WTC7: Does This "Look Like" a Controlled Implosion?

Joe Hill

Member
@Joe Hill Presumable the structural failures could be initiated by destroying key components and initiating a run away progressive failure. So for example the support for TT1 if disabled...
This thread isn't looking for what initiated collapse, or what transfer trusses and core columns were doing.
We are asking if there's any way controlled demolition caused the east part of the perimeter frame to fall over at it's onset.
We know the perimeter frame was standing in a visibly static position, then lurched over at the instant the west penthouse initiated it's descent. Does that look like controlled demolition? How could controlled demolition make the structure move like that?
1412547701_bowingnorthface2.gif
 

Jeffrey Orling

Senior Member
@Joe Hill
I don't know and I believe that all the observed movements were caused by INTERIOR structural failures... including the fold in the north face.

The motion also might be a DIPPING of the face which would appear as folding... or both.

The cause was the the timing if the interior failures which led the the floor plates separating from the east face ahead of the rest of the facade. The collapse form is likely a matter of mass distribution and the geometry...

So if CD initiates failures low down in the east side the collapse form will look as observed.

An engineered demo sets up a sequence of axial failures to control as much as possible where the mass falls. Often the scheme will structurally hollow out the building and the slabs remain connected at the facade and act like cantilevers and cause the face to fall inward. The demo is engineered based upon the structural design.
 

Jeffrey Orling

Senior Member
It's hard to sketch the "sequence" in a single image. And it hard to know. All we can see is the north and west face. But for sure they did NOT lag in the collapse.

1. failure in axial support in East region
2. east side floors collapse... EPH comes down,
3. floor collapse progresses westward involving entire foot print
4. initial floor debris piles up in east side bulges outward from the foot print causing 7 stories of facade at east facade to collapse/buckle
5. progressing floor debris piles up in balance of foot print pushes outward from the foot print causing seven stories of facade at balance of perimeter to collapse/buckle.
8. Facade descends 100+ feet at free fall and then slows when 8th floor of facade encounters ground and resistance where it is crushed.
9. facade begins to break apart in to large areas and top sections are seen on the top of the debris pile.
COLLAPSE SEQUENCE_page1.jpg
 

Joe Hill

Member
How did a gravity collapse cause that motion?
answer: It could happen in a demolition or gravity collapse.
I've tried to figure if there is any way for controlled demolition to make the east part of the structure lurch northerly as it did, instantaneously when the west penthouse initiated it's descent. Removal of the lower NE is the only way I can think of for controlled demolition to make it move thus, but we see no downward motion of the NE corner. What other way is possible? Failure to provide an answer means no, it did not look like a controlled demolition.
 

Jeffrey Orling

Senior Member
The buildings "parts" collapsed... which means that what wast supporting those parts lost its stuctural /axial capacity. Id the support lost was "asymmetrical" a moment will develop and the part will tip as well as fall. Parts were interconnected... the building was no a structure of jenga blocks.

What I see is:

The EPH collapses and there are clues that it and the floors/structure below it collapsed down inside the tower

What I can't see but what I suspect is:

That collapsed east side material began a progressive failure east to west low down in the building and likely involved the massive transfer structures on floors 5 -7. This led to the "undermining" / destruction of all axial load paths inside the tower..

and tI can see the roof structures collapse as the facade starts to drop... as FF

It drops 100+ feet with no resistance so it accelerates at about G. Then the "shell",, curtain wall and moment frame hit ground and slow in a crush up.

The east side of the north face does no LURCH north... it is pushed north because of the asymmetry of the plan form and that the mass collapse began there AND it was supporting a 2 way slab.

++++

A CD would have to imitate the sequence of the initial failures (wherever they were in the east side)... the so called straw that broke the camel's back. It may require... as CD often does... pre weakening of beams and columns to control / direct the way the collapse progresses.
 
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