Since I have to assume you are suggesting my above reference was showing disrespect for Mr. Scheuerman, let me quote the man as a means of explaining the lack of warmth in which I regard him;
I am not interested in your reasons for disrespectful conduct. I only ask that you keep this respectful, as I ask of everyone posting in this thread. I am striving for a factual discussion, not an analysis of character. I have put aside my own differences for this discussion, and you should try to do the same.
Am I confused---or are you displaying some of that disrespect you periodically feel compelled to remind others about?
You are confused, and I say that with no trace of disrespect. If you do not come from a technical background, there is no reason at all why you should have the correct intuition about the off-nominal behavior of large buildings. Even many experts, structural engineers and the like, had never thought about the fine mechanics of building collapse, and some were surprised. However, now that we've had a specific example to think about, we can come to some conclusions, many of which were obvious from the beginning had we asked the right question.
Must I remind you that prior to 9/11 there were no comparable fire induced building co
llapses to base your; "This simply is not expected under almost any conditions", statement on?
The issue of building analogues and precedent is not important to this discussion. You will note that I did not cite precedent in my previous response, instead discussing the theory and mechanisms that apply to WTC 7. The basic equations of structural engineering, strength of materials, and solid mechanics are well understood and apply fully to the situation at hand. This is sufficient to explain the collapse behavior, whether or not we have a comparable example from history.
Another reason why precedent is meaningless here is because there isn't one. There are no examples of analogous situations that didn't result in collapse, that collapsed slowly, or that toppled over either. WTC 7's situation is most unusual.
Much like the NIST 10,000 page WTC Twin Tower Collapse Report, I continue to find your responses to be similarly voluminous, especially in their repetition of textbook knowledge yet still failing to address my points.
I'm afraid I don't know how to respond to this. You asked why WTC 7's collapse features, i.e. a relatively level collapse of the entire perimeter, was consistent with fire and did not require explosives. That is precisely what I provided you in my previous post. If you have a more specific question, please feel free to ask.
Up until 9/11 we expected the fire-induced collapse of such structures to be an impossibility!
This is not true. The firefighting community has always regarded collapse as a serious concern in skyscraper fires, and this is why firefighters were all pulled away from WTC 7 hours before it actually came down.
Additionally, there are several cases of skyscraper fires predating September 11th where collapse was thought possible. One Meridian Plaza in Philadelphia is perhaps the closest analogue. While this building did not collapse, it was expected that it might experience a total collapse, and thus firefighters were pulled from the structure. Unlike WTC 7, this was a structure that was unoccupied and thus had a much lower fuel load; it did not have additional ventilation caused by debris impacts; it was a more traditional post-and-beam design, lacking the long-span floor members found in WTC 7; and it was fought by fire brigades unimpeded by destruction of water sources and so on. None of these differences are relevant to the point I want to emphasize, which is that firefighters did indeed know the danger of total structural collapse in skyscraper fires.
So you're saying that inside WTC 7, the heat was so great, and was sustained over a sufficiently long period of time, that a major column buckled, and that the re-distributed load it formerly supported, was so immense, that all the other major supporting columns failed within seconds resulting in a high speed, symmetrical, total building collapse?
That is basically correct. Because of the exterior appearance of the collapse, we know that most if not all remaining major support columns all failed within a short period of time, but this is not terribly surprising. Load redistribution from one column to another takes mere milliseconds. With each column failure, that load becomes more eccentric and more poorly braced, and cascading failure is the expected result.
You are saying that the WTC 7 structural engineers must have been aware that a single column failure in this lower location, if it should occur, would lead to a catastrophic total collapse of the whole building, and yet they didn't sufficiently over engineer this vulnerability to reasonably withstand the danger you perceive---office furniture fires?
Now that does stretch the imagination, especially given that NIST has now ruled out the on site diesel fuel as a factor. Obviously you appear to have no problem embracing the notion of such an engineering gamble.
Actually, that doesn't stretch my imagination at all. Redundancy is not the usual approach to this problem in the first place, and there are many structures that are susceptible to single-point failure. Furthermore, there is hardly any treatment of system redundancy in the building codes. Building codes tend to focus on performance of
individual elements, not the structure as a whole, and this is particularly true of older building codes. Rather than guarantee alternate load paths, engineers instead calculate the maximum expected load on a given element, apply safety factors as needed, and build accordingly.
Another point to keep in mind is that
WTC 7 met its design requirements. It does indeed appear to me that a single-point failure resulted in a total collapse, but that wasn't in the specs. Instead, WTC 7 was designed to provide two to three hours of fire resistance, assuming a large but ordinary office fire. Instead, WTC 7 withstood over seven hours of an extraordinarily large fire, with additional damage and ventilation, without active suppression, before collapsing. It outperformed its requirements by a considerable margin. Therefore, I don't perceive that the designers took a gamble at all.
Additionally, even had the single-point failure mode been eliminated, we don't know for sure that WTC 7 wouldn't have collapsed due to a compound failure only ten minutes later. Few buildings will remain standing indefinitely.
These are the kinds of things that NIST is trying to answer. We know why WTC 7 collapsed, in broad strokes, but we want to know the
details. As I remarked above, this event has no precedent. Destructive evaluations of this kind are extremely rare opportunities to learn. Furthermore, NIST has already recommended modifications to building code that
do consider redundancy and global response, but to do this effectively NIST needs to know where to concentrate our efforts.
You respond with many words but when they are carefully examined, there is an absence of supporting argument and a surplus of speculation. They also read like someone re-writing material that they themselves don't completely understand.
I don't know how to respond to this, either. You are welcome to ask follow-up questions if you find my reasoning or support to be unclear.
"Unspecified floors had several hours of continuous fire."
That sounds impressive but it leaves out the important specifics. What floors? Which hours? How much of the floors were effected and when?
The best information that I have in this respect is the
FEMA Report. FEMA remarks that fires were seen on Floor 11, for one, for roughly the entire duration of the fire, and spread to Floor 12 and 13. (That's "fires were seen," not just smoke.) I pick these floors specifically because this is a strong candidate for the location of the initiating failure. The FEMA Report is quite terse, as you know, and so I am waiting for a more definitive timeline from NIST before attempting to add too much detail to this hypothesis.
"Some will be due to the more oxygen-starved nature of WTC 7."
That statement suggest fires that were restricted in their intensity.
That is correct. Compare WTC 1 vs. WTC 2, for instance -- the lesser exterior damage meant that WTC 1's fire was oxygen-limited, whereas WTC 2's fire was not. I expect WTC 7 to have been more oxygen-limited, and this contributes to a longer duration fire. Exactly how limited, however, I am not in a position to evaluate.
"There also could have been a much higher fuel load in WTC 7."
Why? There could have been any number of things in WTC 7 but we have nothing to base a higher fuel load speculation on. In the case of the Twin Towers, there is at least the argument that the wide profile and horizontal nature of the high speed aircraft impacts could have compacted more of the floor's contents. In WTC 7 the impacts were primarily a vertically gouging falling debris type with a much narrower profile.
No, there are many reasons to speculate a higher fuel load. Dr. Quintiere, for instance, conducted his own survey of office materials and found that the NIST estimates for WTC 1 and 2 were possibly underestimated by as much as a factor of three. I don't know which of them is correct, and I also don't know if there were other factors in WTC 7 -- such as much greater paper file storage in the SEC, floors 11-13, for instance -- but these are questions that can be answered. It's certainly worth considering.
"...direct visual evidence confirms that some areas of WTC 7 were exposed to heat for much, much longer periods than 20 minutes."
Which areas and for how long? After all, there are only a few locations where your point has any relevance to a potential core failure.
Again, that's not really true. If the initiating failure is what we think it was, there were many possible places for it to happen. I need more evidence before I pick which floor and which column was the unlucky one, but I trust you can agree that it is reasonable for it to happen
somewhere on one of the several floors affected.
I really fail to see any strong case from you that suggests that fire stayed at a single critical column support location long enough to overcome the 3-hour fire proofing and raise temperatures sufficiently to cause the column to buckle.
There is no requirement for the
fire to stay at any one location for that long. Fire heats the gases inside, and it is the effective gas temperature that we are concerned with, which can travel some distance from the fires themselves. This is particularly important in a multi-floor fire, where small fires on progressive floors can contribute to an overwhelming gas temperature through stack effect.
Also, as I wrote above, I don't think the core columns needed to get that hot. I believe the collapse mechanism of WTC 7 was gradual, with many relatively small displacements -- and relatively cool temperatures -- contributing over several floors. The long period of time between start of fire and collapse is one reason why I believe this, as outlined before.
At approximately 2:00 p.m., firefighters noticed a bulge in the southwest corner of 7 World Trade Center between the 10th and 13th floors.
And it's not possible that this reported bulge on the southwest corner between the 10th & 13th floors was localized debris-related damage?
No, it is not possible. I do not know the precise location of the bulge, but I see no reason to think it was right along the corner's edge. The damage shown in that well-known photograph appears to be quite localized, perhaps extending only one or two bays along the face. The bulge is probably near this damage, but certainly not part of that damage.
Regardless, again, the firefighters saw this bulge appear. It was not there before. It was, therefore, not caused by debris-related damage. It was caused by heat. Heat weakened the structure, this led to large-scale displacements, and that created the bulge. There is absolutely no other explanation.
Again, the existence of the bulge guarantees that heat can cause structural damage, and therefore heat can lead to collapse. This particular bulge, being low in the structure, is further evidence that the initial failure happened low in the structure as well. My previous post explained why, for a tall steel-framed building, a low initiating failure is expected to lead to a global and quasi-symmetric collapse.
