The RMackey "Cross-Bracing" Lie

[Loss Leader]

TS1234, you're back? Didn't you say something about not posting anymore? Oh, here it is:

I will have no part of this forum until one of the following two things happens: Loss Leader takes it back and apologizes, or Loss Leader is permanently banned.

Did I miss my own apology?

Okay, for the record, I absolutely, catagorically, unreservedly do NOT apologize. I believe with all my heart in my prior postings and I reaffirm them as though they were fully set forth here.

Now, TS1234, you comining back to the forum absent my apology makes you a liar. If your pants are not, in actual fact, on fire than I sincerely believe they should be. Also, I do not apologize for the quip I made in the last sentence.

And the pictures you posted show diagonal cross-bracing for the cranes during construction. They were removed when construction was completed which was good for the tenants of WTC 1 and 2, seeing as the cross-bracing was blocking the elevator shafts.

 

[Bell]

Now, TS1234, you comining back to the forum absent my apology makes you a liar.

Touche...

 

[Brainache]

My daughter is 9 years old and one of her favourite DVDs is Barbie: The Princess and The Pauper. I actually bought a copy of this DVD and have therefore given money to Truthseeker1234 (yes I checked. Ace Baker wrote the song which plays over the end credits).

I should really learn not to let my kids bully me like that.

 

[TruthSeeker1234]

I was partly wrong, but mostly right. The crane supports were not part of the permanent structure.

My central point about cross-bracing is correct: The core structures were abundantly cross-braced, horizontally and diagonally. The notion that the core columns would deflect to the sides absent the main floor trusses, as asserted by Mackey, is still totally wrong.

Mackey clearly implied that the main floor trusses were the only means of lateral support for the core columns.

 

[Arkan_Wolfshade]

I was partly wrong, but mostly right. The crane supports were not part of the permanent structure.

My central point about cross-bracing is correct: The core structures were abundantly cross-braced, horizontally and diagonally. The notion that the core columns would deflect to the sides absent the main floor trusses, as asserted by Mackey, is still totally wrong.

Mackey clearly implied that the main floor trusses were the only means of lateral support for the core columns.

Unlike Architect, I am not an architect. Could you please provide a diagram, or photo with overlaid diagram, showing this cross-bracing on the core structures; and a link to some information detailing how such cross-bracing works?

 

[babazaroni]

Mackey clearly implied that the main floor trusses were the only means of lateral support for the core columns.

Why do you keep referring to floor trusses? These trusses linked the inner columns to the outer columns and had nothing to do with lateral support for the core except for being a part of the entire system.

Perhaps you mean the horizontal bracing these trusses were attached to?

Mackey has said several times there was diagonal bracing at key floors, such as the mechanical floor.

Here is the Wikipedia definition of a truss.

 

[DavidJames]

The core structures were abundantly cross-braced, horizontally and diagonally. The notion that the core columns would deflect to the sides absent the main floor trusses, as asserted by Mackey, is still totally wrong.

Could you provide evidence for the two claims above.

 

[chran]

Unlike Architect, I am not an architect. Could you please provide a diagram, or photo with overlaid diagram, showing this cross-bracing on the core structures; and a link to some information detailing how such cross-bracing works?

What he said.

 

[uk_dave]

My central point about cross-bracing is correct: The core structures were abundantly cross-braced, horizontally and diagonally.

ermmm...I'll ask again:

Where did they put the doors?

 

[babazaroni]

My central point about cross-bracing is correct: The core structures were abundantly cross-braced, horizontally and diagonally. The notion that the core columns would deflect to the sides absent the main floor trusses, as asserted by Mackey, is still totally wrong.

As the tops of the towers tilted, there were intact core columns and some missing core columns. The horizontal bracing at each floor level were not designed to hold the inner core stable while the tilting portion leveraged against the asymetrically damaged core. This would cause a 3d twisting which would cause catastrophic failure.

 

[Minadin]

Where did they put the doors?

Well, it's possible to cross brace in some structures in such a way that not every bay has / needs the bracing in it. So, you might have a series of bays in a building that looked like this:

|X| | | | |X|

Where it's just on the corners / sides, or at least not in every bay. Also, diagonal bracing can be, in practice, a little bit easier to work with as far as punching through, because it usually allows openings on at least one side. For instance, we recently had to get our structural engineers to change all their cross bracing in a major medical office building from:

| | |X|X|X|X| | |

to:

| | |/|/|\|\| | |

Just so that we could get tenants into the east half of the building. (mutters about engineers under his breath)

 

[Belz...]

Touche...

Actually it really could be just a case of changing one's mind, in this instance.

 

[Belz...]

My central point about cross-bracing is correct: The core structures were abundantly cross-braced, horizontally and diagonally.

Did you miss Mack's quote of the report on this subject ??

 

[Bell]

Actually it really could be just a case of changing one's mind, in this instance.

What mind?

 

[tacodaemon]

It's pretty simple. Mackey says that the floor trusses were the only cross-bracing that the core had. Even ignoring the diagonal braces, we still have an independent floor system in the core which provided bracing at every story. Mackey claims that if the floors broke away from the core, the core columns are "free to deflect to the side". It's clearly false. Mackey is too smart for this to be a mistake. The reason for the lie is that we are supposed to imagine that, without the floor assemblies, the core structure would just fall apart. This is why the 9/11 commission characterized the core as "a hollow steel shaft".

Yes, you've discovered the amazing secret that the service cores of the Twin Towers had floors. In fact, I remember using the elevators and a men's room in the core of 2WTC and I didn't have to levitate across a 110-story chasm to get to them. That's quite a blistering exposé you've brought us.

 

[uk_dave]

Yes, you've discovered the amazing secret that the service cores of the Twin Towers had floors. In fact, I remember using the elevators and a men's room in the core of 2WTC and I didn't have to levitate across a 110-story chasm to get to them. That's quite a blistering exposé you've brought us.

The mens room was in the core? hmmmmm suspicious..... C4 in the wc pans, detonator in the cistern...... where's christophera?

 

[T.A.M.]

I was partly wrong, but mostly right. The crane supports were not part of the permanent structure.

My central point about cross-bracing is correct: The core structures were abundantly cross-braced, horizontally and diagonally. The notion that the core columns would deflect to the sides absent the main floor trusses, as asserted by Mackey, is still totally wrong.

Mackey clearly implied that the main floor trusses were the only means of lateral support for the core columns.

The world is flat

The earth is the center of the universe

There is a sasquach

Aliens have visited earth, and taken some people into their ships

My house is haunted....

TAM

 

[Belz...]

What mind?

It IS just a theory, after all.

 

[CurtC]

My central point about cross-bracing is correct: The core structures were abundantly cross-braced, horizontally and diagonally. The notion that the core columns would deflect to the sides absent the main floor trusses, as asserted by Mackey, is still totally wrong.

And you are aware that horizontal bracing is not very effective at keeping columns from deflecting to the sides, right? The fact is that they can still deflect to the sides all together, and in a very tall, narrow structure would not be enough. Diagonal bracing, of which there was very little in the towers, does a good job of that. Of course it wasn't needed becuase what really kept the core columns from sideways motion was that they were held in place by the perimeter columns, connected via the floor trusses.

 

[rwguinn]

And you are aware that horizontal bracing is not very effective at keeping columns from deflecting to the sides, right? The fact is that they can still deflect to the sides all together, and in a very tall, narrow structure would not be enough. Diagonal bracing, of which there was very little in the towers, does a good job of that. Of course it wasn't needed becuase what really kept the core columns from sideways motion was that they were held in place by the perimeter columns, connected via the floor trusses.

To be more concise:
Diagonal bracing is effective in resisting deflections only for in-plane forces. Out-of-plane forces result in out-of-plane bending.
By the way things work, it does not take much (relatively speaking) to prevent column buckling if the lateral forces are small when compared to the area moment of inertia.
at 200 feet per side, the area moment was huge! ((12*200)^4/12)(in^4) The entire purpose of the floor was to tie the inner and outer columns together, making the building one huge beam. The outside walls were the shear panels making the sides work together.