New guy here: Questions for official hypothesis

Apollo20 said:
Sizzler:

My calculations take care of momentum AND energy conservation. In fact they are BASED on momentum and energy conservation! Each impact DOES slow the descent a little, but the downward velocity increases overall, (just not as much as the free fall case).

For free fall through one story height of 3.7 meters we have velocities of 8.52 m/s after 3.7 meters; 12.05 m/s after 7.4 meters; 14.76 m/s after 11.1 meters; 17.04 m/s after 14.8 meters... and so on.

Now with floor resistance leading to a drain on the KE of 1 GJ for each floor we have a reduction of the free fall velocity at each impact:

For WTC 1 for example:

For the first impact after a drop of 3.7 meters by a mass of say 58 x 10^6 kg the KE is 2.1 GJ. If the energy to collapse the first impacted floor is 1 GJ we still have about 1 GJ of kinetic energy remaining. Now we can work backwards and calculate the new velocity of the upper section as it continues on to the second impact. Using KE = 1/2 Mv^2 we have:

v = Sqrt { 2E/M} or v = 5.87 m/s.

The descending mass now falls the next 3.7 meters starting from an initial velocity of 5.87 m/s (Not zero!). Now we can use:

v = Sqrt{(5.870^2 + (2g x 3.7)} = 10.34 m/s

Hence the upper block strikes the 2nd floor with a velocity of 10.34 m/s

For free fall this velocity, as we have seen, would be = 12.05 m/s

So the collapse continues "at near free fall speed" even though the structure offered great resistance!

You see Sizzler, you HAVE TO plough through calculations like this to REALLY look at the collapse. Just saying I THINK the collapse should have been arrested, or I think it should have slowed is not going to help you understand the collapse...........
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Apollo,

Why are you still using 58 x 10^6 kg, when I have carefully demonstrated that the value was closer to 32.8 x 10^6 kg? That makes me feel like I was wasting my time.

/Greg
 
Sizzler said:
I just trying to get my head around the physics of a progressive collapse. Humour me:)

If I raise a bowling ball 2 feet above a stryofoam board, and place hundreds of more styrofoam boards, spaced 2 feet a part, below the first board, the bowling ball will go through all the boards as long as they are all spaced 2 feet a part and the initial 2 foot drop broke the first board.

Right?

So it wouldnt matter how many boards I place below, the bowling ball would just continue to break through them all.
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I don't know if you ever got a clear response to this. Yes, you are correct.
 
You were unable to shave the weight enough?

GregoryUrich said:
Apollo,

Why are you still using 58 x 10^6 kg, when I have carefully demonstrated that the value was closer to 32.8 x 10^6 kg? That makes me feel like I was wasting my time.

/Greg
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Still enough mass to have too enough energy for, global collapse as seen on 9/11. Due to impact and fire. Darn, what is your point using your estimate for mass when it makes no difference, in fact you could explain more what changes this makes to the other assumptions made for collapse initiation. What would less mass mean for the strength of the less massive steel sections. As in did the energy of the more massive steel structure you are now saying is less decrease the needed energy to overcome and destroy? Is your estimate a double edge sword, you say less and the energy to destroy gets less; or you want it both ways, less and more?

It appears the mass is more than enough to start a global collapse. What do you say? Or do you have some evidence to prove something here?
 
Gregory Urich:

I AM aware of your paper. I used the mass of 58 x 10^6 kg in my example for Sizzler because that was the mass I used (and Bazant used) previously.
 
Gravy said:
Much of what's falling outside the footprint is the exterior columns that are being pushed aside by the falling mass. That mass is pounding the floors from their connections, destroying the core columns, etc. By that time, the collapse has reached a terrific speed. Again, the collapse will continue to the ground after it goes a few feet, not to mention a few hundred feet.

Note the height of the top of the building in the before and after below. That's a couple of hundred million pounds that's fallen 150-200 feet, and adding to its mass as it goes.

http://www.internationalskeptics.com/forums/imagehosting/879046a806108d4b4.jpg
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Seeing those two pictures only reminds me of what an absolutely gorgeous day that was. In the larger scheme of things, I don't suppose the weather really matters, but psychologically, it just provides a bigger impact. To me at least.
 
Sizzler what mechanism would you imagine could cause 50% of the mass of the lower portion of the building to fall outside of its footprint. It is reasonable to assume some of the outer walls would fall outside and in the chaotic collapse some of the material from any part of the building may fall outside of its footprint but 50%?
 
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Jennie C. said:
Perhaps I'm not the surfer I think I am, or maybe I don't click on the pop-ups promising free smilies. But where do you find such fun things. I'd like them for emails.
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They're JREF forum smilies. When you make a post you should see a smilie box to the right. Click "More" and you'll be taken to the happy place where they reside.
 
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Architect said:
Sizzler

You may be interested to learn that Edinburgh University and Ove Arup both published papers which disagreed with some aspects of the NIST findings regarding collapse initiation. In particular both believed that the fire on its own would have been sufficient to cause collapse due to a range of factors including creep and inadequate modelling of fire engineering issues at the time of design. ...
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And indeed there are some professional firefighters who believe that is the key factor.
 
eeyore1954 said:
Sizzler what mechanism would you imagine could cause 50% of the mass of the lower portion of the building to fall outside of its footprint. It is reasonable to assume some of the outer walls would fall outside and in the chaotic collapse some of the material from any part of the building may fall outside of its footprint but 50%?
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That's an upper bound proposed in the paper he's referring to.
 
Architect said:
Sizzler

You talk about the steel structure offering no resistance as if this were a surprise, but bear in mind my comments above regarding how the structure was designed and worked. In short, it couldn't handle the differing load paths caused by a chaotic collapse and hence the resistance would be quite modest.

...
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I think this is the hard thing for people to understand; It was NOT a lattice-grid building. Of course, it really couldn't have been one without it becoming the steel equivalent of Chicago's Monadnock Building. (And I have to tell you the ground floor of that building is just a bit claustrophobic.)
 
Gravy said:
They're JREF forum smilies. When you make a post you should see a smilie box to the right. Click "More" and you'll be taken to the happy place where they reside.
Click to expand...

And even more here.


EDIT - I stand corrected. Gravy already covered this. I just didn't notice the toggle between generic smilies and the rest. Oops!
 
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Jennie C. said:
Perhaps I'm not the surfer I think I am, or maybe I don't click on the pop-ups promising free smilies. But where do you find such fun things. I'd like them for emails.
Click to expand...

As has already been mentioned above, those are JREF smilies and there are quite a lot of them in various categories. There are a gazillion different ones elsewhere online, as well, which you can find by searching for "smilies" or "smileys", but here are a few sites:

http://www.freewebby.com/
http://www.clicksmilies.com/
http://www.freesmileys.org/free-animated-smileys.php

Enjoy!

/OT
 
eeyore1954 said:
Sizzler what mechanism would you imagine could cause 50% of the mass of the lower portion of the building to fall outside of its footprint. It is reasonable to assume some of the outer walls would fall outside and in the chaotic collapse some of the material from any part of the building may fall outside of its footprint but 50%?
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OOOO! Me, Me!!! I'll take this...

That's 50% or more of the perimeter columns and not the whole building. Here's why...

The top section fell/funneled inside the bottom section pushing the perimeter columns out until they ripped apart into smaller sections. The perimeter columns leaned out in sections like the sides of a mike carton after the corners are sliced open. So the perimeter columns above SHAVED the floor connections of the bottom on the way down. The lower perimeter columns would have acted as a guide for the top section. The evidence for this is on my site.

http://www.debunking911.com/collapse.htm

I have strong evidence for the total wieght of the top block landing on the floors below and not just one or two floors landing on one.

I can make a case for the top crushing down inside the lower section.



 
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Thanks you guys for helping me understand progressive collapse.

I think I have finally wrapped my mind around it in theory.

Someone wrote that we must consider each floor, one at a time, instead of all the lower floors acting as a single unit. This is because each floor truss connection breaks one at a time, kinda like the stryofoam board example I posted earlier.

Is this correct?

And if this is correct, why does the vertical core collumn unit, which is an independant structure, fail too?

I feel like the core system would be much for resistant to collapse than the floor truss system.

If we consider a progressive collapse, why doesn't the core offer more resistance than the connections of each floor?

Help me out again guys, thanks.
 
Sizzler,

Parts of the core indeed stood for a few seconds after the rest of structure collapse, but were inherrently unstable - see my note about the interlinked nature of the structure previously.
 
Architect said:
Sizzler,

Parts of the core indeed stood for a few seconds after the rest of structure collapse, but were inherrently unstable - see my note about the interlinked nature of the structure previously.
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Right, but the core offered no additional resistance to the floor truss connections for the majority of the floors.

and the fact that some core columns remained for a few more seconds seems to violate the "crush down" mechanism decribed by bazant.
 
Sizzler said:
And if this is correct, why does the vertical core collumn unit, which is an independant structure, fail too?
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It wasn't an "independent structure". The core columns were incapable of standing on their own. In fact, in WTC construction photos you can see how they had to apply temporary cross-bracing to the core columns until the structure around them was completed.
 
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