Food for thought.
vaf3 said:
...if anyone else would like to have some sort of constructive discussion concerning any of the topics I'd be glad to participate.
Perhaps I can shed some light...
vaf3 said:
...the steel was heat treated to withstand temperatures of 3000 degrees for several hours before becoming red hot to the point that it would buckle. The president of the company that supplied the steel stated so in a letter to the head of the national institute of standards and was then immediately fired.
Steel doesn't need to become 'red hot' before being structurally useless. At approximately 550 degrees Celsius (1022 degrees Fahrenheit), steel loses half its structural strength. This temperature is not at all regarded as 'hot'. In any event, a structural steel frame exposed to this magnitude of temperature for only a short duration will be on the verge of collapse if it hasn't collapsed already. In addition, if the steel was as 'fire resistant' as appears to have been claimed, why cover it with fire retardant foam? What would've been the point?
sjdgpt said:
Have you ever built a bookcase or other structure? If all you have in place is the uprights and the top and bottom shelves the entire bookcase is rather weak and prone to flex and stress. But install the back and several shelves and the bookcase can suddenly hold many pounds in a stable position.
Yes, but it's no more stable in an out of plane direction.
sjdgpt said:
Take a look at the towers...It really is the floors of the towers that were critical in holding the upright frames in place, AND kept the uprights from flexing. Suddenly several floors are missing. Missing floors and missing exterior skin means greater stress on the floors above and below the points of impact.
Not quite. There's nothing wrong with flexure. All structures flex to some extent. Flexure (or any force for that matter) is only a problem when its magnitude exceeds the strength of the member subjected to it. Missing floors will however mean that the columns effective length (length between points of effective lateral restraint (i.e. floors) will have increased and will therefore be far more liable to buckle (elastic critical buckling is a function of effective length squared).
sjdgpt said:
This flexing could have caused the towers to topple to one side or another.
All structures are (or at least should be) designed against disproportionate collapse. In other words, the failure of, say, one column, shouldn't cause an entire structure to collapse. A structural Engineer will design a structure to be 'indeterminate', meaning that parts of it can fail, but a safe path to take loads down to the ground will still exist. Example: Take a leg of a three-legged stool away and the structure will collapse. This is a 'determinate' structure. Take a leg of an 'indeterminate' four-legged stool away though, and it'll still be fine.
sjdgpt said:
As the fires burned, those small bolts and welds would become critically stressed very quickly. All it would have taken would have been one critical bolt to have given way, and an entire floor would have started to fall.
It doesn't necessarily follow that because something is small, it'll be the first thing to fail. As for it only taking 'one critical bolt...', well, actually, all it would've taken was 'one critical
anything'.
sjdgpt said:
The first floor to fall would have been a slow reaction. But the impact and weight of that floor (and the residual debris) would have been far too great for the second floor. (and even greater for the 3rd, and then fourth etc floors)...
Yes, this bit's true. It should however also be noted that it's not simply that the second floor from the top couldn't carry the first etc, but that due to the
nature of loading, i.e. dynamic (in other words 'sudden'), the second floor would 'feel' far more than simply the weight of the first at impact.
jonnythan said:
There's no such thing as steel that can maintain 100% of its shear and torsional strength at that temperature.
Torsion is just another form of shear.
jonnythan said:
When you take 5 minutes and realize that a commercial airliner is a tin can made to be as thin and lightweight as possible while being just strong enough not to break itself, and that this tin can crashed directly into a wall made of reinforced concrete and glass, it's easy to disprove this crap.
Except that you neglected to account for the fact that your 'tin can' has a massive amount of energy associated with its speed.
vaf3 said:
Even if it did fall straight down, those top thirty some floors would not have been enough to bring the rest of the building down. That building was over engineered to withstand almost anything.
Unfortunately this is not true. Whilst the factors of safety on tall buildings are doubtless greater than for 'lesser' structures and the buildings in question
were designed against collision from an aeroplane, nevertheless they were never designed against that
size of aeroplane (which did not exist at the time the buildings were designed) travelling at that
speed (refer to above comment regarding energy) and flown
deliberately into them.
vaf3 said:
...the top would fall and maybe damage some of the building but it would not have brought the entire thing down.
As with most things that must consider safety, a balance has to be struck in design between strength and economy. Sure, you could design a building strong enough to withstand the weight of a floor crashing on top of it, but the structural members would be so massive that they'd cost a ridiculous amount of money. In any event, no building would ever be designed so that a single floor/columns etc. could carry the magnitude of loading imposed upon it by the upper portion of the towers being discussed here.
Alandamp said:
Now your comment about there not being enough mass above the explosion to cause a symmetrical collapse.
How much (or how little) mass was above the explosion is irrelevant as to whether or not a 'symmetrical' collapse would occur.
vaf3 said:
...I just can't see how that building would come down like that without aid.
It would take an extreme event to bring down a tall building. Unfortunately, that is, as we are all aware, exactly what occurred.
vaf3 said:
Those of you who are professionals say so. I have several professors that have phds in several fields that have argued against your points. I may not be an expert but I will take their word for it.
Well, I don't know about the professional bit,
but I really wouldn't just take folk with a Ph.Ds word for it.
vaf3 said:
Ill give you your ton, now show me the other million that should have been inspected.
The chance of the structural steel being under strength is miniscule.
jonnythan said:
Having a PhD, even in an engineering field, doesn't mean you know the slightest thing about building construction or metal fatigue. Even a mechanical engineer can easily go through college, get a Master's, and get a PhD without ever learning anything more than introductory college textbook steel properties, but to most people that PhD means he's an automatic authority.
Agreed (though fatigue, at least in the structural sense of the word, would've had nothing to do with the collapse of the towers). A PhD looks in great detail at a
tiny facet of a subject.
vaf3 said:
The people i referenced that I spoke with, the ones with teh PhDs, the one was in physics, and the other was in civil engineering.
civil Engineer? Bah! What do they know? (sorry, Structural Engineers always think they're better than civil
)
jonnythan said:
I...don't plan on learning anything that will allow you to analyze the metal fatigue obtained by burning typical building contents mixed with jet fuel for an hour+.
Fatigue failure is caused by repeated cyclic loading of a member. Given enough cycles, the member will fail by fracturing in a sudden and brittle manner. Fatigue is a
long term phenomenon.
Sleestack said:
The PhD in civil engineering could or could not have real world knowledge, but I am leaning quite heavily on the latter.
Agreed.
Sleestack said:
...you're not an engineer yet. You're an engineering student.
vaf3 said:
I am well aware I am still a student thank you for the painful reminder.
Do not apologise for being a student. There is
nothing wrong in being one.
warhummer said:
...in all fairness I did not view this video and cannot refute everything (or anything for that matter) that they say. But I think its origins follow along the same lines as the crackpots who refuse to believe we put a man on the moon...
Oh come now Warhummer. That's just going too far.
