The virtually free fall speed

[Wolrab]

Several years ago, I asked some truther how fast loads were redistributed when columns fail. He didn't have an answer (surprise), but one of our resident experts did.

I get the impression that they think the load mills around for a while deciding which pathway to take, then exerts force on the rest of the support structure. When the next column is overwhelmed, there is another pause as the load must find a new pathway. The moral of the story is that gravity is relentless and loads are shifted as close to instantaneously as possible.

 

[patchbunny]

Why would WTC 7 fall straight down to the ground in about seven seconds the same day? It was not struck by any aircraft or engulfed in any fire. An independent investigation is justified - and necessary - for all three collapses.”

Woo-hoo! Found my Stundie nomination for January already.

 

[Carlos]

When one or more columns fail, the load is redistributed with speed of propagation of a mechanical wave through a solid medium.

The failure of a single column overwhelms the adjacent columns, which are likely to fail as well, or not. Then it's possible multiple columns fail in a split second, but truthers are unable to understand this.

The argument that all the columns had to be cut at the same time and bla-bla-bla not make sense.

Furthermore the total collapse time was over 15 seconds if you do not ignore the collapse of the west penthouse.

 

[jaydeehess]

Several years ago, I asked some truther how fast loads were redistributed when columns fail. He didn't have an answer (surprise), but one of our resident experts did.

I get the impression that they think the load mills around for a while deciding which pathway to take, then exerts force on the rest of the support structure. When the next column is overwhelmed, there is another pause as the load must find a new pathway. The moral of the story is that gravity is relentless and loads are shifted as close to instantaneously as possible.

Nooooo, its the "Wiley Coyote" garvity model that is in effect. Nothing previously supported begins to move under a gravitational field until it realizes that support has been removed.

 

[jaydeehess]

If you look at the videos and photos, it's obvious that the collapse was not free fall, so this is a strawman. There can clearly be seen falling debris (in free fall) that has fallen much farther than the collapse point of the building.

Additionally the start of collapse is masked on some views. The central tower can just be seen moving, some time before the outer skin starts moving. If you time based on movement of the outer skin, then the collapse appears to be faster than it really was.

ETA: this photo (below left), conveniently annotated by "truthers" themselves, shows a large chunk of outer skin (circled in red) which if you follow the dust trail has fallen at least twice as far as the top of the collapse (somewhere above the yellow bar), the intact portion probably being higher but obscured by dust/smoke.

In no sense does "virtually free fall" match with the reality "less than half as fast as free fall".

[qimg]http://img86.imageshack.us/img86/452/wtc1corecollapsevc5.jpg[/qimg]

That is all quite true for the towers bob but in the case of the fall of WTC 7 there was measured (by NIST) a short , 2.25 second, period of free fall of at least the points on the north face that were measured.

However this 2.25 seconds occurs 1- 2 seconds after the north face begins to drop and 10-12 seconds after internal collapse initiation. By the time the structure is in this free fall period, the columns at a lower level have buckled to the point of creating plastic hinges that essentially offer no force to counter the gravitation forces on the mass of the upper structure. At some point during this 2.25 seconds it is also probable that many of these column's plastic hinge (the point at which they are kinked in buckling) fractured.

 

[Seymour Butz]

That is all quite true for the towers bob but in the case of the fall of WTC 7 there was measured (by NIST) a short , 2.25 second, period of free fall of at least the points on the north face that were measured.

However this 2.25 seconds occurs 1- 2 seconds after the north face begins to drop and 10-12 seconds after internal collapse initiation. By the time the structure is in this free fall period, the columns at a lower level have buckled to the point of creating plastic hinges that essentially offer no force to counter the gravitation forces on the mass of the upper structure. At some point during this 2.25 seconds it is also probable that many of these column's plastic hinge (the point at which they are kinked in buckling) fractured.

This is as logical an explanation as there can be.

The only thing that would make it more complete would be if one of the smart guys here were to do a quick analysis along the line of:

In the first 1.75 seconds, the north face descended appx 7 ft. So given that the buckling was most likely over an 8 story distance, the ext columns would have seen deflection angles of appx "x" degrees, which is the point that the plastic hinges would have fractured given a column dimension of "y".

 

[beachnut]

... Again I call your attention to the properties of steel, which wicks heat away from the fire and dissipates it all directions through out the structure. Many other much hotter and longer burning high rise fires have not resulted in the catastrophic collapse as WTC7.

...

No sources. Wick?

Yep, I see how the heat wicked away! Good job! Try science next time super truther.

 

[jaydeehess]

This is as logical an explanation as there can be.

The only thing that would make it more complete would be if one of the smart guys here were to do a quick analysis along the line of:

In the first 1.75 seconds, the north face descended appx 7 ft. So given that the buckling was most likely over an 8 story distance, the ext columns would have seen deflection angles of appx "x" degrees, which is the point that the plastic hinges would have fractured given a column dimension of "y".

If an 80 foot section kinked in the middle and the vertical difference is now 73 feet then the angle at the top of this triangle is 24.1 degrees(cosx=36.5/40)
Others check my math, please

The horizontal deflection is then 40 sin 24.5=16 feet

OTOH if the kink was 10 feet from the bottom (or top) of this 80 foot section, the horz deflection would be closer to 10 feet(but my trig either fails me or more information would be needed for this non-equilateral triangle, to get a more precise result)

There would be , if I am correct, three plastic hinges, one at the top of this 80 foot section, one at the kink, and a third at the bottom of the section.

 

[piojunbabia]

Conspiracy theorists claim that the 2.5 seconds of "virtually free fall speed" is the definitive proof that explosives caused the collapse of WTC7. According to them, it would only be possible if eight floors of the building suddenly disappeared.

I totally disagree. To me it's consistent with the scenario of a structural collapse due to instability of the structure (in this case, 7 / 8 floors) caused by successive failures of connections and formation of plastic hinges (at beams an buckling columns). In other words, a structure initially

i agree with you sir, if the plane crashed towards the window, the building would have fall sideways and not downwards. This was intentionally done so that other buildings nearby would not damaged.

 

[TJM]

i agree with you sir, if the plane crashed towards the window, the building would have fall sideways and not downwards. This was intentionally done so that other buildings nearby would not damaged.

And how did that work out for the near-by buildings?

 

[Dragon37]

I never said it fell 100% at free fall, I quoted NIST’s report that 105 feet, or 8 stories of the total 47 stories collapsed at pure free fall – that’s 20% of the building’s height that fell at the speed of an object dropped over the side of a building and falling through nothing but air!

Funny how that happens when the structure has been compromised and the perimeter columns lose their centre of gravity.

And the reality of this admission by NIST is – it is a physical impossibility for 8 massive football field sized floors of a steel framed structure to drop 105 feet at pure free fall – that is, without some well placed and synchronized cutter charges.

This is an assertion not a fact because you fail to provide any supporting evidence such as math, etc.

The papers published by the government drones are mostly fluff, with contradictory nonsense pumped up with helium to appear scientific, and appear to prove something, which they do not. The bottom line of all of these wonderful papers is, "a Global Collapse ensued" - great stuff!

The thing is that there is actually science and scientific testing to back what is in the government or independent support papers. The "truthers" actually don't have a scrap of real science to back whatever it is they believe. Most of them are to lazy to do it when making assertions and appeals to authority are so much easier. Heck they are even too lazy to even put together an actual full theory.

They do not prove how diesel and office contents fire can produce molten steel, which was reported by numerous first responders and reporters on the scene, as steel needs 1000 degrees greater temperature than the temperatures that NIST has admitted were present – NIST accounts for this temperature discrepancy by denying the numerous reports of molten steel, to wit: – John Gross and his disingenuous statements that “I never heard of anyone mentioning molten steel”. What a bald faced liar – there are numerous written and recorded report of exactly that – molten steel in the basements of all 3 towers.

So what is it you are talking about here? What diesel? Planes use a fuel that is similar to kerosene. There was no reported melted steel on the day of collapse and very little, if any, claimed later on. Heated steel, combustibles, and inability to get water on these fires could produce molten steel. There is no evidence that it cannot and there is no evidence of any incendiary at GZ.

And they do not prove how the admitted free fall of WTC7 could have happened, because they would have to re-write Newton's Laws first, and then make up some nonsensical new theory, like their quietly retired "Thermal Expansion" theory... or their "Pancake Theory"... remember those knee-slappers?.

The free fall means nothing. It is a tiny portion of the overall collapse and actually isn't a surprise when you actually understand the sequence.

What building collapse was symmetrical?

Are you serious? Do you know what symmetrical means?
All 3 “collapses” were symmetrical. It almost makes some sense with WTC1 and WTC2, as the buildings were in themselves, symmetrical, or square, lending themselves to a symmetrical failure.

There is nothing symmetrical about any of the collapses.

But WTC7 was asymmetrical, a trapezoid of 330 feet on the long side, and 140 feet on the 2 short sides. For this asymmetrical structure to collapse symmetrically calls for a failure of all steel columns, simultaneously, or it would have crumbled on edge, and then fallen horizontally – which by the way NIST actually called the collapse a horizontal collapse, when all videos show a vertical collapse, straight down, not side to side.

What a bunch of claptrap. Buildings on three sides were damaged and at least three streets were cut off. The PO and Verizon buildings were heavily damaged (Verizon cost over a billion to repair) and Fitterman Hall was seriously damaged.

What types of chemicals were used is open to discussion, there may have been a new unknown chemical used along with some conventional stuff – if it’s the government, they have access to military inventions that we find out about 10 years after they have already used them. However, protected samples of WTC dust have been analyzed to contain unreacted Nano Thermite, a compound of extreme velocity and heat, and available only from government labs.

Oh yes right. Since it wasn't thermite and it wasn't know explosives it has to be some super secret weapon. LOL. More Cter knee-slappery.

Actaully, nano-thermite doesn't burn any hotter. As for velocity ... wtf?

It fell as straight down as the very best of controlled demolitions that have ever been performed. It did not hit “two of the buildings”, the Verizon Building on its West side, and the US Post Office building on its East side incurred only very minor cosmetic damage, mostly from the debris from WTC1, and are still in use today after minor repairs. The 47 story WTC7 was reduced to a 3 story heap in 7 short seconds, 20% of which were actual free fall

What a monsterous pile of lies. Verizon and PO sustained heavy damage from 7 WTC not from WTC 1. There was damage from 1 WTC but not as much as came from 7 WTC.

Again with the damn free fall. You sure think it is important. Considering collapse had progressed quite far before that FFA it is really not as big a deal as you think.

The fires moved from fuel source to fuel source, burning themselves out as they moved to other areas, Once the fire moves on, the steel returns to normal temperatures rapidly, as steel is an excellent conductor of heat. No fire burned in one spot long enough to elevate the steel to anywhere near failure mode.

Rubbish. In fact, you have created a paradox and debunked yourself. If the fire is traveling around the floor and steel is a good heat conductor then the steel will not rapidly cool. No matter where the heat source was the entire steel member would heat evenly until the steel was all one temperature. Steel is not a great heat conductor. Eventually heat will spread throughout the beam but if it spread evenly you would actually have many more collapsing buildings (and you would have a hard time welding it and cutting it with torches)

 

[Sabretooth]

i agree with you sir, if the plane crashed towards the window, the building would have fall sideways and not downwards. This was intentionally done so that other buildings nearby would not damaged.

Um...what?

 

[twinstead]

Um...what?

Because killing 3000 people is one thing, but damaging nearby buildings is a serious no no.

 

[Sabretooth]

i agree with you sir, if the plane crashed towards the window, the building would have fall sideways and not downwards. This was intentionally done so that other buildings nearby would not damaged.

PICTURED: Undamaged Nearby Buildings.

 

[DGM]

i agree with you sir, if the plane crashed towards the window, the building would have fall sideways and not downwards. This was intentionally done so that other buildings nearby would not damaged.

To do this the center of mass of the top section would have to move outside of the buildings foot print. What mechanism do you suppose could do this?

 

[triforcharity]

Nano-ropes and chains attached to nano-machines.

 

[tfk]

GrimFandango,

Oh cripes. Another one…

Or do we already know you by a different name?

“Conspiracy theorists claim that the 2.5 seconds of "virtually free fall speed" is the definitive proof that explosives caused the collapse of WTC7. According to them, it would only be possible if eight floors of the building suddenly disappeared.”

But – NIST does not call this 2.5 seconds “Virtually free fall” they call it FREE FALL –in its purest form, which can occur only when there is NO resistance to the falling object. Get the NO RESISTANCE part?

Does your car suddenly slow down when a bug splats on the windshield?
Does your house bow under the weight of a bird that lands on the roof?

The correct, short answer [i.e., the engineering answer] is "no".
The correct, exact answer [i.e., the physics answer] is, of course, "yes".

See if you can figure out the relevance.

Once again, I’m glad you asked – how about the following Structural Engineers and their comments about the amazing colossal collapsing steel structures of 9/11? (All members of Architects and Engineers for 9/11 Truth, over 1,400 members strong to date)


Alfred Lee Lopez, Structural Engineer
Lic: 6201016289
B.S. Arch. Eng. Lawrence Tech Univ
Holly, MI

[13 additional clueless idiots]

Arthur Nelson, P.E.
Lic: MA PE 32785
M.Sc., Structural Eng, Northeastern
Seekonk, MA

Every profession has incompetents.
Many people are competent within their own field & incompetent out of it.

Notice that I selected all Structural Engineers, not simply Engineers, or even just Architects, in the hope of satisfying your stringent demands from the Truth community. The following is an example of what these people have to say regarding 9/11, and the foolish Official Conspiracy Theory.

They haven't "said" one word about 9/11. Engineers "say things to other engineers" in publications.

Lazy engineers, clearly not sufficiently concerned with the events of 9/11 to put out the work required to construct and publish a cogent argument.

In other words, "hypocrites".

“One of our primary responsibilities as architects and engineers is to ensure public safety in and around our structures, and we take this seriously. It is also our responsibility as concerned American citizens to ask questions and seek honest answers. I encourage everyone to read the numerous books, technical reports and papers about the WTC; look closely at the photographs and videos; listen to the speakers with an open mind. Decide for yourself, and take a stand for what you believe. As a structural engineer I believe in the laws of physics and rely on them every day.

One paragraph of meaningless platitudes.

After much reading and studying it is obvious that NIST, FEMA and the 9/11 Commission have all fallen short of a detailed accounting of the catastrophic collapses of the three World Trade Center buildings in Manhattan on 9/11/01.

Neither FEMA nor the 9/11 Commission were tasked with providing a detailed accounting of the collapses.

Neither was NIST. They were tasked with providing a detailed accounting of the CAUSES of the collapses. This they did.

Your Structural Engineer feels that 10,000 page NIST report is insufficiently "detailed". He is invited to embellish. Or point out what he thinks is wrong.

He has done neither, AFAIK.

A few examples of unexplained details include the "severe high temperature corrosion attack on the steel" as described in Appendix C of the FEMA Building Performance Study,

Wrong.

Completely explained by Barnett, J., Biederman, R., and Sisson, R., JOM, Vol. 53, pp. 12-18.

And subsequently confirmed by R. R. Biederman, Erin Sullivan, George F. Vander Voort, and R. D. Sisson.

the complete symmetrical collapses following asymmetric structural damage

Wrong. The collapse wasn't completely symmetric.
See NIST report.

It was approximately symmetric.
Explanation for approximately symmetric given by Bazant. Le, Greening & Benson

and short-term fires

BLGB, What Did and Did not Cause Collapse of WTC Twin Towers in New York
Journal of Engineering Mechanics ASCE , Vol. 134 (2008),

Nevertheless, it can easily be explained that the stress in some surviving columns most likely exceeded 88% of their cold strength σ0. In that case, any steel temperature ≥ 150°C sufficed to trigger the viscoplastic buckling of columns (Bazant and Le 2008). This conclusion is further supported by simple calculations showing that if, for instance, the column load is raised at temperature 250°C from 0.3Pt to 0.9Pt (where Pt = failure load = tangent modulus load), the critical time of creep buckling (Bazant and Cedolin 2003, chapters 8 and 9) gets shortened from 2400 hours to 1 hour.

and the chemical signature of incendiary compounds found in the toxic WTC dust.

Found by incompetent amateurs.
Your "structural engineer" is far too credulous to be a good engineer.

I would really like to know why complete collapse of the twin towers "became inevitable" as expressed by NIST without any scientific analysis to substantiate it. Why would all 110 stories drop straight down to the ground in about 10 seconds, pulverizing most of the contents into dust and ash - twice? Why would WTC 7 fall straight down to the ground in about seven seconds the same day?

Wow. Sure does ask a lot of questions.
Funny, engineers usually supply answers, when the topic is within their field of expertise. It seems your "structural engineer" doesn't consider his own answers worthy of publication.

It was not struck by any aircraft or engulfed in any fire.

Struck by 100s of tons of debris.
WTC7 was "not … engulfed in any fire"??

Your "structural engineer" seems rather clueless regarding the day's events.

I would be happy to post each and every comment for each, please feel free to ask for them

Well, based upon this posting, it appears that, lacking quality, quantity may be all you have to offer.

tom

 

[Craig4]

Grim Fandango, I'm going to explain this to you and we're going to use some real science here. If there were explosives there has to be explosive residue. It's the Law of Conservation of Matter. Matter can neither be created or destroyed. It's not just a good idea, it's the law. If there was an explosive in the World Trade Center, there has to be residue from those explosives found in the debris. It's already been explained to you that the nano-thermite is not credible and therefore not evidence. So, if there was an explosive, where is the residue? Got any?

On another note, do try to remember that about 3000 people died that day. This is a very serious event. It is not a suitable topic for your silly little hobby and deserves far better than to be turned into a meaningless diversion by you.

 

[BasqueArch]

GrimFandango,

Originally Posted by GrimFandango View Post
Once again, I’m glad you asked – how about the following Structural Engineers and their comments about the amazing colossal collapsing steel structures of 9/11? (All members of Architects and Engineers for 9/11 Truth, over 1,400 members strong to date)

Alfred Lee Lopez, Structural Engineer
Lic: 6201016289
B.S. Arch. Eng. Lawrence Tech Univ
Holly, MI

[13 additional clueless idiots]

Arthur Nelson, P.E.
Lic: MA PE 32785
M.Sc., Structural Eng, Northeastern
Seekonk, MA
......


Many people are competent within their own field & incompetent out of it.
Every profession has incompetents.

Yes, this is proof that of all structural engineers, half are below average.

 

[Seymour Butz]

If an 80 foot section kinked in the middle and the vertical difference is now 73 feet then the angle at the top of this triangle is 24.1 degrees(cosx=36.5/40)
Others check my math, please

The horizontal deflection is then 40 sin 24.5=16 feet

OTOH if the kink was 10 feet from the bottom (or top) of this 80 foot section, the horz deflection would be closer to 10 feet(but my trig either fails me or more information would be needed for this non-equilateral triangle, to get a more precise result)

There would be , if I am correct, three plastic hinges, one at the top of this 80 foot section, one at the kink, and a third at the bottom of the section.

This is a good beginning.

And IIRC, if there are 3 hinges, the middle one will be twive what the upper and lower are, so about 45 degrees if your math is correct.

I guess some generalizations would be relevant here too.

Longer lengths would mean less deflection and fewer degrees of rotation?

How does column fracturing work though?

Larger dimensions fracture at less rotation?

Thicker webs fracture at less rotation?

Discussing the technical issues is about the only interesting part about 9/11 that interests me anymore.