The 9/11 Forum

femr2 · by **femr2** on Thu Nov 05, 2009 8:42 pm

peterene1 wrote:So, femr2, can you offer the speed of the LR ejecta and a comparison with the freefalling debris?

There was an estimation earlier in the thread (OP) from OWE and myself, along with calculated terminal velocity from DBB. (Of the south side ejecta)

OWE calculated ~25m/s. I got 27m/s. DBB model calcs were ~28m/s.

I've done some preliminary tracking with the BBC footage, and got...

(Up to 40m/s, though as traversal is in fits and starts, an average around 30m/s would seem reasonable.)

The OP also includes additional graphs and source data.

Direct comparison to free-falling debris would seem unnecessary, as it will be accelerating. Could you clarify why you want a comparison ? When a similar thread for WTC 2 is created, comparison to free-falling debris will be more relevant as the tower ejecta outpaces the free-falling debris for 2/3 of the height of the tower.

Heiwa · by **Heiwa** on Fri Nov 06, 2009 9:42 am

David B. Benson wrote:
Heiwa wrote:0% ejection means that nothing of A or C or B is ejected ...
Yes. I computed this case. Hardly different that 20% mass ejection.

Bazant's diff. equations do not consider them.
It is Bazant & Verdure's ODE and if you bothered to read the paper you will see that mass ejection (or even injection, for that matter) is indeed considered.

Hm, to eject 20% of the elements of the first crushed floor after impact, say 400 tons of ejecta, at velocity, say 50 m/s would require 0.5GJ or almost 50% of the applied energy by the falling mass through the initiation zone.

The available energy of top part, say 33 000 tons, free falling 3.7 m (all obstructions removed) is only 1.2 GJ! So 1.2 GJ is applied to the top floor of the bottom part! Part of that energy is then absorbed as elastic deformation of the top and bottom parts (actually 100% according my calculations) and then the remaining energy (0% in my opinion) is used to inelastically deform elements in both top and bottom parts, rip them apart and compress them. More energy is evidently applied as top part displaces down another 3.7 m, maximum another 1.2 GJ. But to deform, rip apart and compress >2000 tons of composite structure requires much more than 2.4 GJ or 667 kWh. 0.33 kWh to shred and compress a ton of WTC structure is probably 100 times too little!
What do you think, DBB. How much energy is required to shred/compress one ton of WTC?
And then ejection should start! Of 20% of the compressed debris! Sorry! There is no energy left for it!

David B. Benson · by **David B. Benson** on Fri Nov 06, 2009 9:25 pm

Heiwa --- Most of the mass shed was the perimeter walls, which just fell off to the sides, not participating in the crush-down. Dr. G has estiamted that it would only require about 50 MJ to destroy all the bolts in the perimeter walls on one floor. So I fear your calculations are far off the mark.

And once again, you are off-topic for this thread.

Heiwa · by **Heiwa** on Sat Nov 07, 2009 6:43 am

David B. Benson wrote:Heiwa --- Most of the mass shed was the perimeter walls, which just fell off to the sides, not participating in the crush-down. Dr. G has estiamted that it would only require about 50 MJ to destroy all the bolts in the perimeter walls on one floor. So I fear your calculations are far off the mark.

And once again, you are off-topic for this thread.

I find the femr2 post of Thu Nov 05, 2009 6:37 am quite interesting. The ejecta is seen shooting side/upwards (?) at high velocity while the crush front is displacing down at a much lower velocity where the perimeter walls are still intact.

The bolts holding the perimeter columns together are only located at every 3rd floor and of little interest. There are much more bolts holding the spandrels together.

What is of interest (and topic) is of course the initial sideways rate (velocity) of the ejecta out of the structure and how it comes about! How are the vertical gravity forces applied on the rubble (compression) and how do they become horizontal (!) forces that eject the debris sideways? And what mass is involved, so we can calculate the energy involved for ejection? All this when the crush front displaces, actually accelerates down. Interesting stuff!

femr2 · by **femr2** on Sat Nov 07, 2009 11:57 am

David B. Benson wrote:Heiwa --- Most of the mass shed was the perimeter walls

I don't think there has been a detailed study of the actual comparative levels of mass ejecta. You may be right. You may not.

which just fell off to the sides

Hardly. I'm sure the Winter Gardens building would disagree with you there, for one.

not participating in the crush-down.

Aiii.

Dr. G has estiamted that it would only require about 50 MJ to destroy all the bolts in the perimeter walls on one floor.

And larger estimations have also been made, some by you yourself. It is clear that, in order for the perimeter connections (not just the bolts) to shear would either need specific focus, or vastly more energy expenditure in other areas in order to transmit such forces to the perimeter connections. Repeating 50MJ in all discussions since the number was presented is not a great position to place yourself in IMO. A *convenient* number perhaps ?

All of which ignores many other behaviours of course, including the diagonal slice of WTC1, which I note you have not commented upon...
http://the911forum.freeforums.org/wtc-1-diagonal-slice-t193.html

So I fear your calculations are far off the mark.

Oversimplification leads you into to believing in rather inadequate numbers though DBB...

Heiwa wrote:What is of interest (and topic) is of course the initial sideways rate (velocity) of the ejecta out of the structure and how it comes about!

I'll try and quantify.

How are the vertical gravity forces applied on the rubble (compression) and how do they become horizontal (!) forces that eject the debris sideways?

Expelling the air volume will play it's part of course, but it's useful to note the type of materials ejected, and the behaviour, which points to the mentioned separate *crush front* in close proximity.

And what mass is involved

Can try and work it out based on a density estimation, but it won't be *huge*.

, so we can calculate the energy involved for ejection?

I think calculating the energy for the destruction would be a better use of resource.

All this when the crush front displaces, actually accelerates down. Interesting stuff!

I'm not sure what you mean here. What is accelerating ?

Major_Tom · by **Major_Tom** on Sun Nov 08, 2009 7:55 am

A good image to see the difference between OOS nw and OOS sw collapse fronts.

This is pretty early into the collapse.

From the BL thread we have good clips that show details of the OOS nw and OOS sw collapse fronts.

Great video of both nw and sw collapse fronts floor by floor.

http://www.youtube.com/watch?v=1iT7mmmc-YY&feature=channel_page

and 4 good videos at this post

Major_Tom · by **Major_Tom** on Sun Nov 08, 2009 8:22 am

I think it is painfully obvious to some of the posters that if these collapse fronts are natural, they are what I have been calling OOS runaway destruction.

OOS destruction is regional in nature. When we look at the videos in the last post and remember that all row 500, 600 core columns survived at these elevations (and at least some of the 700, 800 columns too), it is obvious that the OOS nw front is different than the OOS sw front. Columns 501 and 601 are less than 40 feet inside this west wall and the pair survived up to 60 stories high with cross bracing still attached.

An OOS runaway destruction process will have it's own mechanics based on the nature of the OOS floor structure and the completely rubblized driving mass.

Both core and perimeter columns act only to guide and channel the rubblized driving mass AND DO NOT CONTRIBUTE TO STRUCTURAL RESISTANCE FORCE F.

This would be a unique feature to OOS mechanics as opposed to the Bazant (and co.) papers.

Core and perimeter structures are bypassed in OOS mechanics and only OOS flooring, contents and it's connections can contribute to resistance of the lower portion to being destroyed.

In a very tricky way OOS mechanics can ignore the strength of vertical structural supports (columns).

peterene1 · by **peterene1** on Sun Nov 08, 2009 8:29 am

A dust jet emerges from the west face (northern part) at about the same time the OOS sw front reaches that location, thre's no visible activity between them.

Major_Tom · by **Major_Tom** on Sun Nov 08, 2009 8:49 am

Exactly. The OOS sw collapse front seems to line up with some ejections on the northern half.

peterene1 · by **peterene1** on Sun Nov 08, 2009 12:10 pm

Maybe HVAC can explain that? :lol:

Heiwa · by **Heiwa** on Sun Nov 08, 2009 1:20 pm

femr2 wrote:
All this when the crush front displaces, actually accelerates down. Interesting stuff!

I'm not sure what you mean here. What is accelerating ?

Increasing velocity of BLGB crushing down due gravity force. Example:

When WTC 1 upper part C allegedly (according BLGB) crushes the top, 95th, floor, the downward velocity of the crush front (the already crushed 96th floor) is only, say, 8 m/s (it has just started), so it takes, say 0.5 sec to crush the 95th floor and to eject material at whatever velocity. In my opinion the destruction should have stopped then, but let's assume it continues.

So, when the crush front (and 80 m of rubble behind it) has reached floor 1, its velocity may be 40 m/s according BLGB, so crushing the last floor takes only 0.1 sec. Logically the velocity of ejected material must then be 5 times greater. Or 5 times less material is ejected?

I have to say that I cannot visualize a vertical crush down + ejections of a complete structure by a weak top part + rubble taking place at increasing velocity more than 5 times.

Anyway - ejection velocities should be much smaller up top than halfway down and at the bottom of crush down, if only gravity is involved. If observed ejection velocities are constant at any height of the structure, I suggest other energy is applied in the process.

Trippy · by **Trippy** on Sun Nov 08, 2009 5:06 pm

Major_Tom wrote:A good image to see the difference between OOS nw and OOS sw collapse fronts.

This is pretty early into the collapse.

Is that Core material sticking out the top?

femr2 · by **femr2** on Sun Nov 08, 2009 5:16 pm

Trippy wrote:Is that Core material sticking out the top?

If I'm looking at the feature you mean...

No, it's the odd NW corner remnant.

peterene1 · by **peterene1** on Sun Nov 08, 2009 5:23 pm

the top of the corner is at the former 97th or 98th floor

Trippy · by **Trippy** on Sun Nov 08, 2009 5:38 pm

femr2 wrote:
Trippy wrote:Is that Core material sticking out the top?

If I'm looking at the feature you mean...

No, it's the odd NW corner remnant.

The bit that sticks up though the dust, slightly to the right of the visible corner?

Cool.

Presumably the diagonal strips are image artifacts?

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