The 9/11 Forum

Spreadsheet calculation based step-wise crush-down model, with an interactive OpenGL 3D front-end.

Resources

Website: http://femr2.ucoz.com
Spreadsheet: http://femr2.ucoz.com/load/1-1-0-9
YouTube Playlist: http://www.youtube.com/view_play_list?p=22FAFC72D202A6D7

The OpenGL application is not available for download at the moment, but will be released when changes to the calculation model stabilise.

OneWhiteEye wrote:

femr2 wrote:A Sauret overlay freefall vid is up btw (Not perfect, but feedback will help steer the next one)
http://www.youtube.com/watch?v=VFrxfH0UGOo

Awesome! Thank you very much.

It matches up better than I thought, at least early on. The only feedback I have at this time is to try a view location 1560m away from the building vertical centerline and 415m below the roofline (scaled according to whatever your world coordinates are). That's a minor suggestion, and not at all important.

It's a free-form camera at the moment, but I like the idea of using a "real-world" viewpoint.
I'll add it to the to-do list.

http://www.youtube.com/watch?v=2hNGHGuYC-w&feature=PlayList&p=22FAFC72D202A6D7&index=2

Anyone fancy explaining how the debris ejecta on the right hand side of the Tower is so far ahead of the simulated free-fall descent ?

Uh, what a sensation, the freefalling debris are/were far lower than the ejecta....

The lowest stuff ejected on the far right is from around the SW corner.

If you look at the same stuff coming from the NW corner you will see the SW leading the NW by 10 to 20 stories most all the way down.


So the "crush front" can have up to a 20 story altitude difference in a mere 208 foot horizontal displacement.


Considering this, It may be correct to see the south side "chute avalanche" as a very independent, practically "decoupled" event as the north side one.

How can the two crush fronts be firmly coupled being from 10 to 20 floors apart? They may be two separate events.


Further, it can be easily shown that the surviving column groups stretched at least 75% across the core in the east-west direction (probably more). This shows the S and N avalanches were quite decoupled, quite independent.

Major_Tom wrote:The lowest stuff ejected on the far right is from around the SW corner.

Just for clarity, I don't view the ejecta as coming from the corner. The video below is a lot closer and shows the ejecta emerging from a much more central location, rather than the corner.
http://www.youtube.com/watch?v=zb1PfiBT7A0

Bad angle to tell what the depth is. From the NW is the way to go. I don't want to insist it is from the corner. There is a massive NS variation in crush front altitude at any moment.


Note: I suspect "crush-front" is a bullsh*t word. I am not arguing against demo.


Some of my favorite WTC1 clips below but I'm sure you have your own.

http://www.sharpprintinginc.com/911/index.php?module=pagemaster&PAGE_user_op=view_page&PAGE_id=56&MMN_position=142:142

Major_Tom wrote:Bad angle to tell what the depth is. From the NW is the way to go. I don't want to insist it is from the corner. There is a massive NS variation in crush front altitude at any moment.

Note: I suspect "crush-front" is a bullsh*t word. I am not arguing against demo.

Re angle...This any clearer for you ?
http://www.youtube.com/watch?v=KixTSW-yOFk

Regardless, can you think of a natural mechanism which would traverse so fast ? (Especially given that the full mass of the 'pile driving mass' cannot be applied, and the corner of the building is especially, er, strong.)
It's behind the free-falling debris alongside, at the freeze-framed time, though it's actually ahead of it earlier in the clip.
The rate of traversal is also very linear. I have to do a better video, but this one shows the linear rate:
http://www.youtube.com/watch?v=BMeTGfCZWMI

Regardless, can you think of a natural mechanism which would traverse so fast ?

I understand JREF can leave you shell-shocked. You have me confused with being a "debunker". I'm arguing for demo, too.

Major_Tom wrote:

Regardless, can you think of a natural mechanism which would traverse so fast ?

I understand JREF can leave you shell-shocked. You have me confused with being a "debunker". I'm arguing for demo, too.

Not at all. I'm simply asking for explanation, that's all. It may have been a topic already discussed here. Have a feeling I keep grabbing your videos too

Perhaps someone who is firm upon collapse will try to explain.

femr2, considering the west wall, there are a few more strange properties I'd like to add.


1) Evidence for peeling as a single sheet for at least 50 floors from floor 94 downwards.

http://www.sharpprintinginc.com/911/index.php?module=pagemaster&PAGE_user_op=view_page&PAGE_id=97&MMN_position=231:231


2) The highest surviving columns were from the far west side of the building. They stand about 70 stories high and are located only about 40 ft from the west perimeter. These columns had cross bracing attached between pairs, meaning cascading debris did not disturb them. (Will provide proof when requested.)


(and, as mentioned above, you can observe up to a 15 floor separation between different collpase front ejections at any moment).


How do you think all that could happen?

Major_Tom wrote:femr2, considering the west wall, there are a few more strange properties I'd like to add.


1) Evidence for peeling as a single sheet for at least 50 floors from floor 94 downwards.

http://www.sharpprintinginc.com/911/index.php?module=pagemaster&PAGE_user_op=view_page&PAGE_id=97&MMN_position=231:231


2) The highest surviving columns were from the far west side of the building. They stand about 70 stories high and are located only about 40 ft from the west perimeter. These columns had cross bracing attached between pairs, meaning cascading debris did not disturb them. (Will provide proof when requested.)


(and, as mentioned above, you can observe up to a 15 floor separation between different collpase front ejections at any moment).


How do you think all that could happen?

Looks to be a factor you've looked at in detail, so I'm not making conclusions....however, I'm having difficulty personally validating the peeling behaviour described. I've spent a day or so processing video's to try and emphasise the detail, filter out the dust...all sorts. I can certainly see where you are coming from, especially the apparent hinging of the large laterally displaced sections, but I still can't see through the dust, so to speak. I'll keep looking. From what I HAVE seen so far on this specific behaviour, the peeling does not seem to comprise the full face width at all, but only partial sections, and I have not yet determined whether the behaviour of the large sections precludes them being separated and free-falling. (I would expect significant behavioural difference between a separated falling body to one connected to a peeling mass)

Again, I'll keep looking. Am not in a position to agree/disasgree how that particular behaviour could happen, though I think specific focus on the building corners would need to be performed...

Do you have an answer ? I'd be interested in your explanation.

Hi femr,

Your calculated total mass above grade is 362x10E6 kg. I have calculated 281x10E6 kg and I think I have resolved most of the minor differences between our estimates. I think the main difference is that you have chosen live loads of 50 and 75 psf respectively for the core and outside. Are you aware of the research (Culver, 1976; Choi, 1989) indicating that in-service live loads (actual loads) are usually to 25% of design live load?

/Greg

Hambone wrote:Hi femr,

Your calculated total mass above grade is 362x10E6 kg. I have calculated 281x10E6 kg and I think I have resolved most of the minor differences between our estimates. I think the main difference is that you have chosen live loads of 50 and 75 psf respectively for the core and outside. Are you aware of the research (Culver, 1976; Choi, 1989) indicating that in-service live loads (actual loads) are usually to 25% of design live load?

/Greg

I've set the loads to their maximum rated loads in order to provide as much mass as possible for collapse progression. It's very easy to change the values to lower values. I'd recommend adding the multiplier to the separated live load columns on sheet Tower. (I'll add a specific floor by floor modifier in the next release...just added it to my local version now.)

Do you want to see a scenario video with 25% live loads ? No problem if you do. Free-fall, or another configuration ? I'm also happy to render video of any configuration if you upload the spreadsheet somewhere. (It makes very little difference to freefall obviously, but does affect more involved scenarios)

femr2 wrote:
http://www.youtube.com/watch?v=2hNGHGuYC-w&feature=PlayList&p=22FAFC72D202A6D7&index=2

Anyone fancy explaining how the debris ejecta on the right hand side of the Tower is so far ahead of the simulated free-fall descent ?

Great work femr!

Doesn't this scenario include conservation of momentum? It matches my "conservation of momentum only" scenario almost exactly. That would explain the difference between the free-falling ejecta and the model.

Photographical evidence indicates that most the core columns buckled over three floors and the exterior broke in huge sections. This would be one reason why the model is slightly slower.

I assume you are using an inelastic collision iteratively with the mass of each impacted floor. Another interesting factor is that the collisions are not really completely inelastic. It might complicate the model too much, but including the coefficient of restitution would allow us to examine different possibilities within the realm of partially elastic collisions. The effect would essentially be less energy loss, which is more realistic. The big question is...how much?

A comment on realism. It is necessary to choose between concrete crushing and conservation of momentum. Concrete crushing is inherently included in conservation of momentum.

Here's my spreadsheet if anyone wants to check the calculations:

http://www.cool-places.0catch.com/911/c ... pse_v3.xls