Whatever, you are the "man"... Good luck finding someone to "debate" with you on this dying boring, re-hashing, paranoid about 9/11 thread... V77.... over and out.
Sorry, this reply is long. I thought it necessary to quote two levels of discussion, since otherwise it would be too hard to follow what's being discussed. Also had to break it into multiple posts to avoid 10,000 character restriction. Remember that what I said here was in response to man's suggestion that if point heating of the steel beams were a significant factor in initiating the collapse of the towers, then we would surely expect that more steel frame buildings would have suffered total collapse due to fire in the past. My major point here is that the design of the buildings is in many respects unique and that they are not easily comparable to other steel frame buildings. This is not an assumption on my part. This is simple fact. So to reason, as man did, that other steel frame buildings having very different construction should have behaved the same way as the towers did in earlier fires that were caused by quite different mechanisms is simply a logical error. Your own statement that the buildings `were very tough' is purely qualitative, of course. To my knowledge: the towers were designed to survive a direct hit by a major hurricane, and some level of earthquake, that's correct. But also, to my knowledge, there is no evidence that `multiple' Boeing 707 crashes were ever even considered during the design, and it sounds unlikely to me on the face of it. Surely no one would have imagined it very likely that multiple boeing 707s would ever crash into one tower. How many would `multiple' be, in any event? Would it be as many as 3 or 4, perhaps? There is reference made in documents that were kept on record with the Port Authority of New York to an `impact study' that was done of the crash of a single Boeing 707 into the towers. There's no specific documentation of the details of this study that has come to light. The conclusion was that only local structural damage to the towers, insufficient to cause their total collapse, would have resulted from the impact. This conclusion seems to have been borne out by the events on 9/11, since had the deflection of the buildings from vertical caused by the impact of either Boeing 767-200 (ER) been sufficient to damage either tower on floors very far away from the impact zone, then we should have expected both to see some serious immediate damage at distant points on the towers and probably also to see a collapse following the impact far more quickly than what occurred. It is certainly not clear that the combined effects of fire and local damage were looked into in this study, and it's not clear either what impact velocities were considered for the 707. So I think your assertion that `they were strong enough to withstand multiple boeing 707 crashes' is an assertion without basis in fact.
What are you suggesting? That the entire weight of the building could still have been borne by the core if the perimeter tube were suddenly completely absent? The core was designed to easily support the static weight of the building as long as the core columns were true and the horizontal forces on the columns remained balanced. In this case, a large fraction of the weight of the building was directed vertically down the core, compressing the core columns vertically. A significant fraction of the weight was also carried by the perimeter tube. Potential horizontal buckling of the core columns was actually a design concern. There was worry that the elevators, on passing rapidly up and down through the central core, might cause sufficient buckling of the interior columns to compromise the structural integrity. The elevator shafts were specially designed to deal with this worry. Here's a hypothetical collapse scenario, if the perimeter frame tube were suddenly totally removed. [0] The outer edges of all of the floors would move downwards under gravity, since there would be no remaining external attachment points for the floor support trusses. The downward fall of the floors would lead to enormous and unbalanced downward and outward pointing forces at all of the attachment points of the floor support trusses to the central core. [1] This would produce huge dynamic bending moments on the core columns, which would not remain true for long. Core columns, when sufficiently pulled out of line near the attachment points, assuming these didn't fail first, would fail, and the core would be gradually torn to pieces. The floors would fall off from the core, and while some of the core might remain standing at the end of the process, it would be severely weakened. Yet, firemen did not manage to extinguish the fires with just a couple of lines. I beg to differ with your assertion that there is no reason to believe the temperatures were high and the fire was strong. Some engineers studying the collapse have actually published papers arguing that the fires were hot, strong, and widespread enough to have eventually caused the collapse all on their own, even without the major structural damage that it is suggested the impacts caused. While the jet fuel was burning, certainly, high fire temperatures could be reached. Fires are evident externally on more than one floor in each tower. That is widespread by definition. We can't see all the way into the core, of course. But that is not grounds to suggest that there weren't strong, sustained and widespread fires there. It would certainly be expected that there would be. There was considerable combustible material on the planes and in the towers. The large amount of empty space in the building design would have allowed all of the debris to be swept directly in towards the core. Adequate is not the right word. I should have said intact rather than adequate. The insulation was theoretically adequate to protect major supporting columns for up to 3 hours in a fire naturally, assuming that it was intact and no metal was exposed directly to fire. These survival times were specified in the fire codes applicable at the time of design in 1962, which originated in 1938. In 1968, the requirements of the code were weakened by as much as an hour for certain interior structures, and the actual construction was according to the new code. (See executive summary of NIST report). There's good reason to believe that the crashes of the airliners could have stripped the insulation from various structural support members, exposing areas of bare steel to possibly high fire temperatures. The insulation on some structural members had been reduced from 2 inches to 1/2 inch during construction, it appears.
What?! Sorry, but I have to wonder whether you have ever actually looked at the NIST report. What you say here is plainly wrong. I suggest taking a look at the report right now. Turn to page 175 (it's 229 in the pdf file) of NIST-NCSTAR1 (Draft). The pdf is available here: http://wtc.nist.gov/pubs/NISTNCSTAR1Draft.pdf Section 8.3 is titled Findings on the Mechanisms of Building Collapse. I'll quote a bit to make it easy: So the NIST theory is certainly that the crashes caused damage to the towers, as well as fires. It's the combination of these that eventually caused the collapses. Disbelieve the theory if you want, but the NIST clearly said that this is how the collapses were initiated, and that the crashes were partly responsible.
Steel conducts heat, it's true, but if you keep on heating it at a given point for long enough you will set up a temperature gradient in the steel, with highest temperature at the point of heating. It's a question of conduction of heat versus rate of heating. Melted steel was not definitely found, I think. I have seen pictures of stuff at ground zero that maybe looks to me possibly like melted steel, pictures taken on days later than 9/11, but what is the evidence that this is actually melted structural steel and that it was melted on the first day? I'm not aware of anything solid to prove this. That evaporated steel was found in any significant amount is practically impossible to believe. The boiling point of iron is 2861 °C. I think it would take very special explosives or possibly electrical arcs to produce temperatures anything like that high. What's the actual evidence for the claim about the evaporated steel?
So you agree that this collapse mechanism is a possibility. I agree that explosives would be a possible way of cutting the supports on one floor. I disagree that it would be very easy to do without getting caught, and I have problems understanding how one could know what floor to do the demolition work on in advance. After all the buildings collapse starting at those floors where they were hit by the aircraft. So one would either have to wire up many floors for demolition, or else tell the pilots almost exactly what floor to steer towards. And then, take a careful look at the paths that the airliners flew on before they hit the towers. One of them practically missed the South tower, it hit travelling on a wild curve, at one corner, and in a steep bank. Well, OK. You might think that it's harder than I say. But anyway you agree above that this is a possibility. I'm simply telling you that I actually have done this calculation for myself, and I'm also saying that it was not that hard for me to estimate what the dynamic stress would be in the best possible case for the chance of building survival (perfectly symmetric and uniform fall of the upper stories onto the lower stories). The only really difficult part was to know how stiff the structural steel is, and how much energy bending it might absorb, and to figure out how to model how the building's floors would respond when the upper part fell downwards and impacted on the bottom: what it's elastic properties are and so on. Structural engineers know that sort of thing really well, physicists don't I'm a reasonably good physicist, and I was able to think of a simple model (actually more than one) in which I could estimate the numbers by hand. It would be hard if one didn't know any physics. I would be happy to provide more detail on what I did if you don't believe this, but it turns out that some structural engineers who looked at the question came up with basically the same ideas as I did. The idea was actually published only very shortly after 9/11.
Multiple jet airliners: I don't think these were ever considered. Hurricanes, definitely yes. The Madrid building did actually partly collapse, but it's true there was no total collapse, there. But the Madrid building is a much more standard design ... there are many more structural columns per unit area of space on the floors, and there is also much less open space on the floors. In addition, there was no airliner crash in Madrid, so the insulation on the beams may well have been in much better condition. That's not true, as you can see in the NIST report itself, referenced and quoted above. I don't see things the way you do. While I definitely agree with you that a relatively small number of cutter charges could have done the job, due to the inherent dynamical instability of the towers, I think that it's very hard to understand how this could be carried off in reality, without leaving a single trace, and without being discovered. Thanks very much for the links you provided, I will read more of them when I get more time. Cheers and good trading to you! Thanks also the effort put into your response. I'll respond to man later on.
NIST Reports, What expert findings?, Theories of collapse? All the metal debris of WTC1 and WTC2 and WTC7 was gathered, loaded onto cargo containers, and shipped to another country (possible China) for scrap. I guess without the ability to analyze the metals structural integrity, we will never know what caused the buildings to collapse. How can one write a theory, or conclude a finding, or make any opinion at all about those buildings. The evidence is gone. WD