Let's address Tony's point's one by one:
I just want to explain why it is extremely difficult for a steel framed high-rise building to collapse due to fire.
First, the columns will not get very hot as they have a heat transfer path to cooler areas.
We have a good idea of the column temperatures from actual modeling, not from your bare assertions. This bare assertion adds nothing to the discussion. There is no significant disagreement over the column temperatures in any of the models.
Second, steel frames are built with factors of safety and it is difficult to heat large structural members to the point where there is no safety margin left with the limited fuel in an office fire in any given space.
Difficult != impossible. Pre-9/11, steel framed buildings were built with purely prescriptive fire abatement systems (insulation, sprinklers, etc.) based on the size of the individual building elements. After 9/11, in response to the NIST reports,
the ICC adopted (see also
here specifically re disproportionate collapse changes) and many localities (
including NYC) also adopted amended codes so that buildings needed to (among many other things) also take the design of the building into account by factoring in the prevention of potential disproportionate collapse scenarios as well. This change was in direct response to the people who are most expert in the world on the subjects of fire science and the engineering of tall buildings to reviewing the NIST reports and related materials and recognizing there existed real potential vulnerabilities in these building under certain circumstances. (None of the people who actually do real work in this area as actual experts are members of AE911Truth, by the way.)
A building may have a fire for a significant time with the fire traveling through it but that heat can only be applied in any given local area for a relatively short time, as the fires run out of fuel in local areas and burn out in an hour or so in a given area.
How long exactly, Tony? The last time you brought up the fire models, you advocated an indefensibly short period based on a patently flawed paper from Robert Korol (
which model erroneously omits preheating and truncates the direct heating period without any basis). You have never actually defended that clearly flawed analysis or otherwise explained exactly how long the heating should be. As you know, NIST,
which did not attempt to model the most extreme fire scenarios possible, found significant local heating over periods in excess of 4 hours in many places. You are not making an actual specific claim here; you are merely trying to poison the well.
Since the columns must fail to have a collapse, the only way to have that happen is for the horizontal members to somehow dislodge and remove their lateral support over a significant number of stories for the columns. This is what NIST, ARUP, and Weidlinger all tried to show happened.
Correction: this is what NIST, Arup and WAI demonstrated could happen in a variety of ways in a variety of reasonable scenarios that are consistent with the conditions of the building observed that day.
NIST failed to do so, as [we feel] their model ignores and omits items that would prevent this dislodgement such as column side plates, girder web stiffeners, and lateral support beams. In addition, their model prevents deflection of the exterior due to thermal expansion of the horizontal members causing all of that deflection to move in one direction towards the column they say collapsed. For some here to say their model was high fidelity is a travesty when it is realized they ignored or left out pertinent structural features to try and accomplish the horizontal dislodgement. In reality, with those features included the NIST WTC 7 report claim is impossible.
The specific points you bring up re potential inaccuracies in NIST's model that may have added error to its calculations are all fair points and can be subject to further debate an analysis. But the degree to which correcting for them would have altered the outcome in NIST's analysis is dependent upon many other factors as well, including--first and foremost--their actual heating model, which was extremely detailed and included a variable progression across the entire building, from which NIST modeled fire damage on 16 floors simultaneously. The damage NIST modeled was
path dependent. Yes, elements near to each other all reached relatively similar temperatures at some point as a general matter, but in NIST"s model, they reached their temperatures individually in a certain predetermined sequence over the course of six hours. Hulsey did not apply such a heat model. As far as we can tell, all he did was take the a snapshot of the NIST temperatures at 6:00 pm and apply them to each element as if they were the maximum temperatures such elements reached. But that's not accurate. Many elements had already been heated more extensively and started cooling at that point, while many other elements would still yet be heated more prior to the collapse. Moreover, Hulsey only modeled two floors and, on those two floors, the portions of the floors he modeled fire damage were smaller than portions of the 16 floors on which NIST modeled fire damage. These limitations (along with other modeling and software differences) of Hulsey's model make it impossible for him to claim his structural revisions were implemented in a controlled way such that we can conclude that those structural changes, and not the limitations, were the cause of the discrepancy in outcomes as between Hulsey's model and NIST's.
Moreover, it is worth noting again that, in any event, NIST's model only showed one way (the way NIST through most probable) that fire could have caused the collapse of the building. Even if NIST was mistaken about that, it does not mean that collapse mode didn't occur under fire conditions different than what NIST modeled, or that any other collapse mode could not have occurred. This is pure, basic, obvious logic that should not even to be stated, but somehow it is completely lost as you, AE911Truth and Hulsey insist on being dishonest about the scope of his findings.
ARUP had a fatal error in trying to show the falling girder would break through the next floor down. They used an infinite stiffness for the falling girder and claimed an enormous and fictional impact load. When the correct stiffness is applied they fall far short of the load required to break through the next floor down.
Tony, I already corrected you three times on this in this very thread.
Arup did not do floor collapse propagation calculations. Arup found multiple ways in which the girder could become unseated in heating and cooling scenarios (which were confirmed by WAI). These ways were completely independent of NIST's findings and demonstrate that the girders around column 79 could have failed. Nordenson, who retained Arup to do the girder failure models, then did hand calculations about floor collapse propagation, which hand calculations were explicitly conservative and assumed the floor beneath the collapsing floor was in pristine condition. Of course, Nordenson also made an error re the stiffness of the falling floor, which error we've discussed ad nauseum and which WAI acknowledged and corrected for (more on that below). That error does not have any bearing on Arup's failure calculations, NIST's failure or collapse propagation models, or WAI's failure or collapse propagation models. Moreover, that error does not have any bearing on any scenario not modeled by Nordenson, including scenarios in which the lower floor is not conservatively (and unrealistically, in the case of WTC7) assumed to be pristine amid raging fires for hours.
Wedilinger acknowledges that ARUP can't break through the next floor down and then goes on to say that in another location the fires superheated the steel on two contiguous floors with the top one failing and falling on the lower and finally getting enough momentum to continue propagation with two floors falling. Of course, they have not publicly released the thermal analysis they claim shows these extreme steel temperatures.
WAI corrected for Nordenson's error and found that, if recalculated correcting for stiffness
while still accepting Nordenson's conservative assumptions re the condition of the lower floor, then the collapse would not propagate. That was it. That was the end of their direct analysis of Nordenson's hand calculations. But, as you know, WAI also ran a full collapse model and found, via such model, that in the scenario they tested, floor collapses would propagate from the girder failure they identified as initially failing. This model does not rule out any other model, except to the extent WAI's assumed conditions were actually more correct than the assumed conditions of the other models. And, again, your claims re extreme steel temperatures in WAI's study are purely speculative and an attempt to dismissive out of hand something you can't otherwise argue against. And it is worth noting that WAI's report does not conclude that similar failures wouldn't have occurred at lower temperatures; it just details the collapse scenario they thought most likely given the fire scenario they thought most likely. Plus, I have demonstrated to you elsewhere that WAI's temperatures were consistent with the temperatures reached in the Cardington studies on steel failures in fire (the
same post as cited above includes the Cardington beam steel temp graphs).
In his presentation Dr. Hulsey mentions that if the columns can't be compromised by heat directly then it can only be horizontal dislodgement which could cause a failure of the columns. It seems that he looked for horizontal dislodgement by analyzing the floor frame and slabs in composite, partially composite, and non-composite situations and could find no instance where the horizontal members would adversely affect the columns to the point of collapse. That would be why he felt he could make the statement that fire could not have caused the collapse of the building.
Hulsey did not look very hard for girder dislodgement. In fact, he ignored every scenario tested in which girder dislodgement was found to have been possible, except for one, and he did not even model that one scenario under a very rigorous temperature model. Moreover, he did not attempt to model any scenarios that have not yet been modeled to date. His conclusion that the building could not have collapsed from fire is does not at all follow from the work he has done to date. Even if he had done his one model perfectly, his conclusion would still be unsupported. There is no way around this. Why can't you just admit that?