Both buildings had the same exact design from top to bottom. A central core of steel support columns surrounded a central service area (containing elevator shafts, utilities, stairways, etc.). Every floor of the building had steel trusses on (approximately 3 ft centers) that spanned the entire distance from the center column to a matching column on the exterior wall. There were no intermediate columns. Each vertical column was load bearing for every floor above. The floor trusses bore only the weight of that floor's concrete, but they also supplied the rigidity that held the exterior columns in place. When several contiguous floor trusses sagged, that caused the outer wall to pull inward, causing the upper loads to begin moving downward.
If you watch the collapse videos carefully, you'll see that the first tower didn't fall straight down. There was a definite cant to the upper segment as began to fall. This suggests that the first truss failures were somewhat localized for the first few fractions of a second. But once the weight of all the upper stories began to fall on the lower floors over that section, the stresses generated on surrounding members would instantly become enormous, and they would start to fail, too. The pancake behavior appears to have straightened out a little bit, from what I can tell, although it's hard to really tell after the smoke and pulverized dust obscure the buildings.
You talk about the heat from jet fuel being insufficient. Why do you keep insisting on this point? The plane crash simulation done by Purdue Univ. shows the primary impact damage occurring on two floors of each building, but let's really go wild and say that perhaps three or four floors may have caught fire. Once the fire had started, the jet fuel probably burned off before the building fell. But as you've been told before, the building itself provided the combustable materials that sustained the fire. Synthetic fabrics in carpeting and drapes burn very hot. And too, you're ignoring the fact that even if a certain fuel doesn't burn at a high enough temperature to weaken the steel trusses, the heat from the fire is building up and collecting at the ceiling levels over time. The heat trapped above the fire during the 56 min. the building stood would be astounding.
FYI, when construction began on WTC 1 and 2, asbestos was used as the primary insulator on the steel members. About midway through construction in the mid 60s, the politically incorrect asbestos was discarded as an insulator, and other safer (at least for the construction workers) but less effective insulation material was used for the top half (roughly) of both towers. Also, most analyses presume that much of the insulating material was blown off on the steel nearest to the plane crash due to the impact, anyway. So using asbestos might not have made any difference, anyway.
The internal service core of the towers was not very strong. Three layers of drywall only provided the fire proofing that separated the office areas from the service core. When the planes crashed into the building, the drywall wasn't strong enough to withstand the impact, and the stairways and elevator shafts immediately became chimney stacks. All the people on floors above the plane crash were trapped, and could not get down the stairwells.
As for steel beams being a heat sink, that's just being silly. Any material can be a heat sink. But steel is a excellent conductor of heat. If there was enough heat at the ceiling level, and no insulating material to keep heat away, the steel trusses above the fire were going to get very hot, very fast. And that heat will not be transported away from the steel, because there is very little surface area connecting each member to the others, just a few bolts (or rivits) and angle clips at each junction. Once the trusses heated up, they would have no way to disperse the heat away.
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Weichert Wayne PA Patrick J Nolan 1-610-687-4400 Info@TheRealEstatePal.com
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