New guy here: Questions for official hypothesis

Myriad said:
The analogy I use is to a dam breaking and causing a devastating flood. You investigate why the dam broke. You don't need to investigate why, after the dam broke, the water rushed downstream and destroyed things in its path.
Click to expand...


Or perhaps more pertinently, you don't investigate why the water didn't stop part way down the valley, settle, and flow back into the dam.

-Gumboot
 
Architect said:
Sizzler

It is important to understand how structures are designed when considering the ability or otherwise of the intact lower structure to substantively arrest any collapse of the upper part of the building. And these are necessarily complex.

Newton and others here are more qualified than I to comment on structural modelling, however I will try to summarise the key issues as they apply to your query.

Firstly, be aware that the structure of the towers was composite in nature, relying on the inter-relationship of floor, outer envelope, inner core, and roof level girders for overall stability. Specifically:

- The outer envelope handled the dynamic (wind) loadings and carried half (or so) of the weight of the floors.

- The inner core columns carried the remaining weight of the floors plus provided resistance to the overturning moment induced by the dynamic loadings.

- The floors, which were supported on lightweight trussed girder beams, braced the outer envelope.

- Roof level trussed girders transfered dynamic loads betwixt the outer envelope and inner core.

One of the first things to bear in mind, and usually overlooked by the Truth Movement, is the effect which the loss of one or more elements (whether in part or otherwise) might have on the remaining structure.

Next, you need to bear in mind how the individual structural members are designed and jointed. In particular they will be designed to carry loads in certain directions; a floor, for example, is not designed to transmit vertical structural load paths, and so on.

Now the moment a collapse is initiated, design load paths go straight out of the window. Structural elements will be moving in fairly random, although admitedly downwards, directions. They impact other members at angles, bounce off, and generally go rather chaotic. Now there is no way that the structure will be designed to accommodate this.

For example a column deflecting just a few hundred millimetres will hit a floor which has most certainly not been designed for that kind of suddenly imposed vertical load. The joints between the collapsing column and other elements are probably not designed or sufficient to take the changing load paths as the column rotates in the collapse sequence, etc.

So what we have post-initiation is a highly complex structural scenario which in terms of detailed modelling is just not particularly possible. What we can do, as Frank and other have done, is look at the bigger picture and determine whether there was enought energy to initiate and thereafter maintain the process. But there can't be a model which shows the collapse right down to ground level.
Does that help?
Click to expand...


Thanks for your input. It was very helpful and easy to understand as a layman.

The part I put in bold is the part I am curious about.

I havent gotten through all the material gravy posted yet.

But, do I need to?

Or is the conservative calculation by NIST enough to show that there was enough energy?
 
Sizzler said:
Thanks for your input. It was very helpful and easy to understand as a layman.

The part I put in bold is the part I am curious about.

I havent gotten through all the material gravy posted yet.

But, do I need to?

Or is the conservative calculation by NIST enough to show that there was enough energy?
Click to expand...

I think Greening and Co. showed quite effectively that there was more than enough energy stored in the towers to overcome the resistive forces in the floor load.

To echo what Architect has mentioned, buildings simply aren't designed in such a way as to allow them to arrest any form of progressive collapse once it begins. The two loading scenarios, one static (not moving), and one dynamic (moving) aren't even in the same ballpark when it comes to loads. Consider that resting a 20 kg weight on your foot isn't a problem, but dropping said weight on your foot from 1 meter up is a completely different matter.
 
My next question:

There was more that enough energy in the falling upper section of the building to cause the next floor below it to collapse, and then the next, and all the way to the bottom.

So why didn't the collapse progressively slow down as energy was used up as each floor collapsed?

I keep thinking about pool balls. When the cue ball hits another, it slows down.

So why didn't the collapse slow down?
 
Last edited:
Sizzler said:
My next question:

There was more that enough energy in the falling upper section of the building to cause the next floor below it to collapse, and then the next, and all the way to the bottom.

So why didn't the collapse progressively slow down as energy was used up as each floor collapsed?

I keep thinking about pool balls. When the cue ball hits another, it slows down.

So why didn't the collapse slow down?
Click to expand...


You will receive better, more comprehensive answers from posters more knowledgeable than I, but, briefly, each additional floor adds to the weight of the "piledriver" (Dr. Greening's term). If ten-lb. plates are arranged vertically with a few inches between them, then ten lbs. hits the plate under the top one; twenty lbs. hits the next one; then thirty, forty, and all the while this falling mass is accelerating. You do see that it is speeding up, not slowing down?
 
To add to what pomeroo wrote, the acceleration of the entire mass is due to gravity, which continues to operate during the entire collapse, unlike your pool ball example.
 
Last edited:
pomeroo said:
You will receive better, more comprehensive answers from posters more knowledgeable than I, but, briefly, each additional floor adds to the weight of the "piledriver" (Dr. Greening's term). If ten-lb. plates are arranged vertically with a few inches between them, then ten lbs. hits the plate under the top one; twenty lbs. hits the next one; then thirty, forty, and all the while this falling mass is accelerating. You do see that it is speeding up, not slowing down?
Click to expand...

Thanks for the explanation. Can anyone else add to this?

So my next question is:

Does the collapse actually accelerate?
 
Sizzler said:
My next question:

...
I keep thinking about pool balls. When the cue ball hits another, it slows down.

So why didn't the collapse slow down?
Click to expand...
Gravity was the accelerative force. Billiard balls are set in motion by one strike of the cue and then the system plays out. There is no gravity influence in a horizontal system.
 
Sizzler said:
Thanks for the explanation. Can anyone else add to this?

So my next question is:

Does the collapse actually accelerate?
Click to expand...

Yes. It fell in about four seconds less than the free-fall speed for an object of its cross-section. I can dig out my calculations of that if you need them.

The four second difference was the resistance the building gave to being crushed, which resistance was overwhelmed by the quickly growing momentum of the falling mass.
 
BenBurch said:
Yes. It fell in about four seconds less than the free-fall speed for an object of its cross-section. I can dig out my calculations of that if you need them.

The four second difference was the resistance the building gave to being crushed, which resistance was overwhelmed by the quickly growing momentum of the falling mass.
Click to expand...

Right. That makes sense.

Thanks for clearing up fall times. So it isn't wrong to say near-freefall speed? I mean, that is expected in this kind of collapse, right?

Does anyone have an estimation for the freefall speed through air. I mean, if one were to drop the top section of the building simply through air, what would the fall time be?
 
Sizzler said:
Right. That makes sense.

Thanks for clearing up fall times. So it isn't wrong to say near-freefall speed? I mean, that is expected in this kind of collapse, right?

Does anyone have an estimation for the freefall speed through air. I mean, if one were to drop the top section of the building simply through air, what would the fall time be?
Click to expand...

Assuming the top bit of WTC-1 weighed one-fifth of the total weight of the tower, or 100,000,000 pounds, and that the cross-sectional area in the direction of travel was 43264 sq ft (208 squared), that the drag coefficient was 0.7, and that the height of fall was 1,368 feet, we come up with a terminal velocity of 158 ft/second.

(Calculator is here; http://exploration.grc.nasa.gov/education/rocket/termvr.html )

Calculating the free-fall time with that terminal velocity we get a free fall time of 11 seconds.
 
Sizzler said:
Right. That makes sense.

Thanks for clearing up fall times. So it isn't wrong to say near-freefall speed? I mean, that is expected in this kind of collapse, right?

Does anyone have an estimation for the freefall speed through air. I mean, if one were to drop the top section of the building simply through air, what would the fall time be?
Click to expand...
"Near freefall" is a very vague term. If you took an exam with 110 questions and got 40% wrong, you wouldn't say that you "nearly" got them all right. As Ryan Mackey points out in his Griffin paper, the lower part of the building slowing the collapse by 4 seconds means it's absorbing – and being destroyed by – about 48 tons of TNT-equivalent energy.

Air resistance would play little role in the fall time of such an enormous mass over that distance.
 
BenBurch said:
Assuming the top bit of WTC-1 weighed one-fifth of the total weight of the tower, or 100,000,000 pounds, and that the cross-sectional area in the direction of travel was 43264 sq ft (208 squared), that the drag coefficient was 0.7, and that the height of fall was 1,368 feet, we come up with a terminal velocity of 158 ft/second.

(Calculator is here; http://exploration.grc.nasa.gov/education/rocket/termvr.html )

Calculating the free-fall time with that terminal velocity we get a free fall time of 11 seconds.
Click to expand...
1368 feet would be the top of the building. You've got to measure from by the impact area, so the fall time would be less.
 
Gravy said:
"Near freefall" is a very vague term. If you took an exam with 110 questions and got 40% wrong, you wouldn't say that you "nearly" got them all right. As Ryan Mackey points out in his Griffin paper, the lower part of the building slowing the collapse by 4 seconds means it's absorbing – and being destroyed by – about 48 tons of TNT-equivalent energy.

Air resistance would play little role in the fall time of such an enormous mass over that distance.
Click to expand...

I don't understand your test analogy. Why 40%??


I've seen near-freefall speed claims debunked in two ways.

1. The collapse wasnt near free-fall

2. Although it collapsed at near-free fall, that is to be expected.

I'm just unclear which one is more correct.
 
Sizzler said:
I don't understand your test analogy. Why 40%??
Click to expand...


The difference in times between free-fall and what was observed is 4 seconds, or roughly 40% of the collapse time.

I've seen near-freefall speed claims debunked in two ways.

1. The collapse wasnt near free-fall

2. Although it collapsed at near-free fall, that is to be expected.

I'm just unclear which one is more correct.
Click to expand...


I think the point Gravy was trying to make is that near free-fall is very vague, and can easily be misinterpreted. 4 seconds as a time period is very short, so the fall time could be seen as near free-fall, but when you look at it as a percentage (40%), that is quite a bit of difference.
 
Last edited:
Hokulele said:
The difference in times between free-fall and what was observed is 4 seconds, or roughly 40% of the collapse time.




I think the point Gravy was trying to make is that near free-fall is very vague, and can easily be misinterpreted. 4 seconds as a time period is very short, so the fall time could be seen as near free-fall, but when you look at it as a percentage (40%), that is quite a bit of difference.
Click to expand...

Thanks. That makes a lot of sense.
 
Another question:

If the collapsing floors didn't compound and add to the weight of the "piledriver", how would the collapse have looked?

Lets assume this is possible:)
 
Sizzler said:
Another question:

If the collapsing floors didn't compound and add to the weight of the "piledriver", how would the collapse have looked?

Lets assume this is possible:)
Click to expand...


Well, it really isn't possible, so I am not sure why you are asking this. It is kind of like saying, if we did turn off gravity, how would the collapse look? Is there are larger point behind this question?
 
You must log in or register to reply here.

Back
Top Bottom