Questions about Jim Hoffman

[CTM]

I have been working through the text of Jim Hoffman’s slide presention . (http://911research.wtc7.net/talks/towers/text/index.html ) I am filling in a lot of information that he has wrong, left out or has distorted as I am dealing with a truther who is pretty convinced that he has presented the real “truth”. When I got to this section I was kind of stumped because I cannot find any information to either deny this nor to support it. He thinks the blueprints support this but I looked at them through a link on this site (http://www.internationalskeptics.com/forums/showthread.php?t=78050&highlight=claims+arise+blueprints)
that showed them and I don’t see what he’s talking about . I capitalized the sections that are puzzling me.
“One, there were PERPENDICULAR TRUSSES INTERWOVEN WITH THE TRUSSES that you see. That would have unified the entire structure and you couldn't have had this chain reaction of unzipping around the building.”
“The perimeter columns were linked by horizontal spandrel plates, and the core structure was a HIGHLY CROSS-LINKED STRUCTURE that was EASILY CAPABLE OF SUPPORTING ITSELF (and several times the weight of the entire building). FEMA's report pretends that the towers would instantly self-destruct if the floor fell away. The key deception is to misrepresent the core as flimsy. They show the core columns at about a third of their dimensions. They don't show the CROSS-BRACING BEAMS.”
“Now note that these cores were extremely robust structures. They had 47 box columns each a yard wide, fabricated of steel 4 inches thick near their bases. They were abundantly cross-braced and anchored directly onto bedrock. They did not need the floor diaphragms for support.
On the slide he says, “The core structures were lattices, densely cross-braced.”
The core structures could have survived in a hurricane force wind BY THEMSELVES. They wouldn't have simply vanished if the floors collapsed.”
“And finally the domino-effect collapse of the floors diaphragms would have LEFT BOTH THE PERIMETER WALL AND CORES STANDING -- the floors would have slid down the cores like records on a spindle.”
So a few questions that I would want specifically answered are:
Could either the perimeter or the core stand all be themselves if there were no trusses joining them?
Were there “perpendicular trusses interwoven with the trusses”? I can’t imagine what these would have looked like and I haven’t seen anything like this in any diagrams or photos that I have seen. What would they have been perpendicular to?
What is he talking about when he says the core section had “cross-bracing beams” and “lattices, densely cross-beamed?
What do you think is the source of his claims? Is he just repeating someone else’s ideas or is he the original “thinker” here?
If there is anything else in these quotes that are incorrect could someone please point that out too.
Thanks for any help.

 

[Newtons Bit]

Answers

One, there were PERPENDICULAR TRUSSES INTERWOVEN WITH THE TRUSSES that you see. That would have unified the entire structure and you couldn't have had this chain reaction of unzipping around the building.

This is sort of correct. There were two way trusses at the corners of the buildings. The structural engineering purpose of this is two-fold:

1) Eliminate the need for truss girders thus keeping the floor-to-floor height of the building low. This allows more floors for the same height of building and thus more rent-able space for the same (roughly) cost.

2) Distribute the load evenly on both sides of the corner. A one-way truss system would only load one wall. This causes problems for overturning amongst some other complicated issues dealing with the lateral system that are too complicated to go into here.


In any event, they don't provide any strength to "unzipping" as it were that normal truss systems don't. Hoffman is talking out of his rear-end.

The perimeter columns were linked by horizontal spandrel plates, and the core structure was a HIGHLY CROSS-LINKED STRUCTURE that was EASILY CAPABLE OF SUPPORTING ITSELF (and several times the weight of the entire building). FEMA's report pretends that the towers would instantly self-destruct if the floor fell away. The key deception is to misrepresent the core as flimsy. They show the core columns at about a third of their dimensions. They don't show the CROSS-BRACING BEAMS.

Here he doesn't know what he's talking about. There is cross-bracing that connects that core columns together in the lower floors and I believe at the mechanical floors. The vast majority of the floors do not have this. It is not capable of supporting itself without the floors. A single floor loss would probably not be catastrophic, but multiple ones would. This is an issue with buckling, which truthers do not understand.

Now note that these cores were extremely robust structures. They had 47 box columns each a yard wide, fabricated of steel 4 inches thick near their bases. They were abundantly cross-braced and anchored directly onto bedrock. They did not need the floor diaphragms for support.
On the slide he says, “The core structures were lattices, densely cross-braced.

See above.

The core structures could have survived in a hurricane force wind BY THEMSELVES. They wouldn't have simply vanished if the floors collapsed.

This is patently false. The core was not part of the lateral resisting system. It would not resist any lateral force. This was a unique design of the time. Typically the "core area" where the bathrooms, stairs, elevators, etc are located is where the architects want the lateral resisting system. The reason for this is that the LRS's usually consist of concrete shear walls or braced frames. These prevent the nice large spacious windows that architects like putting in to view the world with. The WTC designers did something different and new.

And finally the domino-effect collapse of the floors diaphragms would have LEFT BOTH THE PERIMETER WALL AND CORES STANDING -- the floors would have slid down the cores like records on a spindle.

Heh, no. He needs to learn a little bit about a man named Euler and a man named Stanley.

I think I've already answered most of your questions. But Hoffman is another example of a man who doesn't know anything leading people who don't want to know anything. His entire work is argumentum ad dontknowwtfimtalkingabout.

I don't know if he's the original thinker.

 

[CTM]

Thank you very much Newton's Bits. You have been very helpful. Who are Euler and Stanley? If it's not too complicated what do they add to this?

 

[Myriad]

I think that when Hoffman talks about "cross-bracing beams" and "cross-linked structure" he's incorrectly referring to horizontal members connecting the core columns, and perhaps also the horizontal spandrels connecting the perimeter columns. These did exist, but they do not constitute "bracing" in the engineering sense. The way you can tell that the core was not designed to be able to stand on its own is the lack of any diagonal bracing on most floors. Only the mechanical floors, the corners, the floor trusses, and the hat truss had any diagonal members (perhaps also the ground floors, I'm not sure).

If Hoffman is so sure the core could stand on its own, perhaps he can point out an example of a freestanding steel framework structure that does not have continuous diagonal bracing all the way up, of any significant size and with comparable slenderness to the trade center tower cores. After all, if such a structure could stand on its own (and even resist hurricane-force winds!), it would be very handy and economical for many purposes and there should be lots of them around.

Respectfully,
Myriad

 

[SpitfireIX]

Thank you very much Newton's Bits. You have been very helpful. Who are Euler and Stanley? If it's not too complicated what do they add to this?

To save NB some typing:

From a Wikipedia article on buckling^WP:

In 1757, mathematician Leonhard Euler derived a formula that gives the maximum axial load that a long, slender, ideal column can carry without buckling.

I'm not sure who Stanley is (I'm just a lowly sophomore in mechanical engineering and CAD designer) but I think it might be this person.