My September 11 Thoughts

[XT]

Thought I’d post this since it’s one of my favorite articles From Scientific American:

When the Twin Towers Fell

When New York City’s giant World Trade Center towers plunged to earth following successive suicide terrorist attacks on September 11th, the world was confronted with one of most shocking¿and sickening¿sights of modern times. The mechanisms by which these huge and seemingly solid edifices suddenly collapsed, snuffing out the lives of thousands, was the subject of a preliminary postmortem conducted last week in Cambridge, Mass. A panel of Boston area-based civil and structural engineers convened to discuss the fate of the superskyscrapers, struck by hijacked passenger planes, in front of an overflow audience on the campus of the Massachusetts Institute of Technology. Their starkly sobering analyses highlighted the vulnerabilities of ultra-tall buildings to fire and pointed out steps that could be taken to lessen them.

“Though the twin towers were not much taller than their famous uptown predecessor, the Empire State Building, the World Trade Center rose during the late 1960s, a new era of construction characterized by rapidly erected, lightweight steel structures rather than heavy masonry walls,” explained Robert Fowler, senior engineer at the structural engineering firm of McNamara and Salvia. Fowler was then a junior member of the WTC’s engineering firm of record, Worthington, Skilling, Helle & Jackson, later renamed Skilling Helle Christiansen Robertson. “As the Trade Center was so much lighter in comparison to earlier designs, it was a watershed building in the history of skyscrapers,” he added. Leslie E. Robertson, then the project manager, was the engineer most responsible for the superskyscraper’s design, Fowler noted. He is currently principal partner at Leslie E. Robertson Associates, the current structural consultants to the WTC. The late Seattle-based architect Minoru Yamasaki designed the World Trade Center.

How the Towers Kept Standing

As with all large buildings, the main structural engineering design criteria for the facility’s 1,362-foot-tall south tower and 1,368-foot-tall north tower centered on two things: ensuring resistance to the gigantic gravity loads of the buildings themselves as well as to sideways or lateral forces caused by high winds and earthquakes, which can generate huge overturning forces at the bases. The former condition, Fowler explained, depends on specifying strong vertical columns that can efficiently transmit the mass of the building to the ground. The latter consideration concerns not only structural integrity but also “requires developing an acceptable comfort level for the occupants” by avoiding too much swaying. Opposition to lateral motion is controlled by “the design’s structural mass [weight], the stiffness of its lateral members and the degree of structural damping employed,” Fowler said.

“Though the WTC towers stood over 1,360 feet above the street level, the structures’ bases were actually set 70 feet into the ground, and one had a 100-foot-tall antenna atop it, so with 205-foot widths, they had a lot of [exterior] area facing the wind,” the engineer stated. He calculated that the approximate maximum wind shear force that a single face needed to withstand to be somewhere around 11,000,000 pounds. The gravity loads (weight) produced by the towers at their bases were on the order of 500,000 tons, Fowler said.

To handle these immense forces, the engineers “designed the World Trade Center essentially as a large beam section,” explained another panel member, Robert McNamara, president of the engineering firm McNamara and Salvia. Called structural tubes in the business, each twin tower was strongly framed in structural steel. The frame comprised inner and outer rectangular box tubes consisting of closely spaced steel box columns connected by steel spandrel members or truss beams that supported 40,000-square-foot cross-braced floors, each nearly an acre in area, the empaneled engineers said. This configuration created a complete exterior tube around the building and a center tube down the middle.

The 90-foot-long central core, formed of massive vertical steel columns that held most of the building’s weight, contained elevator shafts, stairways and utility spaces, they said. The core’s columns were thicker toward the base to support huge accumulated gravity loads. The outer perimeter tube, a tight prefabricated latticework with 61 14-inch steel box columns (spaced 39 inches on center) on each building face, provided all the bracing resistance against lateral and twisting forces from wind and seismic action. This exterior grid served as a moment frame, providing a large moment arm (of torque) against overturning and deflection forces. The outer tube bore part of the gravity-induced downward load as well as, they noted.

The huge inner and outer rectangular tubes “needed to be protected to maintain their structural integrity, so the floors acted as reinforcing diaphragms or bulkheads [the term used in shipbuilding],” said panel member Jerome Connor, professor of civil and environmental engineering at M.I.T. The office floors, which each comprised a 35- to 60-foot clear span from the core to the exterior grid, were panelized structural members supported by open web joists with steel decks above them, he said. The horizontal truss struts, bolted and welded to the exterior grid and the core column structures, included viscoelastic stringers that provided increased damping to help make the structure less lively in the wind, according to Connor. Each steel floor deck was covered with four inches of concrete. “With almost an acre of area for each floor and figuring about 100 pounds per square foot of area,” he estimated that “each floor system weighed about 3,200,000 pounds.”

And now, why they fell:

Why the Towers Fell

With all of its structural redundancies, “the World Trade Center was probably one of the more resistant tall building structures,” McNamara said, adding that “nowadays, they just don’t build them as tough as the World Trade Center.” His statement is bolstered by the fact that the support structures of both twin towers withstood the initial hits of the two kamikaze airliners despite the breaching of many levels of framing. After the deletion of key structural members from about the 90th to 96th floors on the north face of the north tower, One WTC, and from about the 75th to the 84th floors of the south, east and north faces of the south tower, Two WTC, the buildings’ skeletons found alternative paths to take the loads. Each impact and following explosion imparted first a large local lateral force and then an omnidirectional force to the structures, together causing massive initial damage to the columns and floor systems at the elevation of the crash.

Despite shocks and explosions estimated to be equivalent to that of the 1995 truck bombing of the Alfred P. Murrah Federal Building in Oklahoma City (about 400 tons of TNT), the towers remained upright. “The buildings displayed a tremendous capacity to stand there despite the damage to a major portion of the gravity system, and for an hour or so they did stand there,” McNamara said. “The lateral truss systems redistributed the load when other critical members were lost. It’s a testament to the system that they lasted so long.”

Clearly, Scientific America either doesn’t know this New Physics™, or they are in on the conspiracy, because they don’t seem to have any issue with the dreaded Official Story(arr).

The truth, of course (as most in this thread know, and those who don’t are just covering their ears and going NAHNAHNAHNAH I CAN’T HEAR YOU! over and over again), is that the reason most people accept the official story is because it all hangs together. There aren’t any broken laws of physics involved, merely a misunderstanding of static verse potential energies and how modern structures balance those forces…and what happens when truly huge masses such as those above the plane strike zones of both towers had and begin to shift. Doesn’t even have to be a large shift. Physics 101…potential energy equals mass times height times the gravitational constant. Kinetic energy equals .5 times the mass times velocity squared. Force equals mass times the acceleration. psikeyhackr is right about one thing…it is all just physics. Oh, it’s a lot more advanced when you get into materials science, structural engineering, metallurgy and all the rest, but the basics to understand the collapse are all there. What he doesn’t seem to grasp are the scales of things, how very very much mass was moving initially. Only a small movement but it produced staggering forces. Enough to literally pulverize the buildings like Thor’s hammer.

Kausel also reported that he had made estimates of the amount of energy generated during the collapse of each tower. “The gravitational energy of a building is like water backed up behind a dam,” he explained. When released, the accumulated potential energy is converted to kinetic energy. With a mass of about 500,000 tons (5 x 108 kilograms), a height of about 1,350 ft. (411 meters), and the acceleration of gravity at 9.8 meters per second 2, he came up with a potential energy total of 1019 ergs (1012 Joules or 278 Megawatt-hours). “That’s about 1 percent of the energy released by a small atomic bomb,” he noted.

The M.I.T. professor added that about 30 percent of the collapse energy was expended rupturing the materials of the building, while the rest was converted into the kinetic energy of the falling mass. The huge gray dust clouds that covered lower Manhattan after the collapse were probably formed when the concrete floors were pulverized in the fall and then jetted into the surrounding neighborhood. “Of the kinetic energy impacting the ground, only 0.1 percent was converted to seismic energy,” he stated. “Each event created a (modest-sized) magnitude 2 earthquake, as monitored at Columbia University’s Lamont-Doherty Observatory, which is located about 30 kilometers away from New York City.” Kausel concluded that the “the largest share of the kinetic energy was converted to heat, material rupture and deformation of the ground below.”

And here is how science works…unlike the CT truther types, they actually DO look at all of the various theories that are plausible:

How the Towers Fell

Given the lack of firm conclusions regarding how the collapses occurred, the M.I.T. panel participants asked their audience to consider various theories they put forth. In general, it was agreed that as the structure warped and weakened at the top of each tower, the frame, along with the concrete slabs, furniture, file cabinets and other materials, became an enormous consolidated weight that eventually crushed the lower portions of the structure below. The details of how the frame members failed remain under contention.

Professor Connor’s theory focused on weaknesses in how the vertical and horizontal structural members were tied together. During construction, he explained, each prefabricated floor system was lifted into place by a crane and “supported at the ends like a hinge, where they were bolted and welded to the inner and outer framing tubes” so that part of the gravity load went through the core and the other part through the exterior structure. “The floor trusses sat on beams and were tied down so the core was locked to the exterior,” he said. “It was an unusual system and very lightweight. If you lose the connection between them, however, you lose the ability to carry the floor loads and allow the floors to slide back and forth under stress. If a damaged floor system were to fall, it would break the end connections in the lower floors and down and down the floors would go.”

“In my theory, the hot fire weakened the supporting joint connection,” Connor continued. “When it broke, one end of a floor fell, damaging the floor system underneath, while simultaneously tugging (pulling) the vertical members to which it was still attached toward the center of the building and down.” This phenomenon started a parasitic process that accelerated until total failure and the structure fell in on itself, he said.

Eduardo Kausel proposed an alternative failure explanation that he acknowledged was independently developed by Zdenek Bazant, a professor at Northwestern University. “I believe that the intense heat softened or melted the structural elements¿floor trusses and columns¿so that they became like chewing gum, and that was enough to trigger the collapse,” he said. “The floor trusses are likely to have been the first to sag and fail. As soon as the upper floors became unsupported, debris from the failed floor systems rained down onto the floors below, which eventually gave way, starting an unstoppable sequence. The dynamic forces are so large that the downward motion becomes unstoppable.”

Via two simple models, Kausel was able to determine that the fall of the upper building portion down onto a single floor must have caused dynamic forces exceeding the buildings¿ design loads by at least an order of magnitude. He also performed some computer simulations that indicate the building material fell almost unrestricted at nearly the speed of free-falling objects. “The towers’ resistive systems played no role. Otherwise the elapsed time of the fall would have been extended,” he noted. As it was, the debris took about nine seconds to reach the ground from the top.

“It’s difficult to judge which of these failure mechanisms occurred first; probably all occurred and interacted,” said panel member Oral Buyukozturk, professor of civil and environmental engineering at M.I.T… “The prolonged effect of high heat is likely to have led to the buckling of the columns, collapse of the floors, as well as to the shearing of the floors upon the failure the joints.” He noted that videotapes of the catastrophe showed some tilting of the top portion of the south tower before it collapsed. “This indicates the buckling of one building face while the adjacent face was bending [placed into tension].” After that, the upper portions of the tower are shown disintegrating, with “a dynamic effect and amplification process” following that led to a progressive collapse¿“a kind of pancaking or deck of cards effect”¿down to ground zero, Buyukozturk stated.

Kausel addressed the oft-asked question of why the towers did not tip over like a falling tree. “A tree is solid, whereas building is mostly air or empty space; only about 10 percent is solid material. Since there is no solid stump underneath to force it to the side, the building cannot tip over. It could only collapse upon itself.” Robert McNamara said his failure mechanism theory “focuses on the connections that hold the structure together,” but he cautioned that “we really need to wait for a detailed investigation, before we decide if we have to up the code ratings for these connections in signature structures.”

Anyway, I’m sure that those who are convinced that 9/11 is a huge CT and that They Are Hiding Something™ are going to stubbornly remain unconvinced (because, as noted many times, NO amount of facts or data will ever convince them) and those (happily, the majority in this thread) don’t need more convincing, since they already know, but maybe someone on the fence will read through these threads some time and really look at what’s said. This article (which I highly recommend people read in it’s entirety, as it’s really good IMHO) and some of the others posted in this thread and in others like it are excellent ammunition in your own personal bullshit detection guide. Choose wisely folks, because this sort of pernicious ignorance in the face of this level of facts can erode and poison not only individuals but nations as well.

[tomndebb]

@psikeyhackr

How many legitimate architects and civil engineers do you have information on saying anything about 9/11 one way or the other? That is the curious thing about 9/11. It is not like lots of climatologists agreeing on climate change. It is the deafening SILENCE that is so interesting.

Care to provide some links to these legitimate experts?

This is a simple problem and there should be a large majority publicly on one side or the other but that is not the case. It is a large majority not saying a damn thing.

Every member of every study group, (governmental, e.g., N.I.S.T., educational, e.g., MIT or Stanford, or private, e.g., Popular Mechanics), is included in the large number of legitimate architects and engineers.

No legitimate architect or engineer who has experience in this sort of structure has opposed the explanation of the collapse put forth by N.I.S.T.

You take the extremely odd position that if the N.I.S.T. version were accurate, there would be hundreds of experts chiming in to support them. This is nonsense, of course. It is far more likely that if the N.I.S.T. version were false, there would be hundreds of experts rising up to show that it was false.

Dozens of science experiments are described in journals each month. One does not find hordes of scientists leaping up to say, “That experiment worked!” Rather, it is when something false is published that the majority of experts are prompted to review the evidence and join in a chorus of “Bogus!” An easy example is the nonsense case of “cold fusion,” in which the Fleischmann–Pons experiment was immediately subjected to challenge throughout the physics community. The natural reaction of a person, particularly an expert, reading a text that correctly describes an event is to think, “Well, they appear to have gotten that right; I can keep working on my own projects and not waste time writing up challenges to that nonsense.”

Just as you get your physics wrong, make the ludicrous claim that the WTC standing or collapse can be explained by middle school physics or hold out for a silly “experiment” when the evidence is overwhelming that we do not need any such thing, you turn the reality of expert reaction on its head, pretending that the lack of contradiction is, in some foolish way, support for the idea of contradiction.

[tomndebb]

@psikeyhackr

Actually I think it is called lying about what someone is saying and then accusing them of being in error on that basis.

Do not accuse other posters of lying in this forum.

We have been withholding that epithet from your curious screeds; Do not use it against another poster.

[ /Moderating ]

[Mr.Miskatonic]

@psikeyhackr

How many legitimate architects and civil engineers do you have information on saying anything about 9/11 one way or the other?

I personally know quite a few, actually. One I was hanging out in a converted factory apartment and he was noting the large wooden beams that were the support structure. He noted that they used these because large wooden beams are actually pretty good in a fire since they char on the outside but don’t loose structural integrity as the wood inside stays solid and unburnt. They can eventually fail but it takes one hell of a fire to do so. I commented about how the steel in the towers failed and he noted that ‘yeah, unprotected steel sucks in a fire’.

Another point I was chatting with a pair of Mechanical Engineers who are my friends and the subject of some people saying demolitions were involved in the towers. Their words for those who subscribed to those views were…unkind. This was barely 2003 and NIST wasn’t even started yet, and Loose Change wasn’t making trooth all popular and trendy. (when that movie did come out they told me they thought I was making the 911 CTer’s up).

A Civil Engineer who is in the same hobby as me who, while not a demolitionist, has had to oversee several demolition projects. When he found out that some people thought that explosives were secretly planted in the building he stated “do they have any fucking idea how impossible that is?!”

These people were trained professionals and while I don’t know a huge number of them I will say they had no reason to go walking down the street screaming “fire in a steel building can cause structural failure!!!”. There is no need to. It would be like saying racing cars run on the power of lay lines and insisting it is true because racing car drivers and mechanics aren’t writing papers and screaming to the masse on how pushing the accelerator pedal on a car makes it accelerate. To them it is patently obvious.

[dropzone]

@XT

Thought I’d post this since it’s one of my favorite articles From Scientific American…

[truther] TL,DR. [/truther]

[Rick]

XT excellent article.

[RickJay]

I’m not an engineer but perform quality audits on a lot of structural steel firms; it’s one of the industries we’re strongest in. I’ve learned a LOT about steel structures.

Nobody who actually builds steel buildings finds the WTC collapse even the slightest bit surprising. ** There are no Truthers who actually work in structural steel fabrication. ** None. These people know steel buildings and look at the WTC collapse and say “yup, makes perfect sense.”

[XT]

@dropzone

[truther] TL,DR. [/truther]

Well, like I said, it’s not really for them. It’s not really for most of you guys either…you all already know this stuff, so I’m just preaching to the choir for the majority of the boards members. Oh, I hope some read it (thanks Rick :)) and enjoy it as I have, but really it’s for people who are on the fence but are interested enough and have an open enough mind to actually read the article (as well as follow the various discussions on this board now and in the past) and, well, just weigh the evidence for themselves. To me, the evidence is overwhelming. It’s hard for me to even wrap myself around the sometimes ridiculous claims of the Truthers, but you need to in order to fight the ignorance.

My dream is to see the Loose Change idiots, or Jones et al get the Buzz Aldrin treatment some day. I think I could die happy seeing those guys get smacked by someone right in the kisser. Short of that, puncturing their little bubbles here on the board when they pop up like mushrooms has a satisfaction.

[rock_party]

If the reason for the 9/11 attack was to give GWB carte blanche to go into Iraq and steel the oil,
how about he hired OBL to fly the planes into the buildings? Why the need for the “prewired destruction” anyway? Jumbo jets can do the trick without having to leave fingerprints and evidence on every corner of every floor. He could have his cake and have it all blamed on the
evil terrorists.
And CT guys, please explain how much damage you think the fuel laden jumbo jet would
do to the buildings. Weren’t they doing close to cruising speed? Do you think the office sprinkler system would just put that out? I have heard, too some CT’s say there were no planes, all the video of them are hoaxes.

[running_coach]

@rock_party

I have heard, too some CT’s say there were no planes, all the video of them are hoaxes.

Ignoring the fact there were thousands of witnesses on the streets.

If Bush had hired OBL, there’s still the problem of needing 100s or 1000s keeping quiet.

And think of the chaos if AQ could prove they were hired by the US gov’t.

[rock_party]

I’m just asking, why the need for the controlled destruction of the buildings? There are easier,
neater, more believable ways to pin this on Bush. The need for planes and a controlled destruction, “just to make sure”…rings really unbelievable.

[XT]

@rock_party

I’m just asking, why the need for the controlled destruction of the buildings? There are easier,
neater, more believable ways to pin this on Bush. The need for planes and a controlled destruction, “just to make sure”…rings really unbelievable.

Yeah, it would at least be a more plausible CT, though the problem would basically be why would ObL keep his mouth shut? The dude had ample opportunity to tell the world that not only had he pulled off this great attack on the Great Satan, but that the Great Satan had actually PAID HIM TO DO IT…and facilitated it as well. It would have been a series of body blows to the US, not only to have the attack but then to turn around and tell the world we paid this dude to do it. And there would have been no way for Bush to shut him up, since it’s clear we couldn’t find him.

But yeah, this narrative would at least touch the edges of plausibility. It’s actually more internally consistent with what actually happened, since it actually was the planes that dropped the twin towers, really was a plane that slammed into the Pentagon, etc etc. Have everything that actually happened happen in the narrative, but say that it was Bush pulling the strings on ObL and it would be harder to debate it all, since some sort of bullshit fiction could always be made up as to why ObL never ratted Bush out (hell, there already IS a narrative that ObL was killed over a decade ago, or is still alive…just go with the ‘he was actually killed right after 9/11 and the US government has been doing the videos to keep up appearances’ schtick and there you go…Bob’s your uncle ;)).

ETA: Of course, this isn’t how most CTers minds work, and there are very specific reasons (IMHO) as to why the narrative that did emerge, well, emerged.

[Just_Asking_Questions]

@psikeyhackr

Because at least 30% of 8th graders should have been able to explain why the north tower could not collapse like that in 2001 just because of airliner impact and fire.

Yeah, there were a lot of ignorant kids when I was in 8th grade, too. 30% sounds about right.

@psikeyhackr

But I keep forgetting. This site is supposed to be fighting IGNORANCE.

And we are! But you refuse to learn, so we have to keep fighting.

[Mr.Miskatonic]

@XT

My dream is to see the Loose Change idiots, or Jones et al get the Buzz Aldrin treatment some day. I think I could die happy seeing those guys get smacked by someone right in the kisser. Short of that, puncturing their little bubbles here on the board when they pop up like mushrooms has a satisfaction.

Does it help to know that Dylan Avery is pretty much in the poor house having blown all the money he made?

[Skywatcher]

@Mr.Miskatonic

These people were trained professionals and while I don’t know a huge number of them I will say they had no reason to go walking down the street screaming “fire in a steel building can cause structural failure!!!”. There is no need to. It would be like saying racing cars run on the power of lay lines and insisting it is true because racing car drivers and mechanics aren’t writing papers and screaming to the masse on how pushing the accelerator pedal on a car makes it accelerate…

Plus there’s photographic evidence of the aftermath of the Windsor Tower fire, which left approximately the top third of the structural steel hanging off the building.

[Skywatcher]

@XT

My dream is to see the Loose Change idiots, or Jones et al get the Buzz Aldrin treatment some day. I think I could die happy seeing those guys get smacked by someone right in the kisser. Short of that, puncturing their little bubbles here on the board when they pop up like mushrooms has a satisfaction.

Dylan Avery, 2011:

"Where I am now is, I’ve whittled it down to a very basic statement that I think a lot of people can agree on: There was a cover-up of some kind. The only question is what they were covering up, how far [up] it goes, how deep it runs, and how many asses would be on the line if the truth actually came out.

"I still support the movement, [but was sucked into] a hardcore mentality that it was almost too easy to get into back then, because the war had just started and everybody was just so pissed off.

“It was easy to distrust everything because there was nothing you could trust.”

[Patch]

@running_coach

Ignoring the fact there were thousands of witnesses on the streets.

Not at all. The no-planer twoofers claim they saw holograms.

Seriously.

Then there’s the claim that the buildings were nothing more than hollow shells with nothing inside, which is why the debris piles were so small. All those who claimed to work there? They were in on it.

Then, of course, there’s the claim that nuclear bombs were used to destroy the towers… :smack:

And let’s add me to the mix. I’m a registered Civil Engineer. Though I deal with traffic issues and not structures, structural design was part of my education and I find twoofer claims to be full of shit. The planes and subsequent fire brought down the towers. Fire and damage from the WTC collapses brought down WTC7 and several other buildings. A 757 hit the pentagon. And lastly, a 757 went down outside Shanksville, Pennsylvania. The twoof movement has brought nothing to the table except for their incredible ignorance, incompetence, and ineptitude in their analysis of that sad day.

[CurtC]

@psikeyhackr

So you can claim that the change in thickness played not role. What evidence can you provide?

The walls of the perimeter box columns got thicker also. But we are not supplied with that data either.

The core and perimeter columns could have been made out of Krell Metal and it wouldn’t have made a significant difference. The floors are what gave way, and the perimeter columns then had nothing left to hold them upright and got pushed out by the avalanche.

You keep avoiding this idea: the core columns got thicker lower in the structures, but that didn’t matter one whit.

For one thing, by the time the collapse avalanche had reached the lower parts of the structure, it was giant and unstoppable. For the other thing, the parts that failed were the floors. Each floor was the same and the lower ones were not stronger.

[Trinopus]

@XT

Well, like I said, it’s not really for them. It’s not really for most of you guys either…you all already know this stuff, so I’m just preaching to the choir for the majority of the boards members. Oh, I hope some read it (thanks Rick :)) and enjoy it as I have . . .

I read it and enjoyed it, and maybe even learned a little from it. I hadn’t known about the burning of the shredded aluminum of the fuselage, for instance, although I do have enough chemistry (and practical experience) to know that aluminum burns, and brightly. (Ever play with aluminum powder? Whee!)

Thank you for linking it!

[running_coach]

@CurtC

For the other thing, the parts that failed were the floors. Each floor was the same and the lower ones were not stronger.

[psikey] "They weren’t FLOORS, they were LEVELS!!! [/psikey]