# Does Seismic Evidence Imply Controlled Demolition on 9/11

#### Jeffrey Orling

##### Senior Member
deformation is not spring loading... if the material is not elastic. Regardless unload a column of the loads of the floor area attached to it is insignificant.

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#### Mick West

Staff member
This is obvious for the plane hitting the building, but it also occurs when a floor detaches: the loss of weight is a sudden upward force that gets added to the column (or rather, a downward force getting subtracted), and would be expected to cause a seismic event at the time, and it doesn't require the falling floor to actually hit anywhere.

Floors don't magically detach though. The force needed to detach a floor is a downwards impulse that several (6-12) times greater than the static force supporting the floor.

And these floor detaching events don't happen at discreet intervals. There's thousands of tons of stuff falling, randomly stripping floors from columns all over the place. And seismic signal would just be noise.

#### Oystein

##### Senior Member
deformation is not spring loading... is the material is not elastic. ...
All of this is wrong.

#### Jeffrey Orling

##### Senior Member
All of this is wrong.

explain...

are you supporting mendel who believes the structure exerts and upward force?

#### Mick West

Staff member
Perhaps you should draw a diagram. It seems like a pretty moot point to me. If an object is on a table then there's an upward force. But what does it matter?

#### Jeffrey Orling

##### Senior Member
what is the upward force?

#### Oystein

##### Senior Member
explain...

are you supporting mendel who believes the structure exerts and upward force?
Absolutely, yes

It has been explained to you: The static load exerts a downward force on the column - the column exerts an upward force that is equal and opposite. Thus, the column is in (elastic!) strain. You remove the load (stress), and the strain bounces back.

A seismic wave results from a change in force (stress, strain). Unloading is a change of force (stress, strain).

(Again, I make no claim about the magnitude of such the seismic signal that would result from detaching a floor, and allow it might be "insignificant" relative to something. It may or may not be measurable by a seismograph. I agree with Mick that the events that lead to the unloading - such as overloading of floor truss seats - are probably greater in magnitude than the detaching itself, and in that sense Mendel's effect is, in practice and in the specific case of the WTC collapses, probably rather indignificant. It could conceivably be significant if someone proposed the hypothesis that the twin towers were demolished by devices that cut the floor trusses or their seats.)

#### Jeffrey Orling

##### Senior Member
insignificant is insignificant. seriously it is.

#### Mick West

Staff member
what is the upward force?
Essentially spring loading, the nature of which depends on the supporting object/material. A table, for example, might bend in the middle. In idealized physics, this is often simplified to the "normal force," but it's still essentially a force from compression. In stiff materials, it's still the intermolecular van der Waals force.

If you were to instantly remove a 100 ton force from a column, then you can't seriously say nothing will happen to the column.

But as I noted earlier, it's not really relevant. There's going be thousands of impacts, deformations, loadings, and unloadings going on during the collapse. You can't simplify it to "a floor" unloading from "the core". That's not what happened.

#### Oystein

##### Senior Member
insignificant is insignificant.
No. That's a serious misconception. There is no absolute insignificance. You haven't spelled out what it is insignificant to.

seriously it is.
Assuming you sit on a chair. Gravity pulls your body mass down - that's called weight. Your body ought to accelerate towards earth's core at a rate of g because of the gravity force. What keeps your body from falling? -> An equal and opposite force.

And now you tell me you don't know what force that is??

Magic.

#### Jeffrey Orling

##### Senior Member
insignificant to the understanding of the collapse of the WTC. Let's be real

You remove weight on top of the table and the table moves up? Practically speaking this is nuts.

What is the significance of a floor breaking apart and dropping in the twin towers in terms of upward force of a column which lost 1/10,000 (guess) of its superimposed load?

#### Mick West

Staff member
insignificant to the understanding of the collapse of the WTC. Let's be real
I don't think it's important, but if you are going to dismiss something, then you need to explain your dismissal correctly.
You said:
There is no upward force if a load is removed from a structure.
Which I just don't think was a very good rebuttal to @Mendel's point.

#### Oystein

##### Senior Member
insignificant to the understanding of the collapse of the WTC. Let's be real
"Understanding of the collapse of the WTC" is the topic neither of this thread nor of this current particular line of discussion. We are talking about seismic evidence, and Mendel wondered (I paraphrase) if the mere unloading of columns during the columns would create a measurable seismic signal. So the signal would, in context, be significant if it can be measured and discerned by any of the seismographs available on 9/11.

You remove weight on top of the table and the table moves up? Practically speaking this is nuts.
Yes, it moves up.
Practically speaking, this creates a ground wave, and is nuts only if you figure that ground waves are nuts.

What is the significance of a floor breaking apart and dropping in the twin towers in terms of upward force of a column which lost 1/10,000 (guess) of its superimposed load?

I'd leave it to Mendel to explain where he wanted to go with his idea. I am here merely to help you understand truly the most basic physics of civil engineering.

#### Mendel

##### Senior Member.
Floors don't magically detach though. The force needed to detach a floor is a downwards impulse that several (6-12) times greater than the static force supporting the floor.

And these floor detaching events don't happen at discreet intervals. There's thousands of tons of stuff falling, randomly stripping floors from columns all over the place. And seismic signal would just be noise.
The very first floor detaching, why does it detach? Because the steel supports are weakening, and they can't take the weight any more, so it is actually the weight of that first floor that detaches it, and not an external downward impulse.

@Oystein I was speculatimg to what could cause a seismic signal that precedes the actual collapse. Mick makes the point that the detached floor is going to hit something shortly, and that's going to cause a bigger signal than the detachment did. So floors dropping down domino style would cause a sequence of impulses resembling a controlled demolition, right?

The info is from NIST. This is 22 minutes before the final collapse, and that would have left a seismic trace of some kind as well; if it was several floors collapsing, another sequence.

Everything going on in the tower that involves large masses moving is telegraphed to the ground through the central support column, and could be tracked by a sufficiently sensitive seismograph nearby.

#### Mick West

Staff member
Everything going on in the tower that involves large masses moving is telegraphed to the ground through the central support column, and could be tracked by a sufficiently sensitive seismograph nearby.
Not really, it's just going to be a bunch of noise. Not discreet events.

#### Jeffrey Orling

##### Senior Member
The floors did not likely detach domino style. There is not evidence that there was a sequential dropping caused by the simultaneous failure of every truss connection at both the facade and the belt girder surrounding the core. Once an area on a floor region was over loading that region would locally collapse.. and this would repeat below.

#### Oystein

##### Senior Member
What Jeffrey says, I think, can also be expressed as "floors did not drop evenly and horizontally, nor in their entirety, they razer zipped of - rapidly, but truss seat by truss seat".

I believe there exist observations that the floor came down at different rates in different corners of the same tower.

All this would result in a noisy seismic track, as Mick suggests.

NIST explicitly ruled this scenario out as the initiating event - it was FEMA's initial hypothesis.
Rather, NIST believes that FIRST external columns buckled. More external columns, then core columns would follow. Wall sections passing inside the still-standing wall below would soon hit floors and cut/punch them out like blunt blades. That is what got the "pancaking" started. (Where falling wall dropped outside of standing wall below, the standing wall would cut falling floors from falling walls)

#### Jeffrey Orling

##### Senior Member
The floor collapses were not because the columns they were connected to failed... but their connections failed and the slabs themselves were crushed by falling debris from above.

#### econ41

##### Senior Member
I continue to recommend keeping a clear distinction between the stages of collapse. In this case:
Stage 1 - "initiation" which ended when the "top block" was falling bodily;
Stage 3 - "progression" still IMO best described as "runaway open office space destruction" despite the emotive and bigoted rejection that description has led to in other forums.

With Stage 2 - a transition from one to the other. Defining the exact lines is difficult - probably not possible BUT the issues being discussed here and somewhat confused/conflated can and should all be placed distinctly into one of the three.

What Jeffrey says, I think, can also be expressed as "floors did not drop evenly and horizontally, nor in their entirety, they razer zipped of - rapidly, but truss seat by truss seat".

I believe there exist observations that the floor came down at different rates in different corners of the same tower.

All this would result in a noisy seismic track, as Mick suggests.
Agreed all three. The observations of different collapses in "zones" recorded in the work of Major_Tom and accessible if needed. The relevant aspect for this thread is that the progression stage "pancaking" was definitely not a sequence of floors each falling as a discrete flat single slab.

So lets clarify some bits of "stage confusion" and related misunderstanding:
NIST explicitly ruled this scenario out as the initiating event - it was FEMA's initial hypothesis.
Mendel's explanation is of "what started the detaching of floors" and is an aspect of the transition stage. Mendel's description "Because the steel supports are weakening" is either ambiguous or wrong." If he means columns weakening - it is wrong...column weakening occurred earlier as the driving process of initiation stage. If he refers to joist to column connectors then "weakening" is still wrong... they did not weaken - they were sheared by overwhelming force. And the comment "...so it is actually the weight of that first floor that detaches it, and not an external downward impulse." is wrong on both points. It was a large proportion of the Top Block weight which caused shearing off of those first few floors. AND that weight of top block was "an external downward impulse".

Oystein correctly describes it in words in his final sentences and the following graphic puts those words into a picture:

The yellow arrows show the "movement" of the perimeter columns - still structurally intact and imposing the "blunt blade" effect as stated by Oystein. The blue lines showing the location of the impacted floors. (And yes it is "worst case" but the same principle applies to the other three orientations.)

So this is how Oystein describes it and his reference to NIST appears to conflate two stages. First this:
Rather, NIST believes that FIRST external columns buckled. More external columns, then core columns would follow.
<< That is definitely "initiation" stage. It is what happend BEFORE the transition we are now discussing. And the next section of Oystein's post is I believe spot on accurate - clearly explaining in words what has been the cause of much confusion over many years. Note however that it was not part of the NIST explanation even tho the sentence follow on could give that impression.
Wall sections passing inside the still-standing wall below would soon hit floors and cut/punch them out like blunt blades. That is what got the "pancaking" started. (Where falling wall dropped outside of standing wall below, the standing wall would cut falling floors from falling walls)
<< Exactly.

And - taking that explanation a step or two further - it is one of the four fatal errors which falsify the Bazant & Verdure "crush down/crush up" model when applied to WTC Twin Towers collapses. The break up of the Top Block occurred at the end of the "transition stage" as "progression stage" was stabilising towards global collapse. i.e. The Top Block did not "ride down" the collapse remining integral to break up in "crush up" after "crush down" was completed. Which is a separate topic but one which rests on the same explanation of the reality of the collapse stages.

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#### Kolle

##### New Member
But it could be any of:
1. Wrong
2. Misinterpreted
3. Misrepresented
4. Low resolution
5. Selective
Hi Karl, welcome to metabunk.

If you think that the camera shaking is significant, or an indicator of a controlled demolition, how is it that the sound of this demolition is not picked up by the same camera's microphone, or indeed any microphone in Manhattan that day?

It would cheer me up no end if someone could invent a way to silence explosions, but to my knowledge no-one yet has.

True story. It was several floors of columns that would have had to be prepared with explosives and go off at almost the exact same moment. The sound level would be of a scale literally "unheard of", compared to any CD you can watch (or listen to). This was not the case at all, as thoroughly investigated by NIST and can also not be picked up with our own ears.

#### econ41

##### Senior Member
...The sound level would be of a scale literally "unheard of", compared to any CD you can watch (or listen to).
...your reasoning does not fit with the actual collapse mechanism:
It was several floors of columns that would have had to be prepared with explosives and go off at almost the exact same moment.
The initiation stage of collapse for the Twin Towers was by a sequenced cascading failure of columns in axial overload --- triggered by heat weakening*** and driven by load redistribution over a period of several minutes but speeding up exponentially. So it was NOT "at almost the exact same moment".

*** OR "triggered by explosives" if anyone ever makes a plausible case which - if true - would have to be at the trigger stage whether or not it was at other later stages.

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