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.
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.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.
are you supporting mendel who believes the structure exerts and 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.what is the upward force?
No. That's a serious misconception. There is no absolute insignificance. You haven't spelled out what it is insignificant to.insignificant is insignificant.
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.seriously it is.
I don't think it's important, but if you are going to dismiss something, then you need to explain your dismissal correctly.insignificant to the understanding of the collapse of the WTC. Let's be real
Which I just don't think was a very good rebuttal to @Mendel's point.There is no upward force if a load is removed from a structure.
"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.insignificant to the understanding of the collapse of the WTC. Let's be real
Yes, it moves up.You remove weight on top of the table and the table moves up? Practically speaking this is nuts.
Please substantiate your guess! I think it's 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?
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.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.
Not really, it's just going to be a bunch of noise. Not discreet events.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.
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.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.
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".Mendel asks:
NIST explicitly ruled this scenario out as the initiating event - it was FEMA's initial hypothesis.
<< 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.Rather, NIST believes that FIRST external columns buckled. More external columns, then core columns would follow.
<< Exactly.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)
But it could be any of:
- Low resolution
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.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.
...your reasoning does not fit with the actual collapse mechanism:...The sound level would be of a scale literally "unheard of", compared to any CD you can watch (or listen to).
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".It was several floors of columns that would have had to be prepared with explosives and go off at almost the exact same moment.
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