I am a structural engineer specialized in shipbuilding. I have inspected many ships built of steel damaged by fire and overload of various kinds.
I don't care. I care about mathematics, evidence and logical analysis.
None of these ships or their structures has ever collapsed by fire. Deformed, yes. I have some observations regarding the WTC2 collapse that may be of interest:
This point has been shown in error.
The NIST NCSTAR 1-6D report suggests that the WTC2 collapse was due to the following:
"Buckling of East Wall and Collapse Initiation
With continuously increased (sic) bowing and axial loads, the entire width of the east wall buckled inward. The instability started at the center of the wall and rapidly progressed horizontally towards the sides. As a result of the buckling of the east wall, the east wall significantly unloaded, redistributing its load to the softened core through the hat truss and to the south and north walls through the spandrels ( …). The section of the tower above the buckled wall suddenly moved downward, and the building tilted to the east ( …).
The section of the building above the impact zone tilted to the east and south (observed at about 7° to 8° to east and about 3° to 4° to south, …) as column instability progressed from the east wall to the adjacent south and north walls. The release of potential energy due to downward movement of the building mass above the buckled columns exceeded the strain energy that could be absorbed by the structure. Global collapse ensued (sic)."
That's page 321 in case anyone else is following along.
According to other NIST reports the total mass above was supported as follows:
50% - by the 47 core columns.
12.5 % - by the south wall columns (abt 80)
12.5% - by the east wall columns (abt 80)
12.5% - by the north wall columns (abt 80)
12.5% - by the west wall columns (abt 80).
A side note here, the corner columns of the WTC complex held, by themselves, about 1/5th of the load on the core. See NCSTAR 1-1, page 8 for details on the structural subsystems.
About 80% of the wall and core columns were intact after first impact according NIST and the tower structure carried the mass above.
Again, columns that were in tact did not necessarily have the same load capacity as they did before impact. Your analysis seems to hinge on the idea that any in tact column is still capable of carrying 100% of the load. That's a ridiculous assumption.
Then there were fires in the office spaces between the core and the outer walls. The outer wall columns were always cooled by fresh air so they were unaffected by the heat.
Excuse me? Just because a column is cooled by fresh air on one surface does not mean it is impervious to effects by heat. That is a wildly inaccurate statement. Section 3.2.1 shows NIST's analysis of the heat effects in the exterior wall for WTC 1.
We are told that the east wall, that carried 12.5% of the mass above, buckled inward due to axial loads some minutes before the collapse, which BTW are constant and not increasing, as suggested. The buckling deformation is not big as there is still some support from floors inside.
Actually, we're told that the columns on the east wall buckled due to a combination of increased axial load and increased out of plane loading due to floor sagging. These are the infamous "pull in" forces that are discussed, oh, maybe 100 times in 1-6D. Read page 310 for further details. It seems as though you're intentionally misrepresenting NIST's findings.
Second, while the collapse happened suddenly,
We are then told that the east wall significantly unloaded but not how much.
We are told the column loads prior to buckling.
Let's say that 50% of the load on the east wall that originally carried 12.5% of the total mass above, i.e. 6.25% of the total mass above is now redistributed to (i) the core, and to the (ii) south and (iii) north walls through connecting structure.
That's complete nonsense. You've pulled that number out of thin air and assumed that it completely redistributes to areas of the WTC towers which you assume are undamaged by fire. How does that assumption have any basis in reality?
NIST describes, in detail, a load cycling from damaged exterior columns to less damaged exterior columns, and further to the core columns. It is a cycle which catastrophically collapsed when load redistribution failed. 30 minutes into the collapse, creep strain was already buckling core columns where the temperature stresses were high. See pages 313 to 318 for the details.
So 6.25% of the total mass above is redistributed. What happens?
It is redistributed to an area heavily damaged by fire. An area that, by the way, continues to shed thermal load onto the exterior columns via the Hat Truss system. Load can't cycle both ways, and when one system fails, all of them do.
Say that 50% of that or 3.125% of the total mass above is redistributed to the core; it will then carry 53.125% of the total mass above. Thus the load on the core increases 6.25% after the alleged redistribution.
Again, you pulling numbers out of thin air is not convincing.
We are told that the core is 'softened' which is not scientific but maybe it was affected by heat.
Maybe? Maybe it was affected by heat? Did you read any of the NCSTAR? Do you understand anything about fire or the effect of heat on steel?
However, half of the core columns were far away from any fires so they could hardly have been affected.
Excuse me? You're talking about load redistribution, and you assume that the only way a column can be damaged is if it is directly damaged by fire or impact? What about load redistribution? Do increased loads and additional thermal stresses also deform and damage columns?
But as the core columns had resisted the fire so far, a load increase of 6.25% due to redistribution could not make the core collapse!
Wow! An argument from personal incredulity! Not only that, you're assuming that because the core columns were able to carry the increased load directly after the impact, they should have been able to hold the weight indefinitely. That's silly.
25% of the redistributed load or 1.5625% of the total mass went into the south and north walls respectively that now each carries 14.0625% of the total mass above. Thus the load on the south and north walls increased 12.5%. These walls were not affected by fire as they were cooled by fresh air. There were some damage to the south wall, but again it did not collapse at impact, so a load increase of 12.5% will make little difference. No deformation of any kind is seen on the north and south walls after redistribution.
Once again, you making up numbers is not a convincing scientific argument.
Global collapse could therefore not ensue due to such load distributions because there were too much redundancy and safety factors built into the outer wall columns (wind, lateral loads, etc) and also in the core columns. You could maybe expect further deformations of structure finding a new equilibrium and the tower may have tilted a little and stopped in that position but sudden global collapse is impossible due to the alleged load distribution!
Ok, your argument was based on the idea that redundancy could have handled the impact of the aircraft and the increased thermal stress due to fire indefinitely. Yet you provide no mathematics to prove it, and your best effort is to make up numbers, fail to account for thermal stresses, and assume infinite load distribution on a static system.
Actually there is no evidence of any sort for the statement "Global collapse ensued".
I can't tell if this statement is sarcastic or stupid.
It is only wishful thinking by incompetent and/or complacent NIST engineers. They know that no steel skyscraper has ever collapsed due to fire!!
So, hundreds of the world's best civil, structural and materials engineers are wrong. As are their academic, professional and international collaborators, reviewers, and the various professional societies to which they belong. And your belief is that they're incompetent.
So what happened? Controlled demolition, CD, from top down? It seems that WCT 2 47 off core columns were damaged first, as the tower actually falls in its own footprint. The outer wall columns break afterwards like spaghetti by the floors being pulled down by the core columns. It seems that the core columns were broken by CD at every 10th floor, or so. NYFD staff noted these explosions, bang, bang, bang just before collapse ensued.
I would implore you to take a logic class. On your first day, the first words from your teacher's mouth will be, "Universal affirmatives can only be partially converted." The fact that all explosives cause explosions does not imply that all explosions are cause by explosives.
It would have been very easy to recover all the bits of the core columns from the rubble and assemble them on a 400 meter long field to verify (a) in how many parts each column split during collapse and (b) how the surface of the broken areas looked like.
I'm glad that your opinion is that it would be "very easy" to recover the core columns. It's too bad no one cares about your opinions.
CD would probably have cut of the core columns sideways to dislocate them so that they could just drop down pulling other structure with them.
That would have caused a radically different collapse than the one seen. The core of WTC 1 and WTC2 remained standing for several seconds after the exterior of the building had collapsed.
Alternatively complete pieces of core columns were blown away. In either case a forensic examination of the core columns would have explained the collapse.
A forensic examination was completed. It is the subject of a 10,000 page report completed by the most advanced and experienced building fire research lab in the country.
If the collapse was due to release of potential energy overstraining the core pillars, the broken areas would look completely different.
I don't care about your opinion.
But as no complete forensic examinations were done for unknown reasons we must find other means to establish the real cause of the collapse. Easiest is of course a complete re-hearing of the case by a competent law court.
Wow! So, lawyers are better able to judge the technical veracity of the NCSTAR than engineers and scientists in the field. I had no idea that the courts were in the business of establishing scientific truth!
