Why The WTC Buildings Collapsed: Two Engineering Articles

[Bolo Boffin]

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

It is known that structural steel begins to soften around 425°C and loses about half of its strength at 650°C.4 This is why steel is stress relieved in this temperature range. But even a 50% loss of strength is still insufficient, by itself, to explain the WTC collapse. It was noted above that the wind load controlled the design allowables. The WTC, on this low-wind day, was likely not stressed more than a third of the design allowable, which is roughly one-fifth of the yield strength of the steel. Even with its strength halved, the steel could still support two to three times the stresses imposed by a 650°C fire.

The additional problem was distortion of the steel in the fire. The temperature of the fire was not uniform everywhere, and the temperature on the outside of the box columns was clearly lower than on the side facing the fire. The temperature along the 18 m long joists was certainly not uniform. Given the thermal expansion of steel, a 150°C temperature difference from one location to another will produce yield-level residual stresses. This produced distortions in the slender structural steel, which resulted in buckling failures. Thus, the failure of the steel was due to two factors: loss of strength due to the temperature of the fire, and loss of structural integrity due to distortion of the steel from the non-uniform temperatures in the fire.

The fireproofing was knocked off in places and left on in others. Fire affected the two areas quite differently, with 150°C temperature difference easily obtained between the two areas. The fire burned hard in some areas and wasn't present in others, another source of non-uniform temperatures that were affecting the structural steel.

Also:

www.gostructural.com/V3N7/WTC.pdf

It's a great .pdf, chock full of good information. The words "modulus of elasticity" are used. The words "controlled demolition" are not.

The NIST site is always worth checking out as well:

http://wtc.nist.gov

[Bolo Boffin]

1. What kind of force did the upper floors hit the lower floors with?

When the floors above the impact zone fell one story, they hit the next floor with 30 times the force they had exerted on the floor in the undamaged structure.

http://www.scifidimensions.com/Oct01/wtccollapse.htm

Download the .pdf file - it's a series of 9 slides.

Slide 8 estimates the impact forces using the equation found on slide 7.

30 times the force! And this was against structural steel that had been suffering its own stresses due to a non-uniform fire...

No demolition charges necessary.

[Old and In the Way]

2. The floors were something like 2' thick concrete, right?

If so, they make a hell of an insulating oven for everything in between, I'd think.

[OudeVanDagen]

3. four (4) inch thick

[plaguepuppy]

20. Sci Fi Dimensions?

Is that a peer-reviewed journal?

[Bolo Boffin]

22. Is your website peer-reviewed?

By actual engineers?

[Name removed]

23. Deleted message

Message removed by moderator. Click here to review the message board rules.

[Bolo Boffin]

27. The slide presentation didn't originate with SciFi Dimensions

From the website:

Thomas J. Mackin, Associate Professor in the Department of Mechanical Engineering at the University of Illinois, has created an 8-slide presentation to explain exactly how and why the WTC collapsed.  ...Dr. Mackin created this analysis at the request of his school's administration, as part of an overall effort to help students and faculty discuss and understand the tragic events of September 11.  One of his students emailed the presentation to some friends, and pretty soon it was carried all over the world.  When we received it, we contacted Dr. Mackin and obtained his permission to post it on scifidimensions.  

The slideshow we have posted is actually a corrected version from the one that has spread out across the globe.  Dr. Mackin freely admits: "In my haste and in my depression I made a typo which turned into a numerical error.  It does not affect the conclusion, but it does have an effect on the numbers."  He also expressed amazement at how far and wide his work has traveled.  "I had no idea that my simple presentation was going to make its way around the world!... Regardless, this WEB is an interesting story as well...how a simple lecture for my class ended up being e-mailed by a student, then shipped round the world, and generated a huge amount of incredibly stimulating interaction."

[demodewd]

55. The South Tower

http://www.libertyforum.org/showflat.php?Cat=&Board=news_international&Number=356126&vc=1&t=-1 The evidence showing that the World Trade Center towers were demolished is compelling. Here are a few photos of explosives detonating during the collapse of the South Tower. Each frame is numbered by its position in the video. The video was shot at 30 frames per second. So an eight frame interval covers about one quarter of a second.

Frame 147 shows a row of explosives detonating right across the east face at the 79th floor.
Frame 203 shows a row of explosives detonating right across the east face at the 75th floor.

The right photos show the dust from the explosions outlined in red.

The third row the photos show the relative positions of the two lines of dust.

It has been claimed that the explosions of dust that span the east face of the tower, were caused by air being forced from the windows as each of the floors above collapsed. This explanation is obviously incorrect. If it was correct, such lines of dust would have been expelled from the windows of each floor in succession. That is, we would have seen such lines of dust expelled from floors 79, 78, 77, 76 and 75 in succession, but what we observe is an explosion of dust at floor 79, no new clouds of dust for a few floors, then another explosion of dust at floor 75. It is worth noting that the second line of (much larger) explosions occur at the center of a section of mechanical floors (the three mechanical floors appear as a slightly darker gray band across the building and are important for the strength they impart to the building). It is possible that the mechanical floors 76 and 75 (and also 74) have no windows, but of course, if this is so, it raises many more questions than it answers. In particular, if the mechanical floors have no windows, then the explosions of dust from floor 75 cannot be caused by air being forced from them as the floors above collapsed.

The dust due to the visible explosions is a whitish grey. The dust from the demolition of the upper section (which is disintegrating as it falls) is dark grey. One wonders what caused this difference.

A sequence of still photos of the collapse (at quarter second intervals) is included in http://www.nerdcities.com/guardian/WTC/south-tower.htm.

In these frames, we can see that the top 35 or so floors have snapped off and are toppling eastward. In the above frames we follow the north-east corner of the tower as this 35 floor section collapses. Using the north-east corner as a reference I have outlined in red the progress of this 35 floor top section as it descends.

The first thing to note is that the top section itself must be disintegrating otherwise (as the above frames show) the top section would have extended far into parts of the building that are clearly as yet unaffected by the collapse.

But what could possibly cause the top section to disintegrate? And in fact, what could possibly cause the top section to almost entirely disintegrate, before the lower section begins to collapse?

You have to realize that most of the top section had not been affected by the aircraft strike or fires and was thus still the same immensely strong structure that had supported the building for more than 30 years. If this section was going to fall at all, this section would fall as one piece (like a tree in the forest). Unless, of course, this section had been laced with explosives and was undergoing a controlled demolition of its own, just a few moments before the lower part of the building was demolished.

[demodewd]

56. dust segregation

"The dust due to the visible explosions is a whitish grey. The dust from the demolition of the upper section (which is disintegrating as it falls) is dark grey. One wonders what caused this difference." Notice that the two different colorations remain separated. They never mingle. This proves that the upper section is not crashing into the lower section.

[OudeVanDagen]

57. deja vu .... all over again

"But what could possibly cause the top section to disintegrate?"

One word ... motion. Any structure that can not dampen motion will collapse.


"It has been claimed that the explosions of dust that span the east face of the tower, were caused by air being forced from the windows as each of the floors above collapsed. This explanation is obviously incorrect. If it was correct, such lines of dust would have been expelled from the windows of each floor in succession. That is, we would have seen such lines of dust expelled from floors 79, 78, 77, 76 and 75 in succession, but what we observe is an explosion of dust at floor 79, no new clouds of dust for a few floors, then another explosion of dust at floor 75."

"Air being forced ..." blah blah blah, well that's actually just one small part of the much larger explanation. From the videos and still photography posted ... by you ... it's clear that collapse speed and collapse uniformity were not constant. The only possible way you could be able to observe floor by floor in succession 79 - 78- 77 - 76 collapse venting is with "controlled demolition" where collapse speed and uniformity is well planned and under absolute control.

BTW; Why do you choose to just focus and limit your observations and restrict your theory to just one or two exterior faces ... isn't anything happening on the other exterior sides ... and what about inwardly?


"You have to realize that most of the top section had not been affected by the aircraft strike or fires and was thus still the same immensely strong structure that had supported the building for more than 30 years. If this section was going to fall at all, this section would fall as one piece (like a tree in the forest)."

WTC was comprised of two tubes ... an inner core and outer wall ... and these two elements were joined and interconnected with roof trusses. All three elements; 1) the inner core, 2) the outer wall, and 3) the roof truss system (ROOF TRUSS ... NOT floor trusses) repeat ALL THREE ELEMENTS had to be intact to dampen motion and prevent collapse. That 'top section' was not 'immensely strong' ... it had drifted (remember drift?) from the lower section and the three building elements were no longer intact and interconnected and no longer capable of controlling motion.

That upper section could never fall as; quote: "one piece (like a tree in the forest)" end quote, because: 1) it did not have the rigidity of a typical steel framed structure (remember ... two tubes and suspended floor trusses ... NO typical structurally redundant steel framing) and 2) that section was 200X200 and several thousand tons ... weight wins.


deja vu all over again ...



Five (5) quickie questions:

1)Where is the residue from all your explosions?
2)How many columns and beams and collateral framing members displayed explosive damage; tear-out, delamination, and so on?
3) How many WTC collapse reports have you read .... that you can link us to?
4) How many structural collapse investigations have you participated in?
5) How many non 911 WTC collapse reports have you read?


One fast answer to all five (5) questions: NONE

[demodewd]

58. Where's the hammer??

Fine. "Drift"...who's arguing? But its obviously not falling into the lower section. Its artificially suspended by the rapid charges. Otherwise the the coloration of the lower section plumes would take on an admixure of the upper floors smoke and the lower floors cement et al plumes. There's no hammer,its been interupted, momentarily.Weight wins...unless nature is treacherously interrupted..as in this case. It would not just be collapsing...it would be falling.

[OudeVanDagen]

59. artificially suspended ... okaaaay

"...its obviously not falling into the lower section. Its artificially suspended ..."

Artificially suspended is a very interesting concept that you're offering up there, demodewd .... pretty good, its right up there with some of your other concepts: acid rain, mystery concrete, deteriorating aluminum, building obsolescence; and of course the still airworthy planes, the still living dead with SSNs, and those "gassed" airliner passengers.



"Where's the hammer??" you ask ... well, I don't know. BUT since you're a big music lover and have generously offered these forums some lyrics and tunes I'll offer up a taste of my favorite Hammer song:

"My, my, my music hits me so hard
Makes me say "Oh my Lord"
Thank you for blessing me
With a mind to rhyme and two hype feet
It feels good, when you know you're down
A super dope homeboy from the Oaktown
And I'm known as such
And this is a beat, uh, you can't touch

I told you homeboy (You can't touch this)
Yeah, that's how we living and you know (You can't touch this)
Look at my eyes, man (You can't touch this)
Yo, let me bust the funky lyrics (You can't touch this)"

[demodewd]

60. hooey

I mentioned gassed passengers...the rest is all hooey. You're not addressing my points. So go away.

[TrogL]

61. Your own photographs disprove it

Look at the top photo. The tower has already started to lean before the "explosion" that apparently takes out the windows.

Those aren't explosions. Those are sets of windows breaking - releasing pent up smoke. The windows don't break on every floor because there isn't sufficient pressure to break the windows.

[demodewd]

62. get serious

Whaaaaat??

[Bolo Boffin]

63. Interesting reaction...

...it's one I'm quite familiar with.

[OudeVanDagen]

64. hey fellas ....

Those squibs and puffs aren't explosions from subversive devices. What demodewd calls evidence for explosions and controlled demolition is ... for the umpteenth time by the way ... a collapse sequence called "venting" ... an accepted term ... sometimes also called blow-out.

Venting is a visual sequence that occurs early in the collapse incident. It disappears if collapse speed rapidly increases.

Venting follows the leading edge of collapse ... a knife of sorts well below ... several floors below(*) the dispersal or scattering of debris in the collapse scenario being discussed. The leading edge can not be seen as it is masked by exterior walls. A brick structure would display cracks, a curtain wall or glass and aluminum skin that expands and contracts with thermal loads and allows wind movement doesn't reveal what's happening behind it when that leading edge passes through.

(*) footnote: venting in the old oft-repeated photos being offered up by demodewd is seen below the dispersal ... it can also be above; but collapse speed - how fast the event happens will allow or disallow clear visuals of venting.

The leading edge is the extreme compressive and tensile forces acting on the columns, beams, and collateral framing members. Extreme meaning that the forces exceed the yield and shear strengths in the MOE or Modulus Of Elasticity for the steel. These destructive forces are created by motion. In the WTC 911 events there was extreme motion. AS already stated, the three (3)elements for WTC were the 1) outer wall, 2) core columns) and 3) roof trusses. All three (3) had to remain intact and connected for the structure to dampen motion. The photos offered show that these three (3) elements were disassociated and could not dampen motion.

Venting follows the leading edge. As the columns, beams, and collateral framing members fail ... drift ... bend, etc etc floors, concrete, insulation etc etc disassociates and forces energies out through the fenestrations and inward to the service shafts.

Venting ... it's color means nothing, it's the distance traveled and speed of venting from the building that matters. (But not to all collapse experts ... we don't all always agree). That info is achieved with carefully measured investigations of video by experts who measure speeds for rocketry and other propelled weapons.

Venting has been recorded in numerous structural collapse worldwide. It's very clear in WTC 911 video, and to the untrained eye of a devout controlled demo proponent it looks like explosives, but to those who deal with the hundreds of structural collapse incidents worldwide it's commonplace .... it happened and was caught on video in the very recent collapse incidents in Turkey, Taipei, and in Egypt.

Venting is normal. It's just one part ... one of many sequences to collapse ... ALL of which are initiated by the structure's inability to dampen motion. A structure that can not stop motion and regain stability will collapse.

So where's the explosive residue? Engineering students and bomb investigators in training can find bomb and explosive residue from WW2 in London, Berlin, and Dresden; and now find it all over Basra. Where's the NYC stuff? There had to be TONS of it to ""artificially suspend"" a couple thousand tons of WTC's upper section ... TONS! So where is it??

[RossMcLochNess]

4. Its strange...

where are all of the conspiracy theorists today? Yesterday they wanted engineering proof because according to many, the towers couldn't have collapsed via the airplanes. Now today someone has posted some links but they all seem to be busy ;-) Thanks for the links, they were interesting reads.

[Bolo Boffin]

5. Not so strange...

The reader can judge who's really trying to understand what happened that day: the experts in charge of building better buildings tomorrow, or people online with a bunch of pictures and a Paypal button.

[medienanalyse]

6. Bolo, I was rude to you some days ago

and I still stand firm to that. You had just stated that you know who is who on photos, and that you know when they were made. That was the metabolized result of a meal of a male cow.

But these two articles are good and substantial. Thank you.

[Bolo Boffin]

7. I respect "rude".

It's part of the political conjugation of Opinionated:

I am a Opinionated Smart *ss, You are Rude, He/She is a $%#*!#@ B*stard!

About the woman in the picture, I've admitted I was wrong about that. I still don't know what the woman in the picture is supposed to prove, but she's there.

But I've been here for two years now, and I've dealt with many a metabolized result of a meal of a male cow. It's quite frustrating to see the same old arguments used which have been debunked time and time again. When I get out of line, I expect to be corrected.

Because in the end, it's not about whether I'm right or wrong, it's about the truth.

[Abe Linkman]

8. Right about that.

"Because in the end, it's not about whether I'm right or wrong, it's about the truth."

And the truth is NOT the Official Story, and what DID happen wasn't the result of mere negligence or criminal negligence or intelligence failures. 9-11 was an inside job. FL 77 didn't crash into the Pentagon, or anywhere else. Ted Olson's claims about his wife's cell phone calls are a lie. A "necessary" lie on the part of the Gov't, in order to establish crucial "facts" to frame the Cave people and fool the American people.

Osama was working with the CIA. Otherwise, why would the local CIA station chief have met with him when he was having his radiators flushed, in July 2001? The CIA knew he was in a military hospital in Pakistan on September 10, 2001. CBS reported it. Did the CIA visit him then? If so, why? The Pakistani ISI Head was in Washington at the same time. It's impossible to believe that the US Gov't didn't know where Osama was. This wasn't negligence or a failure of all US AND Pakistani Intelligence.

Why anyone who has a modicum of knowledge about 9-11 would continue to insist on the fantasical "Wacky Cave People Did It" Conspiracy Theory,
is beyond me. Are they being negligent? Is it a failure of cranial intelligence? What?

[plaguepuppy]

15. the experts in charge of building better buildings tomorrow

Gosh, my heart swells with hope at the sound of that! Where do I sign up for the Better Tomorrow?

[Bolo Boffin]

17. John Kerry's website

http://www.johnkerry.com/

Now do you have anything of substance to add to this discussion?

[plaguepuppy]

16. Had the daY OFF !!!

You should check out the real world (AKA 3-space) some time - not all the good stuff is mediated by a keyboard.

It's stunning how easily you guys lapse into spasms or self-congratulation...

[Bolo Boffin]

18. Would you mind reading the articles...

...and commenting on them instead of posters?

[plaguepuppy]

24. Read them a long time ago, thanks

...see comments elsewhere in the thread

[NecessaryOnslaught]

9. Briefly, in your own words..

"As the joists on one or two of the most heavily burned floors gave way and the outer box columns began to bow outward, the floors above them also fell. The floor below (with its 1,300 t design capacity) could not support the roughly 45,000 t of ten floors (or more) above crashing down on these angle clips. This started the domino effect that caused the buildings to collapse within ten seconds, hitting bottom with an estimated speed of 200 km per hour." http://www.tms.org/pubs/journals/JOM/0112/Eagar/Eagar-0112.html

If the floors were "pancaking", and the angle clips, connecting the trusses to the perimeter and core columns, failed, then WTF pulled the core down??


or was it that the central core, not the trusses, failed first?


"The report exonerates the floor trusses for the collapses. "Failure of the floors...was shown not to have had any significant role in the initiation of the collapses," it says. Studies by Hughes Associates and ARUPFire led the team to conclude that tower floors survived the initial impact of the planes, suffering only localized damage. On the basis of a review of smoke plumes and fire spread, for each tower, the engineers concluded that the fires did not lead to the collapses of the floors affected before the towers fell. Additionally, the engineers claim that computer modeling shows that the failure of columns alone, independent of the floors explains the collapses.
....concludes the report's authors, a team of engineers from several firms working for Silverstein Properties Inc., the New York City-based leaseholder of the World Trade Center."



http://enr.construction.com/news/buildings/archives/021025.asp

[Bolo Boffin]

12. Very good...

As you can see, there are several hypotheses for why the towers fell, and good information behind each. They actually work well with each other.

What I gather the Silverstein-sponsored report to claim is that the floor trusses or angle joints aren't responsible for collapse initiation. The column failures, due to the damage done by uneven heating combined with higher load levels, is what the Silverstein report says.

This gets the top section falling. That's where the pancaking takes over. As the slide .pdf shows, the force of the falling section was 30 times the force of simply supporting the section in an undamaged structure after falling the distance of a single floor. These forces snap the floor below, adding its mass to the momentum downward.

Brief enough?

[OudeVanDagen]

14. Hired guns

"Silverstein-sponsored " is a key phrase to properly assess Weidlinger ... as is the report date ... summer 2002, and the process ... based on FEMA data. Hard pills to swallow ... IMHO

"there are several hypotheses for why the towers fell"... TRUE

"good information behind each"... EXCELLENT

My two cent advice is to study ALL the reports, in full ... appendums and footnotes. Make your own assessment ... but things to remember; a) report dates ... how soon after the collapse incident was the preliminary or final report filed .... and which one are you reading, b) who paid for the report ... is the report by an independent or by a hired gun, c) where did the team obtain their data ... was it from FEMA, the collapse information pool or is it from their own legwork, d) summaries are simple overviews ... the meat you wanna sink your teeth into is buried somewhere in the report, and e) newspaper coverage is generally poor ... too much or too little out of context excerpting can send false message, and you're reading one reporter's understanding of technical terms.

Signs of a well researched, independent and unexpedited report; a) multiple scenarios offered and clear process of elimination, b) detailed appendums, footnotes and credited photographs of self-collected data, c) inclusion of opposing views and contradicting evidence, and d) preamble or disclosure statement of funding.

As always .... study other collapse incidents too. It's time well spent to learn about structural elements and connections, collapse terms and the investigation process.

It takes time, energy and a lot of reading to understand WTC ...

[NecessaryOnslaught]

10. One more minor question..

??

[Bolo Boffin]

11. You didn't read the GoStructural .pdf

or your minor question would have been answered.

More information here:

http://www.fema.gov/library/wtcstudy.shtm

[plaguepuppy]

21. Excuse me?

That's like saying "see the encyclopedia for the obvious answer." The Building-7 collapse is explained by the FEMA report? That comes as a surprise to those of us who have actually read it!

And about that "GoStructural" article that you count so valuable, it's an article from a "throw-away journal" called Structural Engineer (http://www.gostructural.com/) from August of 2002. This type of journal exists in most professions, and will be sent to you for free whether you want it or not. The article in question is nothing more that a brief summary of the FEMA report, which itself makes no claims to actually explain how the collapses took place. The authors of the FEMA/ASCE document take great pains to delineate the scope of their study, which is only preliminary and does not attempt to "prove" any particular scenario. To claim that a popularized article in a non-technical journal can come to conclusions more definite than the "Building Performance Study" it is based on is simply ridiculous.

[Bolo Boffin]

28. Why do you always overstate the case, plaguepuppy?

To claim that a popularized article in a non-technical journal can come to conclusions more definite than the "Building Performance Study" it is based on is simply ridiculous.

Where did I ever claim such a thing?

The GoStructural article is a simple summation of the FEMA report? Fine. I'll take your word for that.

Since NecessaryOnslaught's "question" consisted entirely of a picture of WTC 7, I assumed that the question was what about this collapse. I knew that the WTC 7 collapse had been treated in the GoStructural article, so I directed NO to it. Then you come along, claiming that I said the GS article was the last word on the WTC 7 collapse?

I'd appreciate if you'd deal with my actual words, instead of the words you put in my mouth.

[TrogL]

13. Excellent work

Thanks for posting it.

[plaguepuppy]

19. This is all old stuff, and answers nothing

The Eagar article is little more than conjecture when it comes to speculating on the actual collapse sequence, and offers no quantitative analysis to support its conclusions. The most interesting point he makes is that the fire was not as hot as was widely believed:

"Diffuse flames generate the lowest heat intensities of the three flame types.
If the fuel and the oxidant start at ambient temperature, a maximum flame temperature can be defined. For carbon burning in pure oxygen, the maximum is 3,200°C; for hydrogen it is 2,750°C. Thus, for virtually any hydrocarbons, the maximum flame temperature, starting at ambient temperature and using pure oxygen, is approximately 3,000°C. This maximum flame temperature is reduced by two-thirds if air is used rather than pure oxygen."

But when it comes to explaining the initiation of the collapse he simply asserts: "As the joists on one or two of the most heavily burned floors gave way and the outer box columns began to bow outward, the floors above them also fell."

This means that despite the fact that the fire wasn't hot enough to seriously soften the steel throughout most of the structure, and despite the fact that the fire would have long since exhausted its fuel in the area closest to the initial impact, it is in this area that the floors are supposed to have suddenly given way. For the floors to drop straight down as he describes the floor supports whould not only have to fail, but to fail equally and simultaneously around the perimeter of the floor. If, as is more plausible, one side failed first, the floor would tilt and "jam on the spindle" like a balky record rather than initiating a nice symmetrical collapse.

And where exactly can we see this "bowing outward" of the perimeter columns that is supposed to have occurred?

[Abe Linkman]

25. Arguing causation is tough to do w/someone who isn't neutral

It only allows non-truth seekers the opportunity to continue the cover-up.

Doesn't it strike you as a little bit odd that some of these people seemingly have expertise in a whole lot of disciplines? They must be geniuses. Oh, wait. I know what they can say about THAT: they're just very interested and concerned, don't pretend to be experts, just your everyday sort of person with a little more than a casual interest in 9-11 events and so they've brushed up on a lot of subjects...you know, like a good trial lawyer makes him/herself knowledgeable about subjects they knew nothing or little about, prior to getting involved in a particular case.

You can't win in a "he said, she said" game where the rules forbid bringing up possible motives.

[Bolo Boffin]

26. You're not dealing with all of Eager's factors.

This means that despite the fact that the fire wasn't hot enough to seriously soften the steel throughout most of the structure, and despite the fact that the fire would have long since exhausted its fuel in the area closest to the initial impact, it is in this area that the floors are supposed to have suddenly given way.

What about the columns that were severed when the plane impacted?

wtc.nist.gov/images/WTC-007_hires.jpg

What about the non-uniform temperatures? As Eager points out, even a difference of 150 degrees is enough to induce "yield-level residual stresses. This produced distortions in the slender structural steel, which resulted in buckling failures."

What we have is the fireproofing being knocked off of sections of the structural steel and the exposed areas being heated disproportionately to the unexposed steel. The columns in the damaged, fire ravaged floors finally buckle and fail. And as the slide .pdf points out with the top section only had to fall the distance of one floor to achieve 30 times the force of simply supporting the weight of the section in an undamaged structure.

he floor would tilt and "jam on the spindle" like a balky record rather than initiating a nice symmetrical collapse.

Who anywhere besides you claims a "nice symmetrical collapse" for the non-controlled-demolition explanation? This is your straw man, plaguepuppy, which you paste onto this explanation.

The South Tower explanation takes into account that the corner failed first. The collapse didn't jam on the spindle - the resulting forces of the moving top section ground the "spindle" into dust and continued its way down.

I don't have pictures of the "bowing out." It doesn't mean it didn't happen.

[NecessaryOnslaught]

29. whats it gonna be?

You're flip-floppin. Two days ago you were doin the pancake, and now you're doin the hammer of the gods. Are you saying that this free-floating cube of 20-30 floors (closer to 30 in the south tower, closer to 20 in the north), which was created when the core was blasted( oops, im mean the core columns "buckled"), proceeded to mash the rest of the building to dust all the way to the ground? Including the cube itself? Or do we have a new hybrid theory unveiled right here at DU, the hammer-pancake? :nopity:

[LARED]

30. free-floating cube ????

Cubes have 6 sides. Like dice. Even if dice are hollow, you can roll them around and they manage to stay in one piece. The "cubes" of the WTC were not nine sided. You can't roll them, turn them over, or spin them and expect them to remain in one piece.

Also, let me ask you something. Lets assume for a moment that the south tower was indeed "blasted" to create this cube. You seem to be trying to make the argument that even if this was true the so called cube would have just fell over and left the towers standing below the cube's blasted area.

Is that your argument? If so, please explain how the structure would manage to accomplish this feat. Sounds like you are trying to suspend the laws of physics.

Edit to change 9 sides to six sides (Duh)

[Bolo Boffin]

31. My take on how the towers fell...

...is open to the facts.

This is nothing new. Saying that the floors pancaked down assumes a force pressing the floors together. That force was the top section of both buildings after the last of the core columns buckled. No flip-flop.

Are you saying that this free-floating cube of 20-30 floors (closer to 30 in the south tower, closer to 20 in the north), which was created when the core was blasted( oops, im mean the core columns "buckled"), proceeded to mash the rest of the building to dust all the way to the ground?

Words like "free-floating" and "blasted" aren't from me - they're your pejoritive take of what I'm saying. "mash the rest of the building to dust": Not entirely, but that's where the slurry came from.

Including the cube?

The top sections broke apart into pieces, not dust, when they had no farther to fall.

Or do we have a new hybrid theory unveiled right here at DU, the hammer-pancake?

Nope, nothing new. The same theory that scientists and engineers have been working on for quite some time. Perhaps it's new to you - you should examine where you've been getting your information from.

[plaguepuppy]

49. Eager's factors

"What about the columns that were severed when the plane impacted?"

Not a significant factor - the damage to the South Tower core went obliquely through the SE corner, and doesn't seem to have taken out much of the core. Judging from the fact that almost no debris exited through the east wall (a big fireball but no visible fragments, and only a small hole near the SE corner) with its 14" square box columns, we would not expect major damage to the larger core columns.

And initial damage to some of the core columns contributes nothing to weakening the remaining ones. The fact remains that there is very little fuel within the core itself, and the areas nearest the initial crashes would have long since burned out. Air for the fires came almost exclusively from around the periphery of the building, which places the hottest part of the fire as far as possible from the core. Despite claims that the core acted as a chimney, architects who worked on the project (e.g. Aaron Swirsky) say that there were built-in fire shutters that were designed precisely to prevent that from happening. Swirsky even expressed concern that this "hermetically sealed" design of the floors might have interfered with evacuation.

"I don't have pictures of the "bowing out."

No, you certainly don't, and neither does anyone else, despite the hundreds of still and video cameras that caught the collapses from their very first moments. Most rational people would take that as pretty strong evidence that it didn't happen, but of course I would not expect you to be so easily dissuaded.

As for your "a little of this, a little of that" collapse model, you still lack a plausible mechanism for causing all the core columns to fail at once, either at the level of the crashes or throughout their entire lengths as we see in the actual collapses. With or without fireproofing the columns act as powerful heat sinks, and cannot be heated to the softening point without a much greater energy input than the fires can provide.

[DeadBroke]

51. I'm having problems ....

... plaguepuppy, with your assessment that "initial damage to some of the core columns contributes nothing to weakening the remaining ones" because, as you know from my past efforts to relate some of my ironworking experiences (and hopefully remembering my cooperative respectful approach), only the opposite is true.

Losing a couple of core columns may not seem significant, but it is; because each and every column is connected to the one above and to the one below. Each column is also connected to at least 3 to 4 beams at top and to at least 3 to 4 beams at bottom - which in turn are connected to other columns. Each and every column also has chevrons or cross bracings that are connected to other columns and/or beams. All these numerous connections are made with several high grade bolts tightened to specified torques and these connections are also welded; almost always during that era with welding electrodes in the 60 to 70 thousand pound range.

Whatever happens to one column always affects those to which it is attached.

During the erection each column is plumbed and racked. Cables are placed between columns to form an X and turnbuckles are twisted until the columns are perfectly plumb and racked. (1/16" off was always tolerable, no longer). The base of a column will "stipple" from the weight of the columns and beams and other framing if it's left out of plumb or rack. Columns way out of plumb can not support the weight they are designed for and dramatically affect the columns they're attached to. It's sort of like the domino affect (please, of course I do not mean exactly like dominoes) where action on one immediately affects the one next to it.

In my ironworking experiences I have had to replace columns that were struck by busses, trucks and subway trains. In a subway derailment about 10 years ago near Union Square the train struck or came in direct contact with 9 columns, but because of the framing that connected those 9 columns to other columns a total of 17, or 8 additional had to be replaced.

And, with the same good intentions, I have to disagree with your view that "Judging from the fact that almost no debris exited through the east wall (a big fireball but no visible fragments, and only a small hole near the SE corner) with its 14" square box columns, we would not expect major damage to the larger core columns." I disagree because IMHO that lack of exiting debris suggests to me that the core columns caught the debris - and also caught the forces of their impact.

In all honesty I haven't a clue as to what strengths those forces were or how to measure or estimate them, but I believe the impact caught by those core columns was significant enough to cause substantial damage to them - and, in turn, to those they were connected to.

[Bolo Boffin]

52. Damage assessment from the Silverstein report

The team determined that the initial hits destroyed 33 of 59 perimeter columns in the north face of One WTC and 29 of 59 perimeter columns in the south face of Two WTC. Computer analysis showed that the impact of the planes also destroyed or disabled some 20 of 47 columns in the center of the core of One WTC and some five of 47 columns in the southeast corner of the core of Two WTC. The crashes stripped fireproofing from columns in the path of debris created by the planes penetrating the buildings, it continues.

As the fireproof-compromised columns buckled, they compromised the columns they were connected to - the same columns that were suddenly supporting more weight because of the buckling columns around them.

And here's a simply stated explanation at HowStuffWorks.com:

http://people.howstuffworks.com/wtc7.htm

The heat expanded, twisted and buckled the steel support structure, gradually reducing the building's stability. Any number of things could have happened during this period. For example, connections between vertical columns and floor trusses probably broke, dropping sections of floor on lower levels and breaking connections between the core and the perimeter wall, possibly causing columns along the perimeter to buckle outward. Every broken connection or buckled length of steel added to the force acting on connected steel segments, until the entire structure was weakened to the point that it couldn't hold the upper section of the building.

When this happened, the top part of each building collapsed onto the lower part of the building. Essentially, this was like dropping a 20-story building on top of another building. Before the crash, this upper structure exerted a constant downward force -- its weight -- on the superstructure below. Obviously, the lower superstructure was strong enough to support this weight. But when the columns collapsed, the upper part of the building started moving -- the downward force of gravity accelerated it. The momentum of an object -- the quantity of its motion -- is equal to its mass multiplied by its velocity. So when you increase the velocity of an object with a set mass, you increase its momentum. This increases the total force that the object can exert on another object.

When the upper structure of each tower fell down, its velocity -- and therefore its momentum -- increased sharply. This greater momentum resulted in an impact force that exceeded the structural integrity of the columns immediately underneath the destroyed area. Those support columns gave way, and the whole mass fell on the floors even farther down. In this way, the force of the falling building structure broke apart the superstructure underneath, crushing the building from the top, one floor at a time.

As the Silverstein report shows, the floor trusses aren't the factor in collapse initiation that the FEMA report posited. Core column failure was enough to explain collapse initiation.

The page lists two factors for the South Tower falling first. One, the impact was lower in the South Tower, adding that much more weight to the South Tower's upper section. Two, since Flight 175 was travelling faster than Flight 11 on impact, there was greater initial damage to the South Tower, especially to the external tube structure.

No need for explosives - the airplane impacts and resulting fires explain the whole thing.

[Ameridansk]

32. I must have missed something . . .

Long, drawn-out, hypothetical theories on the "collapses" that point toward a progressive event. Theories worth a lot of money, I'm sure.

Did I miss the part where they explain why the seismic recordings of the event would look like this?



If a theory can't explain what is observed, what good is it?

[Bolo Boffin]

33. Now I'm missing something...

How does the seismic record conflict with any of the offered explanations?

[Ameridansk]

34. Subject: Well, shoot! Good Morning!

I only post at this time cuz I live on the other side of the globe. Up early for Saturday morning cartoons, or what?

I guess I just assumed that the great amount of force released when the first floors "pancaked" would also be released as the other 90+ floors (in the case of the North Tower) did the same.

Sorry, but I admit, I'm not an engineer. Can you point me to the pertinent passages that explain why the rest building went all noodley after the first "pancake"?

On edit,
I won't be back for a long while as I have a life to live away from the computer, and I know how generally worthless it is to deal with some folks on this message board. But I know LOADS of people who would be glad to read your reply. This simple problem troubles every person I know who has ever seen the seismic graph, so go get 'em, Tiger!

[Bolo Boffin]

35. If anyone can explain the seismic argument to me...

I'll be happy to address it.

You seem to be concentrating on the collapse signatures, so I'll give an interpretation of that and see if it's what you're asking for.

What we see in both collapses is a sudden buildup of noise, followed by an incredible spike of waves, which then slowly trail off.

Completely consistent with the pancaking (the buildup), the impact of the whole mess onto the ground (the spike), and then the trailoff of seismic waves as all the accumulated mess settles down.

Okay?

[DeadBroke]

36. Seismic activity ...

... was often asked about during the public information meetings NYC held about the Trade Center. For what it's worth, the engineers (Columbia Engineering) that I heard answered that the structures were not static between the impact by aircraft and final dispersal of the debris. There was movement; each of the two tubes, that is the outer wall and the inner core, had movement, swaying, twisting, whatever you call it, and that the tubes were under a great deal of weight transfer and compression and tension, all of which was at a level great enough to show up on seismic equipment in the area.

[demodewd]

37. seismic spike

How do you explain the seismic spike?

[LARED]

38. The seismic spike

I believe the reason you believe this is a spike is because in order to get a viewable signal of the impacts and the collapse data on the same chart they use a scale that makes it appear as a spike. If you or if they used a different scale for the impacts they would look like a spike as well and the collapse would be off the chart. Or if the used a bigger scale the impacts would not be seen on the charts.

Also, look at the chart on the left, it measures frequency verses displacement. To me it looks like something you may expect to see from a building collapse. You will also notice that there is no spike. Also look at the units on the right chart. It's in units of velocity. So unless you can tell me how the velocity of an explosion is going to be manifested differently that a collapse you're only persuading those that already think the seismic data is material to their fantasy.

[demodewd]

39. Nonsense.

The seismic recording at Palisades registers a profound spike at the onset of collapse which dramatically dissipates during the process of collapse. This is irrefutable.

[LARED]

40. Really?? Profound Spike????

How do you explain the small red graph inserted next to your profound spike that shows no spike? How do you explain the lack of a spike in the displacement verses frequency graph? It's all the same data -- just presented differently.

Notice the different scales used between the red and black charts.

The black is 0 to 1600 nm/sec and the red is about 0 to ~ 6000 nm/sec.

Please explain.

[Bolo Boffin]

42. Refuted.

The seismic recording at Palisades registers a profound spike at the onset of collapse which dramatically dissipates during the process of collapse.

Look at the chart again, Dewd. The spike isn't at the onset of collapse. Both events have a buildup to the spike. The spike is when the bulk of the towers hit the ground, not at the onset of collapse.

[demodewd]

44. wrong.

There is a small buildup to the spike and then a brief period of a few seconds of seismic activity while the building is still collapsing.This is obvious. You are wrong..the seismic activity has all but ceased when the bulk of the Towers has hit the ground. Seismic activity measures the disturbance below the surface not the materials falling to the surface.

[LARED]

46. Please explain

There is a small buildup to the spike and then a brief period of a few seconds of seismic activity while the building is still collapsing.This is obvious. You are wrong..the seismic activity has all but ceased when the bulk of the Towers has hit the ground. Seismic activity measures the disturbance below the surface not the materials falling to the surface.

How can you know this by looking at the data?

[Bolo Boffin]

47. Excuse me?

What is your explanation for the buildup to the spike?

Mine is that this is the seismic activity recorded as the top section smashed its way through the lower floors.

seismic activity has all but ceased when the bulk of the Towers has hit the ground. Seismic activity measures the disturbance below the surface not the materials falling to the surface.

Are you saying that the hundred of thousands of tons of material hitting the ground wouldn't have caused a recordable disturbance below the surface?

The building is connected to the ground. That's how the initial impact of the planes were recorded as seismic activity. The crash of the buildings to the ground definitely caused seismic waves.

It is you who are wrong.

[demodewd]

48. OK.

Stand corrected. The tons of steel would have recorded seismic activity below...however it would not account for the registered spike.

[LARED]

50. Can you account for the spike?

The chart has three sets of data. The velocity measurements shown in two different ways -- both showing different velocity and time scales. Then there is the third chart showing displacement verses frequency.

So, seeing as it's all the same data just displayed differently, how do you explain that the spike does not manifest itself in all three data sets?


Do you have any experience interpreting seismic data? You seem to speak as someone that knows how to interpret this data in a definitive way.

[DeadBroke]

41. Take it, leave it.

I'm not explaining anything. I'm just repeating what I heard at one of the NYC public Q & A sessions. Like my message says, "For what it's worth ... " You can take it, or leave it.

[Bolo Boffin]

43. Thanks, DeadBroke. n/t

[demodewd]

45. just curious

I was just curious if you had an opinion on the subject. :)

[rman]

53. Why The WTC Buildings Collapsed: FEMA report

Those articles come to a different conclusion then FEMA;

FEMA (Federal Emergency Management Agency)
World Trade Center Building Performance Study
WTC7
5.7 Observations and findings (page 31)
..."The specifics of the fires in WTC7 and how they caused the building to collapse remain unknown at this time. Although the total diesel fuel on the premises contained massive potential energy, the best hypothesis has only a low probability of occurrence. Further research, investigation, and analyses are needed to resolve this issue."
http://www.fema.gov/pdf/library/fema403_ch5.pdf
http://www.fema.gov/library/wtcstudy.shtm

[Bolo Boffin]

54. FEMA was a preliminary report

It laid out the issues and came to some tentative solutions.

The NIST report, due in September, will be much more complete.

http://wtc.nist.gov