the towers, against this type of progressive instability collapse, to be read off the graph by using the observed collapse times. There is no discussion about the variation of this figure between the two towers.
It would be interesting to see a computer simulation of the collapse described for the towers by this model - I am sure it would look most unlike what was actually seen.
I did wonder what real situation this model would in fact model. Two ideas have come to mind. A vertical stack of empty Coke-cans crushed by dropping a brick - provided those lateral instabilities were dealt with somehow. You can then calculate the downward speed of the brick crushing the tins.
Another is the Kung Fu exhibition stunt where somebody punches down through a stack of roof tiles. You can probably estimate the maximum number broken for various amounts of available continuous punch-force. Maybe not the most useful idea…
Dr Seffen's acknowledgements -
"The author is extremely grateful to two anonymous referees for insightful and supporting comments."
Showing posts with label Keith Seffen. Show all posts
Showing posts with label Keith Seffen. Show all posts
University of Cambridge : 9/11 "conspiracy" theories challenged by Cambridge research
Sunday, November 18, 2007
9/11 "conspiracy" theories challenged by Cambridge research
University of Cambridge > Engineering Department > News & Features
11 September 2007
A new mathematical analysis of the collapse of the World Trade Centre has been published by a Cambridge University academic, with results that challenge conspiracy theories surrounding the September 11th attacks.
The new paper, by Dr Keith Seffen, uses established engineering models to demonstrate that once the collapse of the twin towers began, it was destined to be rapid and total.
Although the causes that initiated the collapse of the twin towers are now well understood, engineers continue to speculate about the speed and totality with which the buildings were demolished during the fateful attacks.
Some have even dared to suggest that the catastrophic events that followed two planes being flown into the buildings were the result of a conspiracy that extended to the top of government itself.
Dr Seffen, a Senior Lecturer in the Structures Group in the Department of Engineering, was moved to find a scientific explanation for the collapse when he heard about reports of possible insider involvement. Claims of "controlled demolition" were being suggested, in order to explain the speed, uniformity and similarity between the collapses of both towers.
"I thought immediately that there had to be a rational explanation for why collapse happened as it did, one which draws on engineering principles," he said. "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's new analysis, which will be published in a forthcoming issue of the American Society of Civil Engineers' Journal of Engineering Mechanics, focuses on calculating the residual capacity of the building to resist the weight of the floors above under collapse conditions.
He then develops a dynamic model of the collapse sequence, which simulates the successive squashing, or "pan-caking" of individual storeys based on the residual capacity already identified. The process is already well known from other studies of progressive collapse, but usually applies to other structures such as undersea pipelines, rather than buildings.
This allowed Dr Seffen to predict that the residual capacity of both buildings was limited, and once collapse had started, it would take only 10 seconds for the building to go down - just a little longer than the free-falling of a coin dropped from the top of either tower.
"The aim was to produce a credible scientific explanation for the totality of collapse once it began," he said.
"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. It is widely acknowledged that the impacts on September 11th 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."
University of Cambridge > Engineering Department > News & Features
11 September 2007
A new mathematical analysis of the collapse of the World Trade Centre has been published by a Cambridge University academic, with results that challenge conspiracy theories surrounding the September 11th attacks.
The new paper, by Dr Keith Seffen, uses established engineering models to demonstrate that once the collapse of the twin towers began, it was destined to be rapid and total.
Although the causes that initiated the collapse of the twin towers are now well understood, engineers continue to speculate about the speed and totality with which the buildings were demolished during the fateful attacks.
Some have even dared to suggest that the catastrophic events that followed two planes being flown into the buildings were the result of a conspiracy that extended to the top of government itself.
Dr Seffen, a Senior Lecturer in the Structures Group in the Department of Engineering, was moved to find a scientific explanation for the collapse when he heard about reports of possible insider involvement. Claims of "controlled demolition" were being suggested, in order to explain the speed, uniformity and similarity between the collapses of both towers.
"I thought immediately that there had to be a rational explanation for why collapse happened as it did, one which draws on engineering principles," he said. "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's new analysis, which will be published in a forthcoming issue of the American Society of Civil Engineers' Journal of Engineering Mechanics, focuses on calculating the residual capacity of the building to resist the weight of the floors above under collapse conditions.
He then develops a dynamic model of the collapse sequence, which simulates the successive squashing, or "pan-caking" of individual storeys based on the residual capacity already identified. The process is already well known from other studies of progressive collapse, but usually applies to other structures such as undersea pipelines, rather than buildings.
This allowed Dr Seffen to predict that the residual capacity of both buildings was limited, and once collapse had started, it would take only 10 seconds for the building to go down - just a little longer than the free-falling of a coin dropped from the top of either tower.
"The aim was to produce a credible scientific explanation for the totality of collapse once it began," he said.
"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. It is widely acknowledged that the impacts on September 11th 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."
Physorg dot com : 9/11 'conspiracy' theories challenged by Cambridge research
Saturday, November 17, 2007
9/11 'conspiracy' theories challenged by Cambridge research
Published: 13:43 EST, September 11, 2007
A new mathematical analysis of the collapse of the World Trade Centre has been published by a Cambridge University academic, with results that challenge conspiracy theories surrounding the September 11th attacks.
The new paper, by Dr Keith Seffen, uses established engineering models to demonstrate that once the collapse of the twin towers began, it was destined to be rapid and total.
Although the causes that initiated the collapse of the twin towers are now well understood, engineers continue to speculate about the speed and totality with which the buildings were demolished during the fateful attacks.
Some have even dared to suggest that the catastrophic events that followed two planes being flown into the buildings were the result of a conspiracy that extended to the top of government itself.
Dr Seffen, a Senior Lecturer in the Structures Group in the Department of Engineering, was moved to find a scientific explanation for the collapse when he heard about reports of possible insider involvement. Claims of "controlled demolition" were being suggested, in order to explain the speed, uniformity and similarity between the collapses of both towers.
"I thought immediately that there had to be a rational explanation for why collapse happened as it did, one which draws on engineering principles," he said. "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's new analysis, which will be published in a forthcoming issue of the American Society of Civil Engineers' Journal of Engineering Mechanics, focuses on calculating the residual capacity of the building to resist the weight of the floors above under collapse conditions.
He then develops a dynamic model of the collapse sequence, which simulates the successive squashing, or "pan-caking" of individual storeys based on the residual capacity already identified. The process is already well known from other studies of progressive collapse, but usually applies to other structures such as undersea pipelines, rather than buildings.
This allowed Dr Seffen to predict that the residual capacity of both buildings was limited, and once collapse had started, it would take only 10 seconds for the building to go down - just a little longer than the free-falling of a coin dropped from the top of either tower.
"The aim was to produce a credible scientific explanation for the totality of collapse once it began," he said.
"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. It is widely acknowledged that the impacts on September 11th 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."
Source: University of Cambridge
Published: 13:43 EST, September 11, 2007
A new mathematical analysis of the collapse of the World Trade Centre has been published by a Cambridge University academic, with results that challenge conspiracy theories surrounding the September 11th attacks.
The new paper, by Dr Keith Seffen, uses established engineering models to demonstrate that once the collapse of the twin towers began, it was destined to be rapid and total.
Although the causes that initiated the collapse of the twin towers are now well understood, engineers continue to speculate about the speed and totality with which the buildings were demolished during the fateful attacks.
Some have even dared to suggest that the catastrophic events that followed two planes being flown into the buildings were the result of a conspiracy that extended to the top of government itself.
Dr Seffen, a Senior Lecturer in the Structures Group in the Department of Engineering, was moved to find a scientific explanation for the collapse when he heard about reports of possible insider involvement. Claims of "controlled demolition" were being suggested, in order to explain the speed, uniformity and similarity between the collapses of both towers.
"I thought immediately that there had to be a rational explanation for why collapse happened as it did, one which draws on engineering principles," he said. "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's new analysis, which will be published in a forthcoming issue of the American Society of Civil Engineers' Journal of Engineering Mechanics, focuses on calculating the residual capacity of the building to resist the weight of the floors above under collapse conditions.
He then develops a dynamic model of the collapse sequence, which simulates the successive squashing, or "pan-caking" of individual storeys based on the residual capacity already identified. The process is already well known from other studies of progressive collapse, but usually applies to other structures such as undersea pipelines, rather than buildings.
This allowed Dr Seffen to predict that the residual capacity of both buildings was limited, and once collapse had started, it would take only 10 seconds for the building to go down - just a little longer than the free-falling of a coin dropped from the top of either tower.
"The aim was to produce a credible scientific explanation for the totality of collapse once it began," he said.
"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. It is widely acknowledged that the impacts on September 11th 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."
Source: University of Cambridge
Business Weekly : Zero grounds for Ground Zero conspiracy theory
Tuesday, November 06, 2007
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."
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."
New Kerala : Cambridge engineer challenges 9/11 demolition theory
Thursday, October 18, 2007
Cambridge engineer challenges 9/11 demolition theory
September 11, 2007
London, Sept.11 : A Cambridge University engineer has challenged the conspiracy theory surrounding the 9/11 attacks in the United States.
According to Dr Keith Seffen, once the collapse of the twin towers began, it was destined to be rapid and total.
Previous studies have tended to focus on the initial stages of collapse, showing that there was an initial, localised failure around the aircraft impact zones, and that this probably led to the progressive collapse of both structures.
One of many conspiracy theories suggests that the buildings came down in a manner consistent with a "controlled demolition".
Dr. Seffen's data says this is not needed to explain the way the towers fell and claimed the lives of over 2,800 people in New York.
Dr. Seffen says he was able to calculate the "residual capacity" of the undamaged building: that is, simply speaking, the ability of the undamaged structure to resist or comply with collapse.
His calculations suggest the residual capacity of the north and south towers was limited, and that once the collapse was set in motion, it would take only nine seconds for the building to go down.
Dr Seffen's research could help inform future building design. His findings are published in the Journal of Engineering Mechanics.
--- ANI
September 11, 2007
London, Sept.11 : A Cambridge University engineer has challenged the conspiracy theory surrounding the 9/11 attacks in the United States.
According to Dr Keith Seffen, once the collapse of the twin towers began, it was destined to be rapid and total.
Previous studies have tended to focus on the initial stages of collapse, showing that there was an initial, localised failure around the aircraft impact zones, and that this probably led to the progressive collapse of both structures.
One of many conspiracy theories suggests that the buildings came down in a manner consistent with a "controlled demolition".
Dr. Seffen's data says this is not needed to explain the way the towers fell and claimed the lives of over 2,800 people in New York.
Dr. Seffen says he was able to calculate the "residual capacity" of the undamaged building: that is, simply speaking, the ability of the undamaged structure to resist or comply with collapse.
His calculations suggest the residual capacity of the north and south towers was limited, and that once the collapse was set in motion, it would take only nine seconds for the building to go down.
Dr Seffen's research could help inform future building design. His findings are published in the Journal of Engineering Mechanics.
--- ANI
Guardian : Twin towers research refutes 9/11 conspiracy theories
Thursday, October 18, 2007
Twin towers research refutes 9/11 conspiracy theories
Anthea Lipsett | EducationGuardian.co.uk | September 11, 2007
A Cambridge University academic has shattered conspiracy theories surrounding the September 11 terrorist attacks that took place in New York six years ago today with a new mathematical analysis of the collapse of the World Trade Centre.
Keith Seffen, a senior lecturer in Cambridge's engineering department, used established engineering models to demonstrate that once the collapse of the twin towers began it was destined to be rapid and total.
While the causes that initiated the collapse of the towers are now well understood, engineers continue to speculate about the speed and totality with which the buildings were demolished during the fateful attacks.
Conspiracy theorists claim US government involvement in the catastrophic events that followed two planes being flown into the buildings. They suggest "controlled demolition" was the reason behind the speed, uniformity and similarity between the collapse of both towers.
But according to Dr Seffen's analysis of engineering principles, the way the towers collapsed 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 on September 11th 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."
Dr Seffen's research showed many studies focused on the phase just before collapse begins.
"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," he said.
His new analysis, which will be published in the American Society of Civil Engineers' Journal of Engineering Mechanics, calculates the average strength of a given storey of the building away from the impact area as it was being squashed flat.
This allowed him to define the "residual capacity" of the building, which he then used to develop a dynamic model of the collapse sequence, simulating the successive squashing of individual storeys based on the residual capacity already identified.
From this, Dr Seffen predicted that the residual capacity of both buildings was limited and once collapse had started it would take only 10 seconds for the building to go down.
This shows that the speed of the collapse as actually occurred was consistent with a "pancaking" effect caused by the dual impacts of the planes. As such, the mechanics of this pancaking process were exactly the same as a controlled demolition, but starting from the top and moving downwards, he said.
Anthea Lipsett | EducationGuardian.co.uk | September 11, 2007
A Cambridge University academic has shattered conspiracy theories surrounding the September 11 terrorist attacks that took place in New York six years ago today with a new mathematical analysis of the collapse of the World Trade Centre.
Keith Seffen, a senior lecturer in Cambridge's engineering department, used established engineering models to demonstrate that once the collapse of the twin towers began it was destined to be rapid and total.
While the causes that initiated the collapse of the towers are now well understood, engineers continue to speculate about the speed and totality with which the buildings were demolished during the fateful attacks.
Conspiracy theorists claim US government involvement in the catastrophic events that followed two planes being flown into the buildings. They suggest "controlled demolition" was the reason behind the speed, uniformity and similarity between the collapse of both towers.
But according to Dr Seffen's analysis of engineering principles, the way the towers collapsed 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 on September 11th 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."
Dr Seffen's research showed many studies focused on the phase just before collapse begins.
"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," he said.
His new analysis, which will be published in the American Society of Civil Engineers' Journal of Engineering Mechanics, calculates the average strength of a given storey of the building away from the impact area as it was being squashed flat.
This allowed him to define the "residual capacity" of the building, which he then used to develop a dynamic model of the collapse sequence, simulating the successive squashing of individual storeys based on the residual capacity already identified.
From this, Dr Seffen predicted that the residual capacity of both buildings was limited and once collapse had started it would take only 10 seconds for the building to go down.
This shows that the speed of the collapse as actually occurred was consistent with a "pancaking" effect caused by the dual impacts of the planes. As such, the mechanics of this pancaking process were exactly the same as a controlled demolition, but starting from the top and moving downwards, he said.
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