Slide #24 - Con Ed Substation

Congratulations Are In Order

With this slide, Richard Gage has done something truly remarkable. He has included a slide which contains no falsehoods or material misrepresentation of fact!

It's true: 7 World Trade did indeed span an existing Con Ed electrical substation. Gage also reproduces a few elevation drawings from the FEMA report, which show the location of this building relative to the 47-story skyscraper built above it.

It would have been nice if Gage had reproduced this rendition from NIST, which gives a much clearer view of how large this building loomed in 7 World Trade's footprint:

Yes, that large grey box is the Con Ed substation. It's the reason that the core columns were slid over into the southwest of the building, and why the easternmost columns 79, 80, and 81 are further away from the rest.

But beggars can't be choosers. I'm just so pleased to be able to say that Gage finally got a mostly truthful slide into this presentation.

Floors Five and Seven

Allow me to take this moment to explain a further oddity to 7 World Trade's structure. Because of this necessary asymmetry in the core column arrangement, you might wonder how the building supported itself. How could these oddly placed column support the building?

Floors Five and Seven were taken up almost completely with a diaphramatic structure to safely redistribute the various loads of the 40 floors above them into this off-center arrangement of core columns.

Both floors had a more massive floor slab than any other floor. Floors 8-45 had a 5.5 inch slab of metal and concrete. Floor 7's slab was 5 inches of concrete and 3 inches of metal decking, for a total of 8 inches, and Floor 5 had a whopping 11 inches of concrete with 3 inches of metal, for a total of 14 inches.

The 5th floor slab was 11 in. of 3,500 psi normal weight concrete on top of a 3 in., 18 gage composite metal deck for a total slab thickness of 14 in. The slab was heavily reinforced, with #7 rebar at 12 in. spacing for top reinforcement in both directions and #9 rebar at 12 in. spacing for bottom reinforcement that acted as additional diaphragm chord reinforcement in many areas. This floor also had 36 ksi steel WT sections (W, or wide-flange, sections cut in half to look like a 'T' section) embedded in the 11 in. concrete slab above the deck. The WT sections were designed to act as a horizontal truss within the plane of the floor between the perimeter and core columns (see Figs. L-10 and L-11).

Both floors worked together to provide what I call a "foundation in the sky" for the rest of the building, a foundation that under the extreme conditions of September 11th would prove to be quite vunerable.

Transfer Trusses #1 and #2

In all the dense network of trusses between these floors, I want you to notice two crucial transfer trusses:

This isn't all of the network of trusses and girders in floors five and seven -- just crucial structures. I've added some commentary to this drawing from NIST, and I've got arrows pointing to the transfer trusses I want you to focus on.

Because we are dealing with these transfer trusses a lot, I'm calling them Transfer Trusses #1 and #2. I've shown you these trusses before, but I didn't point them out specifically. Let me show you again:

Transfer Trusses #1 and #2 are highlighted in grey there on the right of the lower diagram (they are numbered oppositely of my numbering).

As you can see, Transfer Truss #1 was directly in the path of the collapsing third of the building interior, including the east mechanical penthouse itself. Transfer Truss #2 is very close to being in the line of fire itself.

And if you look at NIST's Figure L-18, you can see that some of the crossbracing for these trusses is underneath the east mechanical penthouse. In both cases, it was crossbracing meant to keep the building's interior from sliding to the east.

In the last slide, I pointed out that the west penthouse slid into the building from east to west, showing that the columns below were failing from east to west. This is the most probable reason why that was happening. As the building's interior was deprived of this crucial support, the mass of Floors Five and Seven could slide to the east.

Once this shift to the east began, the final stage of collapse was inevitable. With the additional lack of support from the damaged southern perimeter, the entire building became a massive train wreck crushing itself up from the ground, spilling out to the south, then to every direction. Because of the precautions of Chief Daniel Nigro, first responders had been pulled away from this severely damaged building, and no one was killed when 7 World Trade collapsed.

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