@parados,
Quote:I see you have ignored the fact that a large plane hit the building JTT.
Not at all, P. First we had to see that the fire issue was bogus. The fires were neither intense or long lasting. Note carefully the temperatures that NIST says the steel THEY tested reached.
There wasn't any substantial weakening of the steel caused by the fires. The fires were weak and greatly spread out. Remember, each floor was roughly an acre in size and each floor was covered by 4 inches of concrete.
We can assume that the floors were pretty close to level so this fuel would have been spread out quite thin. In addition, I believe a great deal headed down the vertical shafts that were within the core area.
Just consider the thermal mass contained just within the concrete floors and their ability to hold heat.
And what of the south tower, which went down first. What would have brought it down faster than the north tower?
While you chew on that to formulate a response, let's have a look at the damage the planes were supposed to have made.
So, for example, a steel column with a factor of safety of 1.75 must support 1.75 times the anticipated design load before it begins to incur damage. While this value is typical of steel beams in general, the actual reserve strength of the steel columns in the WTC was higher. When NIST crunched the numbers for the 47 core columns of WTC-1 (in the impact zone, between the 93rd and 98th floors) it calculated that the factor of safety ranged from 1.6 to 2.8, the mean value being 2.1.[65]
This means that the average core column in the impact zone of WTC-1 could support more than twice its design load before reaching the yield strength, i.e., the point where damage may begin to occur.
Note "begin to occur", Parados, not lead to catastrophic failure. Read on. .
It is important to realize that the factor of safety is not a threshold for collapse, but a value beyond which permanent damage may begin to occur. As the NIST report admits, even “after reaching the yield strength, structural steel components continue to possess considerable reserve capacity.”[66] This is why steel beams and columns typically do not fail in sudden fashion. The loss of strength is gradual. No doubt, this helps to explain why, although fires have ravaged many steel frame buildings over history, none had ever collapsed–––until 9/11–––nor has any since.
What all of this means, of course, is that even in the most improbable worst case, in which many or all WTC core columns lost half of their strength, there was still sufficient reserve capacity to support the building.
According to the NIST report, the outer wall’s factor of safety against wind shear on 9/11 was extraordinary, i.e., in the 10-11 range.[67] Why so high? The answer is simple: On the day of the attack there was essentially no wind, only a slight breeze.[68] For this same reason nearly all of the perimeter wall’s design capacity was available to help support the gravity load.
As the NIST report states, “On September 11, 2001 the wind loads were minimal, thus providing significantly more reserve for the exterior walls.”[69] When NIST crunched the numbers for a representative perimeter column in WTC-1 (column 151, between the 93rd and 98th floors), they arrived at a factor of safety of 5.7.[70] Assuming this average figure is a typical value we arrive at a reasonable estimate of the perimeter wall’s amazing reserve capacity.
Even if we subtract those columns severed/damaged by the impact of Flight 175, and the lost capacity due to the alleged (but unproven) buckling along the eastern perimeter wall,
there was still a wide margin of safety, more than enough by several times over to support the outer wall’s share of the gravity load, with plenty to spare.[71]
The WTC’s tremendous reserve capacity was no secret. In 1964, four years before the start of construction, an article about the planned WTC appeared in the Engineering News-Record.
The article declared that “live loads on these [perimeter] columns can be increased more than 2,000 percent before failure occurs.”[72]
A careful reading of the piece also gives insight into why the plane impacts were not fatal to the integrity of the outer wall.
The reason is simple: the perimeter columns were designed to function together as an enormous truss, specifically, a Vierendeel truss. The wall was inherently stable. After the plane impacts it behaved like an arch, simply transferring the load to the surrounding columns. As the 1964 article states,
“the WTC towers will have an inherent capacity to resist unforeseen calamities. This capacity stems from its Vierendeel wall system and is enhanced through the use of high-strength steels.”[73]
In short, NIST’s own data fails to support its conclusions about the cause of the WTC collapse. The official theory requires the fatal weakening of both sets of columns, and NIST came up short on both counts due to insufficient evidence. Indeed, I would call it woefully insufficient.
