Truss Failure Theory Inconsistent; Critically Flawed

www.ce.udel.edu...

This is a report about a lecture given by World-renowned structural engineer Charles H. Thornton of the New York-based Thornton-Tomasetti Group. He discussed the collapse of the World Trade Center for an audience of close to 250 faculty, students, alumni, and community members on Tuesday, April 9, 2002 in Mitchell Hall.

Thornton talks about how the outer columns were for wind load, and the core was for vertical load, and the floors just basically kept the building square.

"Thornton attached some numbers to the devastation: Each floor of the two towers was an acre, adding up to 110 vertical acres apiece. Compressed, however, the rubble from the two buildings would fit into a surprisingly modest-sized hole–about 65 feet by 500 feet by 1,000 feet. In the six months since the collapse, some 1.2 million tons of debris have been removed from the site."

I would think that we could have set the building debris aside somewhere for eventual study.

Also, I would argue that the materials WERE sorted through to a large degree, in the search for things other than building materials...

Why ship it off?...That's my biggest question. Can you answer it, BigTrain?

Originally posted by cryingindian
Why ship it off?...That's my biggest question. Can you answer it, BigTrain?

I cant give you the answer as to why they ultimately choose to, because I was not in the decision making process. However, on what I know, im guessing it was all about time and money. Do we have the resources to sort through every single piece of over 15 aircraft carriers of debris weight? Im sure they said, save the most useful members to analyze, and just ship the rest away.

I think if they tried to sort through every piece, they would still be sorting today at a cost that would be in the billions of dollars.

As with all things, id say it was becuase of money.

Train

BigTrain...I missed your point of the Airliner weight adding to what was asked of the floor trusses to support. I agree that would be a great deal of additional weight. Very likely enough to cause initiation of collapse...

I'd still like to know why the concrete turned to a fine dust, and why the building fell as fast as it did.

What could cause the central core to disintigrate all the way down to the ground?

Does anyone know if there's a way to determine the strength mix of the concrete mix used in the core, by chemical analysis of the dust?

I've seen suggestions that in the 70's, 5000 psi compression strength would have been considered high-strength. I recently used 4000 for the footers for my 12'x30'
addition...one story.

Was too much being asked of the concrete in the towers?

But they stood for 30 years. Granted no jets hit them during that time.

Like I've stated before...I'm trying to find a way to believe the "official" story.

Maybe the impact cracks the concrete in the core...crumbling of the core begins...
More damage on one side produces an effect like the one illustrated by Valhalls envelope of the whole building, offsetting the center of gravity, bending the core the entire length and poof...???

Originally posted by BigTrain
They were not designed to hold large standing crowds, floors are not designed based on occupancy, they are based on use, which is based off probabiity. I believe office live load, off the top of my head, is like 50 psf. The point is, these arent super floors.

Depends on which floor, which depends on which building. The office areas of WTC1 did have 50 psf ratings, but I'm not sure of the safety ratings here, which would be important considering we want a failure. The core had 100 psf on a typical (upper) floor, according to NIST anyway, and the mechanical floors (such as the one right under the WTC2 impact location) appear to have had steel beams in the floor slabs along with the trusses themselves, which would be a huge problem for WTC2's collapse by your reasoning.

bsbray, take this scenario, looking from many photos, it would appear that 4-5 floors on the impact side were destroyed by the impact.

No whole floors were destroyed by impact. There were portions of floors, that spanned maybe 4 or 5 floors, that turned out to be relatively small and tapered heavily towards the uppermost and lowermost damaged floors, as shown in the FEMA Report.

That means these floors would have been smashed and debris would have fallen onto the floors not destroyed by the plane impact. Do you not think that all this smashed floor of concrete and steel would not impart a significant load on the existing floors? Remember, all that office equipment, and the plane all had to go somewhere. And you're saying no significant heavy loads. If you still believe me, then where did the debris come to rest after the impact?

Golly gee, why didn't they just all fall right after the impacts, then?

[edit on 4-8-2006 by bsbray11]

Originally posted by cryingindian
Does anyone know if there's a way to determine the strength mix of the concrete mix used in the core, by chemical analysis of the dust?

Maybe this will help?:

Valhall
Something has to have already have happened to the core...

Absolutely..

The only thing that the 'tilt' means in this case, as far as I'm concerned, is that this particular area of the 'perimeter collumn' was compromised enough to allow for this type of 'fulcrum' to occur AFTER the core gave out. (Remember, it looked like the antenna started going down down first before anything started REALLY tilting, no?) after the collapse progressed it's obvious that the 'perimeter tube' 'regained' it's integrity and started 'shoring' things up symytrically. (or trying to) Hopefully you guys get what I'm trying to imply.


It's becoming more and more obvious to me that the core gave out WAY before there were any 'catastrophic' failures in the truss/floor department.


I'd like to comment on this more but got's to get back to work.


More later.




[edit on 4-8-2006 by TxSecret]

I thought the core was steel, not concrete like some have mentioned. Or are we mistaken. I dont remember the core being a tube of concrete.

Train

Originally posted by BigTrain
I thought the core was steel, not concrete like some have mentioned. Or are we mistaken. I dont remember the core being a tube of concrete.

Train

Right, it was steel. It had 2" thick by 16" wide tongue-and-groove gypsum planks that boxed in the columns.

Originally posted by Valhall

Originally posted by BigTrain
I thought the core was steel, not concrete like some have mentioned. Or are we mistaken. I dont remember the core being a tube of concrete.

Train

Right, it was steel. It had 2" thick by 16" wide tongue-and-groove gypsum planks that boxed in the columns.

Ok, I thought so, and the gypsum plates are basically drywall fireproofing.

Train

Yeah, there is at least two (maybe three) accounts of a group of people coming down one stairwell in WTC 2 and coming to a door that was locked. They tried to beat through the sheetrock with a fire extinquisher - no such thing happening. They ended up going back up the stairs and taking another route. 2 inches of sheetrock might as well be a concrete wall when you're trying to bust through it.

I read (on another thread on ATS) an account where a maintenance guy claims he got caught in some area in the core and 'cut his way through the sheetrock with a squeegee'...yeah, and bob's your uncle and the check's in the mail.

[edit on 8-4-2006 by Valhall]

Originally posted by BigTrain
I thought the core was steel, not concrete like some have mentioned.

The above on concrete was in regards to the floor slabs, so maybe that's what you were reading. There have been references by engineers and in scholarly articles, etc., pre- and post-9/11, of the core being "reinforced concrete", but it's commonly accepted by this point, since the FEMA and NIST Reports, that the cores consisted of only 47 box columns, pretty much from top to bottom.

After 9/11, confusion over what exactly made up the core of the Towers became pretty extreme, from the BBC suggesting a single, solid reinforced concrete pillar for the core, to the 9/11 Commission Report suggesting no real core structures, to FEMA and NIST's Reports, which are most commonly accepted, and describe the cores as steel box columns only.

This confusion over what exactly made up the cores should be kept in mind when we are presented with photographs such as the below,



but for the sake of argument, it's probably easiest to assume that NIST and FEMA have presented accurate models, despite not releasing the construction drawings, etc.

Originally posted by Valhall


Right, it was steel. It had 2" thick by 16" wide tongue-and-groove gypsum planks that boxed in the columns.

In construction nomenclature it known as "Core board" it slips into a light gauge "H" shaped stud and is then pinned into place with drywall screws on 8" centers. Most core board assemblies I've seen installed consist of 2 - 1" layers, 1 - 1" layer in each throat of the "H" stud. Commonly these are used to make firewalls for mechanical shaftways such as elevator, return, exhaust and outside air shafts as well as provide fireproofing for stairwells.

In an event with fire only I can see these assemblies being effective in providing time for occupants to escape which is the job they are there for - Ie; 2 hour rating.

In an event with a pressure pulse such as an airplane strike I do not believe the assemblies would stay intact - they are only as strong as the floor - ceiling light gauge track or channel attachment.

The channels that studs are attached to are normally held in place by nails shot into concrete deck by a powder actuated tool about every 16 inchs or so. The nails themselves are quite strong individually and can take anywhere from 500 - 1000 lbs of pull before releasing from the spall formed in concrete when installed - however the head of the nail is rather small and has little bearing surface on the channels sheetmetal.

The force of pressure spread across the entire footage of one of these walls could easily result in failure without a direct impact - opening shaftways to fire spread floor to floor. Once opened the "chimney" effect would be tremendous on a building of such height as WTC 1 & 2.

The core column wraps having a much smaller surface area probably would have remained intact unless damaged directly by impact.

What this has to do with trusse's - I don't know but thought I'd add my 2 cents to this subject.

As far as trusses are concerned they were only as strong as their attachment points to the vertical members - its the failure mode of those points that would be critical to the question at hand.

If they were stronger than the trusses ability to hold weight or withstand fire deformation then yes I can see their effect on pulling in exterior columns in tension.

If they were weaker that supports "pancake" theory that much more.

Personally I think it was a combination of stong enough to stay intact with tension from truss deformation pulling in exterior columns until global collapse sliced them like a hot knife through butter.

Originally posted by Valhall

I read (on another thread on ATS) an account where a maintenance guy claims he got caught in some area in the core and 'cut his way through the sheetrock with a squeegee'...yeah, and bob's your uncle and the check's in the mail.

[edit on 8-4-2006 by Valhall]

The gentleman who allegedly did this was one Mr. Demczur. He was allegedly stuck in an elevator with 5 other people and used his squeegee blade and then the handle to cut/scrape through 3 layers of sheet rock. They are planning on putting the squeegee handle in a museum at the Smithsonian.

Source: www.smdp.com... (Scroll down to page 6)

[edit on 6-8-2006 by craig732]

Originally posted by craig732


The gentleman who allegedly did this was one Mr. Demczur. He was allegedly stuck in an elevator with 5 other people and used his squeegee blade and then the handle to cut/scrape through 3 layers of sheet rock. They are planning on putting the squeegee handle in a museum at the Smithsonian.

Source: www.smdp.com... (Scroll down to page 6)

[edit on 6-8-2006 by craig732]

I would say that if he was able to dig through 2 inch thick sheetrock in less than 1 hour with a squeegee...they need to put in the Smithsonian...right after they do an anlysis of what type of alien metal it was made out of.

Originally posted by Valhall

I would say that if he was able to dig through 2 inch thick sheetrock in less than 1 hour with a squeegee...they need to put in the Smithsonian...right after they do an anlysis of what type of alien metal it was made out of.

According to him and several of the witnesses (I don't think they ever interviewed all 5 witnesses) the sheetrock was not 2 inches thick. It was claimed to have been 3 layers of sheetrock.

I just got back from the engineering shop here at my job. The thickest sheetrock we have is one inch. I clamped 3 pieces of it together and was able to scratch a grapefruit size hole (the size of the hole the man claimed to have scraped) through it in under 10 minutes with a 1/4 wide piece of brass trim. (Sorry I have no squeegee here, but most industrial squeeges are made from brass and I think it was a pretty close match.)

Why do you doubt this man's story, and what does it have to do with the topic at hand?

The 2" thickness comes from the NIST report. These were special made planks with metal tongue-and-groove.

I find the report hard to believe - because I find the report hard to believe.

What does this have to do with the topic at hand? I have absolutely no idea...I'm not the one that brought it up. I'm the one that doubted it.

Originally posted by Valhall
The 2" thickness comes from the NIST report. These were special made planks with metal tongue-and-groove.

I may be mistaken, but I believe those 2" tongue-and-groove planks were positioned around the core columns themselves; not the elevator shafts.

Now that might be right. So the 2" planks were around the outside of the core columns and then within the core columns were the elevator shafts with an additional sheetrock layer of less thickness? Is that what you are saying?