September 11 conspiracy theorist offers prize
 

NEW YORK (Reuters) - Jimmy Walter has spent more than $3 million (1.5 million pounds) promoting a conspiracy theory the September 11, 2001, attacks on the United States were "an inside job" and he is offering more cash to anyone who proves him wrong.

The millionaire activist is so convinced of a government cover-up he is offering a $100,000 reward to any engineering student who can prove the World Trade Centre buildings crashed the way the government says.

"Of course, we expect no winners," Walter, 57, heir to an $11 million fortune from his father's home building business, said in a telephone interview from California on Wednesday.

He said a panel of expert engineers would judge submissions from the students.

Next month, he also launches a nationwide contest seeking alternative theories from college and high school students about why New York's World Trade Centre collapsed. The contest offers $10,000 to the best alternative theory, with 100 runner-up awards of $1,000. Winners will be chosen next June.

The World Trade Centre's twin towers were destroyed after hijackers slammed two commercial airliners into them. The attack in New York killed 2,749 people.

Various official investigations give no credence to Walter's theory. A September 11 commission spokesman did not return calls seeking comment.

Walter insists there had to be explosives planted in the twin towers to cause them to fall as they did, and also rejects the official explanation for the damage done at the Pentagon (news - web sites).

"We have all the proof," said Walter, citing videotapes and testimony from witnesses.

"It wasn't 19 screw-ups from Saudi Arabia who couldn't pass flight school who defeated the United States with a set of box cutters," he said. He dismissed the official September 11 commission report, saying, "I don't trust any of these 'facts.'"

Walter has spent millions of dollars to bolster support for his case, running full-page ads in The New York Times, the Wall Street Journal, The New Yorker and Newsweek, as well as alternative newspapers and 30-second TV spots.

He points to a Zogby poll he commissioned last summer that showed 66 percent of New Yorkers wanted the 9/11 investigation reopened.

Walter has spent about 30 percent of his net worth on his efforts.

"I am a patriot fighting the real traitors who are destroying our democracy. I resent it when they call me delusional," he said.

He's a useful idiot.

Notice this idiot is spending his father's hard-earned money. He probably hasn't earned a dime his whole life. Also, it strikes me that there's a marked difference between providing proof and convincing an unhinged idiot.

That's how we churn inherited wealth back into the system. Get some freak to blow the legacy money on stupid ventures.

We should put our great minds to work and usbmit a proposal to him about UFO's being ivnvolved. I mean, a UFO with exotic materials probably hit the Pentagon and that's why there's not enough debris. The military scooped it up and trucked it piecemeal to Area 51. I'll bet we can make some pictures that prove it is linked to the Elders of Zion and the Illuminati.

I discussed the early analysis by the two MIT engineers Eagor and Musso with an engineering friend of mine last week. He agreed that there was nothing in their analysis which explained why the core of the two towers fell.

Did anybody look into propagation of harmonic resonances? I'm thinking that the collapse was aided by vibrations as the floors collapsed. The floors are regularly spaced. As one floor pancaked to the next, the vibration would travel through the structural steel at a faster rate than through the air (sound travels with speed directly proportional to teh density of the medium through which it travels). It would reach the ground and reflect back up the tower.

At some point in that collapse, the vibration wave train projected downward by the collapse would coincide with the returning wave. I wonder how many harmonics the building would have? I'll bet that if you solved for the velocity of sound through the structural steel and the rate of floor collapse that you would end-up with a series of nodes in which energy would build faster than the floors collapse, weakening them before the tower collapsed onto them. You would then have a general failure instead of the pancake stack model.

I don't see the need for any conspiracy theories. The floor the plane crashed in was sprayed with tons of jet fuel, causing a catastrophic fire. Iron loses it's strength as it gets heated, the floor collapses, the building pancakes.

The computer models I have seen (I think it was the FEMA study) did not show the steel in the core reaching a temperature high enogh (450c) to lose its structural properties. I think the highest temperatures were 175c. But even if the core steel at the level of the fire failed, why did the whole core come down?

How did the core, which is essentially as long pillar of continuously joined steel, collapse? The floor steel yes. The core??
I don't know about the harmonics.

I saw something about this and they said it was welds and bolts that gave way not the actual I-Beams.

The floor was not designed to hold a 757 either.

From what I have read, you're correct. The connections between the steel floor joists and the inner core and outer load bearing walls gave way. But that still leaves the question of how the core itself could come down. In that scenario, each floor disconnects from the external walls and internal core and pancakes down. But why did the core and outer walls come down?

Here's a link to the early report from MIT: (I'm typing it in, so I hope it works)

http://www.tms.org/pubs/journals/JOM/0112/Eagar/Eagar-0112.html

As Botsnst points out, all kinds of forces are in play. The floors above the fire had tremendous weight. I fail to see how anyone could estimate the temperture of the fire - there were combustables, hot-burning fuel and even more importantly, oxygen available in abundance. In addition, at that altitude, there may have been wind drafts that acted like bellows in a black smith's fire, or these drafts may have been created by the tornadic effect one sees in firestorms. If one raises the estimated temperture of the fire, the collapse of the building becomes obvious. The core would snap due to lateral forces as the building swayed at that point. After that, gravity would do the rest. As in most science, the most obvious theory is the one that is most likely true. A plane hit the building. A fire insued. The building collapsed. The building collapsed because of the fire and structural damage, caused by a plane hitting it.

I was an ironworker for a number of years. Essentially all these buildings are tied together with pins - either bolts or hot rivets, but they are pins none the less. If it was all welds, the building would be too stiff and snap like a toothpick from harmonic forces in the earth and.or wind shear. Bolts and pins have a little give to them - they can microscopically twist and turn to accept these forces. The "core" is the same - it is not some continous piece of iron, plates and pins hold it together. At strategic places, the girders and beams are connected by "moment welds" - super strong welds placed there to hold the building together in the event of an earthquake. This was not an earthquake.

That brief was written in 2001. Have they written a follow-up in which the points they raised are addressed?

Also, my favorite, harmonics, isn't mentioned. Remember the Tacoma Narrows. http://www.enm.bris.ac.uk/research/nonlinear/tacoma/tacoma.html

A fully loaded 757 weights 250,000 pounds.

A lot of that weight would have been quickly consumed. Aluminum goes up quick. My personal theory is the fuel tank ended up between the central core uprights - the super critical four central columns. They don't have to break to cause a catastrophe, they just have to bend a little. When they bend, the floors above drop a little, and a gravitional force is created that accelarates and intensifies the bending, until the tensile point of the steel is reached, and it breaks. A combinition of on board oxygen containers and a bellows-blast of air thru the hole made by the plane into this fuel heated those four columns until they could bend a little. The slight bending would have created a force on the central columns from the upper floors that looked like this \ /
. As the upper floors sagged in the middle, all these forces would have been pushing in on the central columns from the top and sides. When they snap, the mega tonnage from the above floors now drop feet, not inches. Fageddaaboutit.

Weight hell, F=ma. That's where the action is.

It would look like this:

__
__ <- upperfloors
__
\ / <- floor plane hits, outer walls move toward center as four center columns bend inward towards the center
\ /
\ /
\ / <- all the way down

I still think it is funny that if someone suggests that a conspiracy got us into the war on terrorism they are automatically a nutcase.

Talk to people from around the world and ask their views on this issue.

If there are no conspiracies then we should not have laws against them, but we do, and we need them.

Did conspiracies lead to the US entry into the Spanish-American war, WWI and WWII?

Was the Cold War a conspiracy?

Do you think that people in those eras were called nutcases when they suggested conspiracies were involved?

Truth is that history and the present are fraught with conspiracies. Big money has been doing it to the little guy throughout history and it will not end any time soon.

Why don't the importers that are getting immensely wealthy from globalization pay their share of taxes here in the US?

I can see some of the central columns failing that way. But there were around 20 central steel columns in that building which you note are joined together with rivets, bolts and welds, all the way down to the foundation. I can see where the floors collapsed and the upper section came down on the bottom section but it still is a mystery to me as to why the central core basically disintegrated. Are you saying that each successive floor of the central columns collapsed inward? Why would they do that?

I was wrong on 2 counts. There are around 40 steel columns and it was NIST and not FEMA that modelled the temperatures they got to. On the thread below are a couple of pictures from the NIST report showing the temperatures. If you scroll to the next page of the thread, there is also another model of the damage done by the planes and the various temperatures:

http://www.libertyforum.org/showflat.php?Cat=&Board=consp_911&Number=293095626&page=0&view=collapsed&sb=5&o=21&part=24&vc=1&t=0

On the following page of the thread is a picture of the buildings being built so you can see the steel core:

http://www.libertyforum.org/showflat.php?Cat=&Board=consp_911&Number=293095626&page=0&view=collapsed&sb=5&o=21&part=26&vc=1&t=0

Every two floors or so they are spliced together using 1" steel plates that have hundred holes drilled in them, with matching holes in the column itself. Torque bolts or rivets are bolted together in the holes. If the weight above is more than the splice can hold, the plates snap. Think of a 2x4 standing upright, and you placed more weight than it could hold, compared to two 2x4 spliced together in the same arrangement. The single piece will support a great deal of weight, and when it collapses, it will collapse at the weakest point in the wood. The spliced piece will collapse with a lot less weight, even more readily if the weight above is swaying and places lateral forces against it, and it will always collapse at the splice. When it does, it pulls the exterior walls and floors down with it, creating a tremendous load on the next floor. Next splice snaps. Ad infinitum.

Once one goes, the exterior walls of the floors above become part of the downward gravitational push on the center columns.

Also, whatever the physics are of a 250,000 lb plane, as Medmech mentioned, would have been a tremendous lateral force. If the plane's fuel tank had burned on column splice points that had absorded that kind of impact, the scenario for a mere bend instead of break in the intial event becomes even more likely. It takes less energy to cut a piece of steel with heat after it has been bent. Since the splices run about every other floor, the probablity of the plane hitting on a floor with them is a coin toss. I would bet both buildings won.

Skull plumbing
 

Assuming a velocity of 300 mph and converting to SI, and applying 1/2mv^2

E = .5 X 113,000 X 480000^2 = 1.3E^16 joules

That's some big joules floating around in there. Where did they all go?

Well some of the energy got blasted out of the building on the opposite side. Lets say 1/2 of the mass passed through the building at a conserved velocity (this is overly optimistic. I'll bet less than 10% of the energy was dissipated out of the opposite side of the buildings).

E = 7E^9 joules left in the building. So excluding the fuel ignition for now, we have to conserve the energy of that airplane. We have a billion joules to get rid of. Where are we going to put it?

Well, some of that energy was dissipated smashing cubicles, monitors, filing cabinates, walls, beams (hroizontal and vertical), chairs, tables, and oh yeah, people. So I have no idea what the mass was of the floors that got struck, but lets say it exactly equaled one-half of the mass of the aircraft. Well, then that allows half of the mass of the aircraft (or if elastic, an equivalent mass of material from the building) to continue at velocity through the building and out of the other side. But we still have to wonder what happened to a billion joules or so.

So lets change all of that kinetic energy directly into heat. How much heat is released in the (say) one second it took 1/2 of the aircraft to completely dissipate its energy (recall that the other half went flying out of the other side, so we don't have to worry about it any more).

Q = m (t1-t0) Cp
rearranging to solve for temp change

(t1-t0) = Q/(mCp)

(t1-t0) = 7E^9/55,000*450 (spec heat of iron)
(t1-t0) = 200 deg C.

That's probably a low estimate since I flung more material at high velocity out of the building than probably actually got flung. OTOH, I assumed perfect energy transferrence from the aircraft to a solid iron object. That's obviously over-optimistic. But I'll bet it's not a bad lower boundary.

So into every part of those impacted floors of that building we change the temp from say 22C to 222C. This will not melt the beams, but it will soften them a bit and it will ignite all kinds of flammable debris. Including high-velocity keorsene-type fluids. Jike JP-4 or 5 or whatever they use. That high velocity fluid will become aerosol and ignite quickly and spread everywhere. This will also raise the temp.

Now if all this happened on the top 2-3 floors, it probably wouldn't have collapsed the building. Even if the structural steel softened the mass of the upper floors probably wouldn't be sufficient to collapse the floors below.

But the planes hit 10 or 20 floors down. There was lots of heavy steel and concrete above. the structural steel at the point of impact gets a cheerful reddish color by the heat of buring fuel and debris. Perhaps not melting, but you know steel bends when it is heated. Especially if its holding a 20 story building above it.

The steel beams deform and instead of the building being pulled by gravity against a tall column of steel supports, it now is pulled against a column that is somehwat softened and a bit deformed. If you push directly against a cold rod of steel you cannot bend it. But if you heat it at any point and then push, it will deform. Once it starts deforming, it bends quickly.

Now the whole force of the upper floors drops say, 3 meters at the force of gravity. If we knew how much teh upper floors weighed, we could guess at how much energy was carried by that accelerating mass. E = mgh.

So the resisting floor and columns below have to bear the building accelerating downward. Bam, it hits. A shockwave proceeds down the rigid steel column at the speed of sound in steel (6,000 meters per second, about). It hits the ground and some is reflected back up the column. Lets say the ground is 200 meters below so the sound wave takes about 0.05 seconds to return. It gets to the top and wiggles the top like crazy, disbursing most of its energy wiggling up there but some will also have been absorbed along the way by other floor--vibrations.

Lets see, if distance traveled under gravity is = 1/2 g t^2 then t = sqrt(2y/g). Using my 3 meter distance between floors we get about 0.7 sec.

Meanwhile, the resisting floor, weakened by heat, gives way which slowed the upper floors a bit but not much and they drop another three meters. Bam. Another shockwave is sent downward at the speed of sound but it has 3 meters less distance to travel while the building is accelerating under gravity minus the resistence of the floors.

Calculus rears its ugly head.

I think you catch my drift. At some descent time the shock wave going up and down will amplify each other. These nodes and antinodes will occur up and down the building. they are extremely high energy waves hammering and weakening each joint as the building descends. Thus each successive floor will be less resistent than the previous.

Worse, concrete is very resistent to pressure but not resistent at all to vibration.

And so on.

I was patiently waiting for B, to provide the math. Whether it's jets or bird poop your the man. I could've done it but I have things to do before Monday (the time it would take me to do it).

It's a pleasure to know someone as brilliant as you.

[QUOTE=Botnst]Now if all this happened on the top 2-3 floors, it probably wouldn't have collapsed the building. Even if the structural steel softened the mass of the upper floors probably wouldn't be sufficient to collapse the floors below.
But the planes hit 10 or 20 floors down. There was lots of heavy steel and concrete above. the structural steel at the point of impact gets a cheerful reddish color by the heat of buring fuel and debris. Perhaps not melting, but you know steel bends when it is heated. Especially if its holding a 20 story building above it.
The steel beams deform and instead of the building being pulled by gravity against a tall column of steel supports, it now is pulled against a column that is somehwat softened and a bit deformed. If you push directly against a cold rod of steel you cannot bend it. But if you heat it at any point and then push, it will deform. Once it starts deforming, it bends quickly.
QUOTE]

I think if you look at the NIST data on the temperature of the columns posted in the link earlier, it indicates that no columns approached 450C which is when steel begins to soften (according to the original MIT paper).
So, I guess a key issue is whether the fire was hot enough to raise steel to the temperature at which your hypthesis would come into effect or not?
The MIT guys combine your hypthesis with the idea that the temperature was not high enough to soften steel but high enough to distort the floor joists and cause them to fail. But this doesn't account for the core failure.

Well, I'm just trying to give an old ironworker's view. I believe the best explanation for why they can't explain it is that the temperature calculation is in error. I think the fuel tanks on those jets stayed more or less intact, took out the weaker columns with help from the jet, and became lodged in the four central core columns and burned. I bet the splices were at the tip of the fire, and and snapped on the floor above where the plane hit. Oxygen tanks from the passenger's compartment or wind forces, something like that raised the temperture of what had to be one hell of a fire in the first place. They also could have been wedged in the elevator shafts, further increasing the available oxygen. The bottom of those things are reinforced like crazy in case they have to belly land those things. I bet very little fuel leaked out of the bottom and the thing just sat there and burned, and burned with enough intensity to begin the chain reaction. My problem with the harmonic forces theory, while I am sure they played a part in the twisting and swaying that made the plates snap, is that I think most of those forces would have been more or less instanteous. Those buildings burned for about what? ten minutes before they came down. Fire and iron. Just my opinion.

I think one stood for 58 minutes (the second one hit) and the other for about an hour and half. That's one of the problems with the jet fuel fire hypothesis. I believe most people think the jet fuel burned early in the events (in fact some people say that the huge fireball that occurred when the second jet hit the second tower consumed a lot of the jet fuel itself) and the subsequent fires were just the contents of the building burning.

The tape recording of the firemen who arrived at the 78th floor of the second building states that they saw two fires that could be extinguished with two hoses. They apparently were not witnessing an inferno moments before the building collapsed.

[QUOTE=kerry edwards]Gee, I wouldn't base either support or rejection of the hypothesis on my ballpark (maybe solar system!) calculations. I hoped that what I wrote would get the civil engineers wandering about to pay attention and tighten-up my assumptions and methods. This is definitenly one of those cases when I know my 'Botanist' does not equal a civil engineer's 'P.E.'

I'm most curious about whether or not I parameterized the event appropriately.

For example, it might be interesting to estimate teh actual amount of debris ejected on the far side of the building. Also, teh amount of energy dissipated in the sway of the buildings. I should think a really careful study by appropriately educated, objective analysts would have been done since the paper you cited (2001). I have never cared enough to enquire. I'm betting there are several PhD dissertations on that subject.

Funny you should mention that. I found an MIT study, although it is not as current as what you would like, but it reaches the same conclusion that I, a mere x-ironworker reached. Here is my favorite highlight:

"However, the building was not able to withstand the intense heat of the jet fuel fire. While it was impossible for the fuel-rich, diffuse-flame fire to burn at a temperature high enough to melt the steel, its quick ignition and intense heat caused the steel to lose at least half its strength and to deform, causing buckling or crippling. This weakening and deformation caused a few floors to fall, while the weight of the stories above them crushed the floors below, initiating a domino collapse."

Full article is here:

http://www.tms.org/pubs/journals/JOM/0112/Eagar/Eagar-0112.html

I have another one as well I'm still reading I'll post in a minute.

This MIT professor claims tempertures reached 1500 F, and also concurs with the steel buckling theory:

http://web.mit.edu/newsoffice/2001/skyscrapers.html

I was just about to comment when I read your post that the Botanist is way too smart for me, especially after a couple of drinks. Kinda reminds me of my Dad.

Should we capitalize BOTNST from now on? :)

Ok, here's the MIT motherlode at this link:

http://web.mit.edu/civenv/wtc/

It provides in-depth reports on all aspects, and offers a compliation of articles published from Sept 2001 thru Feb 2002. It has a great deal of technical information.

Oh I'm sure people here could shoot holes all over MIT's theory:rolleyes: , what to those eggheads know about biodiesel? :confused:

Thanks Kirk. That's a show-stopper for conspiracies. I read the summary and that's good enough for me.

Conspiracy theorists must jump that hurdle before I pay attention to them in the future.

It is possible that these buildings imploded the way they seemed to without engineered assistance. We see documentaries on TV that make it sound like it is an engineering miracle when much smaller buildings are brought down so cleanly. It does give rise to suspicions. It appears that either those demolition companies are a scam or these buildings had help coming down so cleanly or maybe it was a miracle, amen.

People tend to look for complex conspiracy theories in events like this because the simplicity of what really happens seems so impossible to us - in order to do something so cataclysmic - it must have taken more than Tim McVeigh and a Uhaul full of fertilizer and a couple of crackpot friends, or John Wilkes Booth and a couple of crackpot friends, or Lee Harvy Oswald and a 19$ rifle, or 19 sucidal fanatics in an airliner. To quote Bertrand Russell, things are pretty much as they seem to be. A suicide squad flew an airliner into the building. The building was not designed for that particular event. The design shortcomings resulted in the collapse of the building due to a catastrophic fire. End of story.

Personally, I think the idea the WTC could be secretly wired for demolition is preposterous. The risks involved of commiting mass murder for insurance money, the size of the conspiracy required where all who participate must remain quiet, the fact that the building maintenance and security personnel would have to be part of the conspiracy, all make this idea speculative hogwash to me.

Go follow the link that Kirk provided and read the summary. If the summary doesn't convince you, go read the PDF's. When you (or anybody) can refute that stuff, I'll join the conspiracy mongers. Until then, case closed.

I saw an article originating from NOVA that says the combined effects of temperature difference and the points where the floor trusses interface with the side supports are thought to be the lead causes for the structural failure. http://www.pbs.org/wgbh/nova/wtc/collapse.html

Thinking about Botnst’s comment, and not pretending I can do the math, wouldn’t the earthquake dampening elements of the structure’s foundation stop or greatly dampen any P waves moving through the structure, as they are built to withstand the entire mass of the building plus foreseeable shocks originating from earthquakes.

If you read the MIT studies, they cover the temperature differentials and cite it as a key factor. As I mentioned early, the key event was that some upright member of the core structure merely need to bend a little - melting of the steel was not required - to begin the cataclysmic chain of events. I saw elsewhere on the MIT site that that NOVA program was based on these studies.

I didn't know about the earthquake dampening devices. I assume that they are for dealing with transverse (S) waves or L waves (Rayliegh) not compression waves (P). But I sure as heck don't live in an earthquake area, so I have never looked into earthquake dampening. I'd be real curious to see how somebody would design a massive vertical structure capable of withstanding or dampening thrust from any direction. Got a link?

Hmmm. But thinking about it, I guess that the dampeners would probably be most concerned about lateral thrust, to prevent development of a "Tacoma Narrows Bridge" type harmonic oscillation. I guess you'd have a footing that would allow X or Y movement but no Zed. The building is undoubtedly strongest in the vertical.

In the Northeast, there are no specific requirments for earthquake contingencies other than the "moment welds" - superstrong heliarc welds strategically placed to hold the building together during an earthquake. The guys who make these welds are the highest paid ironworkers. In California, large buildings are built on enormous coil springs and shock absorbers, not much different from that found on '57 Chevy.

I haven't downloaded the MIT PDF's because my home connection is too slow, but I don't see any reference in the summary to Bldg 7. That's the point at which most critics see the crucial questions, even though they don't think there's evidence for enough heat in the towers to cause them to fail. Bldg 7 had no structural damage and no jet fuel, yet a 43 story building is completely destroyed. Unheard of.

Each building weighed an estimated 500,000 tons each, excluding contents. If one was to stick with the most obvious as being the most likely, since the evidence suggests Bldg 7 came down of its own accord, my guess is BLDG 7 sustained initial shock damage to its foundation, and then when the second tower came down, the building collapsed from the second round of shock waves after being weakened by the first. Perhaps I misunderstood Botsnst before, and this was what he was actually saying. I could not see harmonics and shock waves bringing down the WTC from the plane impact, but it certainly makes the most sense in relation to a 43 story building directly adjacent. In fact, if we remove magical theories of demolition bombers and such, it is the only theory that makes any sense.Put a stack of poker chips on a board, drop a rock two feet away on the board - what happens? Restack the chips. Move one foot closer. Do more poker chips fall off the stack? Move one inch to the stack - you get the idea.

On one of the MIT web pages, it mentioned an exhaustive study of the entire event from an engineering perspective available from MIT Press:

http://web.mit.edu/newsoffice/2003/wtc.html

I am sure it would cover the adjacent buildings in detail.

Yeah, I'm still wondering about that one, also.

Keep in mind that the energy created by the falling towers is not going to be absorbed by soft earth - it is going to go directly into the same bedrock that the adjacent buildings has it pilings sunk into - 500,000 lbs of mass transferred almost instanteously directly to bedrock- twice - the majority of energy is not going to be transferred over the ground - it is going to shoot up into that building via rock and iron. That building must have hummed like a bass guitar string plucked with a 5 iron. Remember all those pins I mentioned holding together the columns at splice points? They must have snapped like tootpicks from sheer forces as the building moved up and down with the shock waves transmitted thru its pilings.

In addition, one must take into consideration how the pilings connect to the building itself. Long runs of angle iron are driven with a pile driver deep into the rock at the points where the core columns are located. Then a concrete form is built around the protruding angle iron, concrete is poured and enormous anchor bolts are sunk into the wet concrete. The base columns are then bolted to these anchors after the concrete has cured. A few of these sheering off would give you the exact same effect one gets from an implosive dynamite charge - in fact they pack these charges at exactly those points. The most instructive piece of info would be an examination of those column bases and anchor bolts.

Bldg 7 came down about 7 hours after the towers. There was no visible evidence of damage from the towers falling and the owner, Silverstein, said just before it came down, "Let's pull it."

I cannot have it both ways, can I? If I look at all the reasons people have proposed for bringing down the Two Towers and feel confident that there is only one reasonable cause, why can't I do that for #7?

Is there an engineering analysis of #7's failure?

What is the official name of the building?

WTC 7 I think.

I believe NIST did an engineering analysis. The hypothesis was similar to the towers. Fire from diesel fuel stored in the building for emergency generators weakened the steel and caused the collapse. I believe I paraphrase their conclusion correctly "Our hypothesis has a very low probability of occurence."

If I find the link to that study, I'll post it.

This is another one of the points that leads to doubts. There are supposedly seismographic recordings of the buildings as they fall. The peak disturbances are not from when the buildings hit the ground but from when they begin to freefall.