Did a pair of <3.5 quakes knock down WTC7?

[realpolitic]

I bought the story that the collapse of the Twin towers caused WTC7 to collapse. It seemed obvious. Then I thought of what causes buildings to collapse. The dramatic pictures usually occur when there is a 6.0 or greater quake. That's equivalent to 1 megaton, much more than the force of the collapse.

How much force was generated by the collapse of these 1360 ft buildings? The average distance debris fell is about half the height of the buildings 700 ft. The weight of each tower 1 billion pounds, so the force is 700 billion foot-pounds, or 220 tons of TNT. It's equivalent to a 3.5 quake. Now some of it's lost because it is so small it takes minutes to hit the ground, some more is lost, because as the ground is bouncing up as the debris pushes it up. If 10% of the energy is transmitted as a quake then it's a 2.8 quake. Sesimometers registered 2.1 and 2.3, or the equivalent of a single floor.

WTC7 was half a block away from the other towers, and 9/11 was described as a beautiful day, ie not lots of wind. Had some debris blown onto WTC&, New York State has building codes to protect against nasty blizzards upstate(my father was an architect).

I didn't want to accept the they of intentional demolition, eigther, does anyone have a plausible hypothesis?

[Provost Harrison]

I thought the main problem was actually the sheer damage caused to the groundwork by the collapse at those points...which affected the entire area...

[Winston]

Also consider the fact that President Bush had actually taken office less than a year before.

[JohnT]

The squibs! Don't forget the squibs!

[Q Classic]

Actually, Nostradamus predicted it in one of his tracts. Don't believe me? Go read it yourself. You'll see...

[Provost Harrison]

I thought he'd just predicted The Lord Of The Rings

[niDe]

realpolitic have you seen the Loose Change documentary?

[Berzerker]

I thought the main problem was actually the sheer damage caused to the groundwork by the collapse at those points...which affected the entire area...

Yup, and the epicenter was so much closer. I've been in enough quakes to know a 3.5 or 2.8 is noticeable but not much else. I cant imagine standing half a block away from that and getting the same impact.

anyone have an aerial or map of the buildings in that area and the ones that fell? If closer ones survived that would be interesting...

[Urban Ranger]

Originally posted by Provost Harrison
I thought the main problem was actually the sheer damage caused to the groundwork by the collapse at those points...which affected the entire area...

Didn't WTC7 stand on its own piles?

[Provost Harrison]

You tell me

[Urban Ranger]

I thought that would be the case, although I never had a chance to look at the World Trade complex structurally.

If that is the case, i.e. the tower itself got piles to support its entire mass (plus a nice margin), it shouldn't have collapsed that easily.

[Vince278]

Originally posted by Q Cubed
Actually, Nostradamus predicted it in one of his tracts. Don't believe me? Go read it yourself. You'll see...

Amazing how many predictions show up after something happens.

[JohnT]

I'm thrilled that people are adding earthquakes to the mixture of things that occurred in NYC on 9-11. The Oliver Stone movie should be more exciting and convoluted than JFK.

However... those poor buildings didn't stand a chance, what with the moslems, Dubya Bush, the neo-cons, the FBI, CIA, Israel, Allah, God, Saddam Hussein, Saudi Arabia, God, Halliburton (you just know they're involved!) and now Mother Earth all gunning for them that fateful September morn.

[GePap]

WTC7 was accross the street from the North Tower. It is rather plausible that debris did impact the building- after all, even if windy, when we are talking about steel and cement the wind is not going to be the main reason for debis going elsewhere. And debris did make it pretty far- the Winter Garden and the World Financial Center all took nasty hits, and they were farther from the towers than WTC7.

So I can see the building being weakened by the debris from the towers, then weakened further by the collapse of the towers, and finally coming down a few hours later.

Its sad that the location of WTC7 is the only one that has been rebuilt (the new building is almost finished) while on the south side of ground zero the Deutsche Bank building remains abandoned and shrouded, waiting for demolition.

[Darius871]

NIST researchers now support the working hypothesis that WTC 7 was far more compromised by falling debris than the FEMA report indicated. "The most important thing we found was that there was, in fact, physical damage to the south face of building 7," NIST's Sunder tells PM. "On about a third of the face to the center and to the bottom--approximately 10 stories--about 25 percent of the depth of the building was scooped out." NIST also discovered previously undocumented damage to WTC 7's upper stories and its southwest corner.

NIST investigators believe a combination of intense fire and severe structural damage contributed to the collapse, though assigning the exact proportion requires more research. But NIST's analysis suggests the fall of WTC 7 was an example of "progressive collapse," a process in which the failure of parts of a structure ultimately creates strains that cause the entire building to come down. Videos of the fall of WTC 7 show cracks, or "kinks," in the building's facade just before the two penthouses disappeared into the structure, one after the other. The entire building fell in on itself, with the slumping east side of the structure pulling down the west side in a diagonal collapse.

According to NIST, there was one primary reason for the building's failure: In an unusual design, the columns near the visible kinks were carrying exceptionally large loads, roughly 2000 sq. ft. of floor area for each floor. "What our preliminary analysis has shown is that if you take out just one column on one of the lower floors," Sunder notes, "it could cause a vertical progression of collapse so that the entire section comes down."

There are two other possible contributing factors still under investigation: First, trusses on the fifth and seventh floors were designed to transfer loads from one set of columns to another. With columns on the south face apparently damaged, high stresses would likely have been communicated to columns on the building's other faces, thereby exceeding their load-bearing capacities.

Second, a fifth-floor fire burned for up to 7 hours. "There was no firefighting in WTC 7," Sunder says. Investigators believe the fire was fed by tanks of diesel fuel that many tenants used to run emergency generators. Most tanks throughout the building were fairly small, but a generator on the fifth floor was connected to a large tank in the basement via a pressurized line. Says Sunder: "Our current working hypothesis is that this pressurized line was supplying fuel [to the fire] for a long period of time."

WTC 7 might have withstood the physical damage it received, or the fire that burned for hours, but those combined factors--along with the building's unusual construction--were enough to set off the chain-reaction collapse.

http://www.popularmechanics.com/scie...tml?page=1&c=y