Aircraft impact Design for Twin Towers

Picard

New Member
I was reading on Wikipedia about the design for the Towers. It said the following " In designing the World Trade Center, Leslie Robertson considered the scenario of the impact of a jet airliner, the Boeing 707, which might be lost in the fog, seeking to land at JFK or at Newark airports ".

Does anyone have documentation to indicate this ? I'm inclined to believe it, as no building can withstand an impact from a plane traveling at high speed and full of fuel. Just look @ the pentagon for example.
 
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deirdre

Senior Member.
NIST says ( I added bold emphasis)
5.3.2 Aircraft Impact The accidental 1945 collision of a B-25 aircraft with the Empire State Building sensitized designers of high-rise buildings to the potential hazards of such an event. However, building codes did not then, and do not currently, require that a building withstand the impact of a fuel-laden commercial jetliner. A Port Authority document indicated that the impact of a Boeing 707 aircraft flying at 600 mph was analyzed during the design stage of the WTC towers. However, the investigators were unable to locate any documentation of the criteria and method used in the impact analysis and were thus unable to verify the assertion that "...such collision would result in only local damage which could not cause collapse or substantial damage to the building and would not endanger the lives and safety of occupants not in the immediate area of impact." 8
Since the ability for rigorous simulation of the aircraft impact and of the ensuing fires are recent developments and since the approach to structural modeling was developed for this Investigation, the technical capability available to The Port Authority and its consultants and contractors to perform such an analysis in the 1 960s would have been quite limited.


8 Letter with an attachment dated November 13, 2003, from John R. Dragonette (Retired Project Administrator, Physical Facilities Division, World Trade Department) to Saroj Bhol (Engineering Department, PANYNJ).
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page 55 https://nvlpubs.nist.gov/nistpubs/Legacy/NCSTAR/ncstar1.pdf
 

Picard

New Member
I heard about that, and I find it hard to believe they could design the building to take that sort of impact. Not even the pentagon, which is reinforced was able to hold up to an impact.
 

Mendel

Senior Member.
I'm inclined to believe it, as no building can withstand an impact from a plane traveling at high speed and full of fuel.
The WTC withstood the impact for hours an hour as is. Mechanically, the engineering was sound. What brought it down were the fires.

If an analysis was done, it might not have considered the consequences that this kind of fire might have. A "seeking to land" airliner would not be "full of fuel", as it would be near the end of their journey.
 
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deirdre

Senior Member.
Not even the pentagon, which is reinforced was able to hold up to an impact.

the Pentagon didn't collapse. there was just a big hole, like the Twin towers.

One World Trade Center (WTC 1) the "North Tower" was hit at 8:46 a.m. Eastern time and collapsed at 10:28 a.m. Two World Trade Center (WTC 2) the "South Tower" was hit at 9:02 a.m. and collapsed at 9:59 a.m.
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Keith Beachy

Senior Member
The structural engineer designed the tower for an impact of a 707 lost in the fog trying to land, it would be at 180 to 200 mph.

LESLIE E. ROBERTSON -
The two towers were the first structures outside of the military and nuclear industries designed to resist the impact of a jet airliner, the Boeing 707. It was assumed that the jetliner would be lost in the fog, seeking to land at JFK or at Newark. To the best of our knowledge, little was known about the effects of a fire from such an aircraft, and no designs were prepared for that circumstance. Indeed, at that time, no fireproofing systems were available to control the effects of such fires. https://www.nae.edu/7480/ReflectionsontheWorldTradeCenter

LESLIE E. ROBERTSON -
It appears that about 25,000 people safely exited the buildings, almost all of them from below the impact floors; almost everyone above the impact floors perished, either from the impact and fire or from the subsequent collapse. The structures of the buildings were heroic in some ways but less so in others. The buildings survived the impact of the Boeing 767 aircraft, an impact very much greater than had been contemplated in our design (a slow-flying Boeing 707 lost in the fog and seeking a landing field). Therefore, the robustness of the towers was exemplary. At the same time, the fires raging in the inner reaches of the buildings undermined their strength. In time, the unimaginable happened . . . wounded by the impact of the aircraft and bleeding from the fires, both of the towers of the World Trade Center collapsed. https://www.nae.edu/Publications/Br...ecurity/ReflectionsontheWorldTradeCenter.aspx

To add to the speculation there was a "white paper" (a marketing device) by the Port Authority to brag about the WTC towers, and it had a 707 at 600 mph... I think Robertson wanted to stop the 707 at the shell. With the planes on 9/11 going 470 and 590 mph, they broke the shell. The buildings did not collapse due to the impacts. This was an issue since a plane had hit the Empire State Building. There was no study of an impact at 600 mph - it appears to be Port Authority marketing, not an engineering study.

At 180 mph the shell of the WTC would stop the aircraft at the shell. There was a study after 9/11 of what it would take to break the shell, and what thickness of steel could stop the 590 mph impact... Have to look it up -

The most likely accident with an aircraft and building would be lost in the fog low on fuel trying to land. If the pilot had full fuel he would (if he had any judgement) climb to VFR (clear sky) and find suitable landing field.

Found the paper... I have a copy on a computer at home.
A numerical simulation of the aircraft impact into the exterior columns of the World Trade Center (WTC) was done using LS-DYNA. For simplification, the fuselage was modeled as a thin-walled cylinder, the wings were modeled as box beams with a fuel pocket, and the engines were represented as rigid cylinders. The exterior columns of the WTC were represented as box beams. Actual masses, material properties and dimensions of the Boeing 767 aircraft and the exterior columns of the WTC were used in this analysis. It was found that about 46% of the initial kinetic energy of the aircraft was used to damage columns. The minimum impact velocity of the aircraft to just penetrate the exterior columns would be 130m∕s. It was also found that a Boeing 767 traveling at top speed would not penetrate exterior columns of the WTC if the columns were thicker than 20mm. https://ascelibrary.org/doi/10.1061/(ASCE)0733-9399(2005)131:10(1066)
 
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Dingo

Member
I don't see that claim anywhere on the current Wikipedia page for the World Trade Center.

And saying "... no building can withstand an impact from a plane traveling at high speed and full of fuel ..." is vague and probably overly broad. Absolutes rarely exist without exceptions. For instance, in 1945 a B-25 bomber crashed into the Empire State Building and it survived.

This one has been analysed to death. The key difference being that the B-25 was comparitively small and slow. The maximum speed of a B-25 is 272mph, for instance, which makes a huge difference in the kinetic energy.

Absolutely agree that the statement is uselessly vague, haha.
 

Oystein

Senior Member
The best accounting of the Port Authority's study of a 707 impact at 600 mph can be found in James Glanz's book "City in the Sky". I found it first in this 2011 post at the JREF forum by user "tfk":
http://www.internationalskeptics.com/forums/showthread.php?p=6993609#post6993609

Earlier this year, I read the book myself, I have a copy, and checked that the quotes and page numbers given by tfk are correct. Here are the technical excepts from Glanz's book as far as tfk has them:
The first part of the calculation would have been quite simple. The towers had been designed to withstand the forces of windstorms with gusts of at least 120 miles an hour. Specifically, they were supposed to hold up against at Least forty-five pounds of lateral force on every square foot without shearing off and toppling. Each tower would be about 1,350 feet tall and 209 feet across on each face: 282,150 square feet. So if a wind sufficient to exert forty-five pounds per square foot of force was blowing directly against one of the faces. that would be about 13 million pounds. all told. And the tower should stand, with a standard safety margin of perhaps 30 to 40 percent to spare.

To figure out if the plane had a chance of tipping the tower over. Mal Levy’s engineers needed to estimate how much force the collision might produce. A Boeing 707 made a B-25 look like an insect in comparison. With a tip-to-tip wingspan of 131 feet and a fuel capacity of more than twenty thousand gallons. a fully loaded 707 can weigh 300,000 pounds on takeoff, and its cruising speed is about 600 miles per hour. The engineers knew that parts of the little B-25 flew all the way through the limestone-encased Empire State Building and out the other side. So it might have been reasonable to assume that the bigger. faster 707. after plowing into the much more compliant facade of a World Trade Center tower, would not come to a complete stop before it reached the opposite side of the floor, 209 feet away. It is a complicated problem to figure out precisely how hard the plane might push on the tower during a collision, but given the plane’s known weight. initial speed, and stopping distance, any freshman engineering student could come up with a rough estimate. The number turns out to be 17 million pounds, probably within the safety margin.

Levy’s engineers had discovered that not even a speeding 707 would shear off one of the towers.
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In the book, the story is layed out on pages 131 thru about 139.
I think it is best if you read tfk's full post for context and explanation.
 

Mendel

Senior Member.
More from the forum post that Oystein cites:
Article:
The second calculation imagined that a number of the beams on one side of the building, equivalent to the wingspan of the plane, were "surgically removed". As if you just took a Sawzall & cut them out. Absolutely no other damage to any part of the building. No fires, no damaged core columns, no damaged floors, etc.

The question asked: Would the building fall over under this condition.

They found out that it would not.

Clearly, neither one of these very unrealistic & very crude calculations comes anywhere CLOSE to a rigorous analysis upon which one could make the assertion that the building "was designed to withstand a jet impact".

So, yes, a crude (?) impact analysis, but no postcrash considerations, it seems.
 
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