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March 13th, 2016 WTC Seminar Transcript

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This is the full transcript for the March 13th, 2016 seminar held by Aldini10.

(19:22:39) brian54: hello everyone, and welcome to the return of the seminars to simmania !!
(19:23:02) brian54: and we have a really great one this evening , which has been long anticipated for many months ..
(19:23:21) brian54: the topic of tonight's seminar is .. - structural frame of the World Trade Center towers and what led to their collapse!
(19:23:35) brian54: Please a reminder, to hold your questions until after the seminar is over, thanks!
(19:23:47) brian54: So than it is now time to introduce our guest speaker for tonight's seminar ...
(19:24:02) brian54: He would be one of our most popular chat members and everyone knows him im sure..
(19:24:19) brian54: So without further ado than, let us give a warm round of applause too...
(19:24:32) brian54: Aldini !!!!
You have the floor my good friend :) ..
(19:24:51) Aldini10: Thank you very much for that great introduction brian!
(19:25:09) Aldini10: Now we all know that the original WTC complex was destroyed and all this
(19:25:34) Aldini10: people still have questions or are just overall without knowledge of what kept these towers up
(19:26:16) Aldini10: I am here to tell you that these towers did have a unique design at the time of their construction with lots of innovations in construction
(19:26:46) Aldini10: It was quite the project at the time
(19:27:03) Aldini10: no other buildings of their size were thought to be feasible
(19:27:17) Aldini10: but it was all made possible by some really determined people
(19:27:21) Aldini10: REALLY determined
(19:27:51) Aldini10: Okay I will begin with the design of these towers
(19:28:10) Aldini10: the towers were tube in tube towers, meaning that there were only interior columns and exterior columns
(19:28:42) Aldini10: here is a very clear image showing this
(19:29:04) brian54: nice :)
(19:29:13) Aldini10: yes, these towers were mostly air!
(19:29:42) Aldini10: but that picture does not show enough so here is a graphic of a typical floor plan
(19:29:53) mitokey: oh wow
(19:30:29) Aldini10: you can see that there were no supporting columns between the interior core and the exterior columns
(19:30:43) brian54: correct
(19:31:05) Aldini10: You see, these towers were built to have lots of people work in them
(19:31:32) Aldini10: so by getting rid of some columns they were able to have most of the floor space area free
(19:31:56) Aldini10: and that is really good for people who want to build with not a lot of money
(19:32:09) Aldini10: they get more floor space, less construction costs, etc
(19:32:21) brian54: ya :)
(19:32:42) Aldini10: As seen the area of each tower floor was approx. 1 acre in size
(19:33:03) brian54: interesting
(19:33:24) Aldini10: Oh i forgot to mention that all the utilities/elevators were placed between the core columns to not have them obstruct floor space
(19:33:54) Aldini10: here is how a typical floor looked like after construction
(19:34:32) brian54: quite large really
(19:34:43) Aldini10: While construction did not start yet these designers really hit it off with the floor space usage
(19:35:12) Aldini10: but when they did want to build they found out that nearly half of the land where the WTC was to be built was not actually land
(19:35:44) Aldini10: but it was landfill, accumulation of debris and trash which stuck to the existing land adjacent to the Hudson river
(19:35:58) Aldini10: and had accumulated over centuries
(19:36:03) brian54: but not on top of the river right ?
(19:36:40) Aldini10: hold your thoughts please :P
(19:36:48) Aldini10: yes not directly on top of the river
(19:37:07) Aldini10: also, towers are typically really heavy
(19:37:25) Aldini10: so they knew they'd have to dig down to really really hard dense rock
(19:37:44) Aldini10: so this rock was at least 70 feet below ground level
(19:38:04) Aldini10: but they could not dig without the water from the river filling up their newly dug hole
(19:38:38) Aldini10: so what they did was devise a method to construct a huge underground retaining wall 70 feet down
(19:38:52) mitokey: Sorry guys, I have to go to bed now. This is very interesting and wish I could stay up longer. Have a good night and nice seeing you guys again :)
(19:39:00) Aldini10: np mitokey, see ya
(19:39:03) brian54: niters mike :)
(19:39:11) Aldini10: here is a graphic that shows this method
(19:39:23) brian54: thanks for coming ok :)
(19:39:39) brian54: ohhh
(19:39:48) brian54: thats an interesting pic oliver :)
(19:39:49) Aldini10: from left to right, they dug down with a special excavator
(19:40:07) brian54: ya
(19:40:19) Aldini10: and poured in slurry, which is a thick clay like mixture of liquid
(19:40:38) Aldini10: this would get rid of the water in that area of excavation
(19:41:01) Aldini10: once the slurry filled the area they placed huge rebar cages and then poured in concrete
(19:41:21) Aldini10: they did this until the whole area to build the towers was complete
(19:41:58) Aldini10: It was like an inverted bathtub
(19:42:08) Aldini10: here is a close picture of the wall
(19:42:11) brian54: :)
(19:42:27) Aldini10: this picture was taken 70 feel below street level, mind you
(19:42:39) brian54: ya neat pic there :)
(19:42:48) Aldini10: you can see the super heavy cables needed to keep the wall in check
(19:43:00) Ceafus88: I have some pictures of it from when I went to NYC. :) Insane. :)
(19:43:02) brian54: yup
(19:43:09) Aldini10: really awesome stuff
(19:43:18) brian54: it is
(19:43:34) Aldini10: So once they finished with this, they had to completely take out all of the land in the bathtub area
(19:43:37) Darvince: that's some ingenious engineering
(19:43:49) Aldini10: it was filled with about 1 million cubic yards of dirt
(19:43:54) brian54: wow
(19:44:01) Aldini10: they just poured it all across the street into the river
(19:44:12) Aldini10: this crated 88 acres of new land
(19:44:16) Aldini10: created :P
(19:44:31) brian54: heh
(19:44:55) Aldini10: so once they reached the impenetrable rock then could they start working on the actual towers
(19:45:56) Aldini10: Now with the design of these towers, since they were so tall they needed super heavy duty columns
(19:46:17) brian54: ya
(19:46:18) Aldini10: the core columns were the thickest and heaviest, with one weighing up to 55 tons
(19:46:33) Aldini10: and 6 feet by 3 feet
(19:46:50) Aldini10: almost all the column was steel
(19:47:06) Aldini10: these were placed at the lowest level, right on top of the bedrock
(19:47:46) Aldini10: the columns were immense all they way up to the 48th floor
(19:48:01) brian54: right
(19:48:01) Aldini10: here is an image during construction showing the bare steel columns
(19:48:49) Aldini10: Oh yes and all of the structural components were prefabricated in a factory
(19:49:05) Aldini10: every single piece of steel was prefabricated
(19:49:23) Aldini10: and brought to the site at the exact time needed
(19:49:35) Aldini10: there was little time and space to spare
(19:49:36) brian54: wow
(19:49:55) Aldini10: they were like puzzle pieces
(19:50:31) Aldini10: They used only 3 main basic components to build the towers
(19:50:39) Aldini10: First ones are the core columns
(19:50:47) Aldini10: second, exterior columns
(19:51:08) Aldini10: and third were steel trusses to bridge the gap between the columns, forming the huge open floor space
(19:51:52) Aldini10: here is an image showing the immense size of these pieces
(19:52:02) Aldini10: well that just shows the exterior columns
(19:52:16) Aldini10: all columns were at least 3 stories tall
(19:52:27) brian54: ya biggies
(19:52:31) Aldini10: I think the exterior columns were great
(19:52:38) brian54: ya ?
(19:53:10) Aldini10: they were built with very deep spandrel beams, which when placed together would deflect any kind of loads immensely
(19:53:38) Aldini10: these exterior columns carried all wind loads and 40% of the tower's weight
(19:53:50) brian54: wow
(19:54:17) Aldini10: you can see in the image how the steel trusses were placed at the column connections
(19:54:34) Aldini10: all columns and trusses were bolted together
(19:54:57) Aldini10: the trusses were also very flexible, and flimsy looking
(19:55:12) Aldini10: this shows a detail of a typical truss
(19:55:53) Aldini10: Once put together all these pieces created a very strong building
(19:56:20) brian54: ya
(19:56:21) Aldini10: so strong in fact that they decided to design it with airplane impacts in mind
(19:56:23) brian54: im sure
(19:56:31) brian54: ya i heard that
(19:56:51) Aldini10: so the towers were designed to withstand an impact of a 747 airplane flying slow and low to the ground
(19:57:20) Aldini10: engineers claimed they designed it with the airplane hitting it anywhere
(19:57:30) brian54: ah
(19:57:35) brian54: that i didnt know
(19:57:47) Aldini10: but not just because of the exterior and core columns
(19:57:59) Aldini10: there was one special thing constructed at the top of each tower
(19:58:07) Aldini10: it was called a hat truss
(19:58:31) Aldini10: this was a system of diagonal bracings designed to tie together the core and ext. columns
(19:58:46) Aldini10: and to regulate wind stresses
(19:59:00) Aldini10: and to carry the weight of TV antennas
(19:59:25) Aldini10: this was interesting because only one tower was fitted with a communications tower
(19:59:41) Aldini10: and now these towers held up really well over time
(19:59:52) Aldini10: but then came 9/11 as we all know
(19:59:58) brian54: yes
(20:00:03) Aldini10: sad to see those towers go
(20:00:11) brian54: agree
(20:00:14) Aldini10: we all know airplanes flew into them
(20:00:30) Aldini10: the first tower to get hit was tower 1
(20:00:33) Aldini10: then tower 2
(20:00:39) Aldini10: but tower 1 collapsed last
(20:00:47) brian54: right
(20:00:56) Aldini10: let me bring in some points which occurred in both towers
(20:01:07) brian54: sure
(20:01:16) Aldini10: up to 1/4 of tower columns were severed on each tower following airplane impacts.
(20:01:36) Aldini10: and the Hat truss redistributed loads by “hanging” the severed columns and pushing down on the ext. columns
(20:01:58) Aldini10: so whichever columns were severed were literally hanging in there
(20:02:07) Aldini10: thanks to the hat trusses
(20:02:31) Aldini10: without the hat truss i believe each tower would have collapsed immediately
(20:02:41) brian54: oh for sure
(20:02:59) Aldini10: and also when the planes hit there was debris everywhere
(20:03:19) Aldini10: this debris destroyed some fireproofing on columns, leaving them bare
(20:03:28) brian54: right
(20:03:55) Aldini10: and now with the subsequent fires, steel does not fare well in fire
(20:04:27) Aldini10: And also when the planes hit they destroyed supporting floor system which allowed the unsupported columns to warp under pressure of weight and fire.
(20:05:10) Aldini10: now to Tower 1
(20:05:31) Aldini10: the reason why tower 1 collapsed last is because the airplane hit really high up in the building
(20:05:42) Aldini10: it hit between floors 97 and 92
(20:05:43) brian54: true
(20:06:01) Aldini10: now the higher you go up in a building the less there is to support
(20:06:11) Aldini10: and the steel frame is also pretty much barebones
(20:06:29) Aldini10: here is an image that shows the airplane impact
(20:06:36) Aldini10:
(20:06:58) Aldini10: now it hit dead center which severed a lot of the core columns
(20:07:07) Aldini10: but not all of the exterior columns, as seen
(20:07:29) Aldini10: the hat truss did its job until the fires warped the steel and gave way
(20:08:00) Aldini10: i wanted to show this image that shows the very intense fire that burned
(20:08:03) Aldini10:
(20:08:16) brian54: sure
(20:08:20) Aldini10: no doubt the fire was very hot
(20:08:34) brian54: for sure yes
(20:08:38) Aldini10: in fact hot enough to warp all steel in the building at that section
(20:09:02) Aldini10: the fire burned up to 1200F very quickly
(20:09:07) brian54: wow
(20:09:19) Aldini10: this image shows the strength of steel up to 1200C
(20:09:24) Aldini10:
(20:09:37) Aldini10: mind you that 1200F is 650C
(20:09:47) brian54: right
(20:10:03) Aldini10: so by looking at this graph you would think that they should have collapsed much earlier
(20:10:13) Aldini10: well, we will never know
(20:10:13) brian54: true
(20:10:42) Aldini10: Now onto tower 2
(20:10:53) Aldini10: the airplane this time hit much lower than tower 1
(20:11:01) Aldini10: between floors 78 and 81
(20:11:04) brian54: ya i recall
(20:11:21) Aldini10: this meant that the tower had a lot of section above to handle
(20:11:26) Aldini10: a lot of weight, rather
(20:11:50) Aldini10: this picture shows the immense damage sustained by the tower
(20:11:51) Aldini10:
(20:12:30) Aldini10: the green area shows the entire floor was missing
(20:12:35) Aldini10: in those parts
(20:13:03) Aldini10: blue shows where all the airplane debris ended up
(20:13:13) brian54: right
(20:13:19) Aldini10: the circled columns show which ones were damaged
(20:13:48) Aldini10: now that the building was hit off center this meant that all the damage was concentrated on none side of the floor
(20:13:54) Aldini10: one *
(20:14:09) Aldini10: which ultimately is not good for any building
(20:14:18) brian54: ya
(20:14:34) Aldini10: needless to say most of the columns on the right side were left bare from the impact
(20:14:42) Aldini10: and the fire did its job
(20:14:51) Aldini10: this is also something very interesting
(20:15:28) Aldini10: when you look at videos of tower 2 collapsing, you can see it fall forward and twist as a single piece above the impact zone
(20:16:01) Aldini10: i'm sure it was something no one would have ever conceived
(20:16:31) Aldini10: i dont have any links to that
(20:16:40) brian54: right
(20:16:48) Aldini10: hmm yes
(20:16:57) Aldini10: well i was nearly done anyway :P
(20:17:11) Ceafus88: This is amazing, keep going. :D
(20:17:30) Aldini10: well i suppose pretty much done, i've explained how the towers collapsed
(20:17:36) Aldini10: but i forgot some things
(20:18:06) Aldini10: this shows the displacement of tower 2 as it was hit by the aircraft
(20:18:32) Aldini10: the towers would not have been fixable afterwards because of the immense energy released by the plane
(20:18:41) brian54: ya
(20:19:13) Aldini10: with any kind of impact that pushes a tower up to 15" in any direction, the steel skeleton was damaged irreversibly
(20:19:41) Aldini10: after the impacts, pretty much every floor had reports of doors twisted and not being able to open
(20:19:59) Aldini10: the towers were pretty much not straight anymore, they were leaning off center
(20:20:23) Aldini10: you can hear this in a lot of firefighter chatter in videos
(20:20:49) Aldini10: well i think that's it

(20:21:22) Aldini10: thanks for coming and being patient everyone!

Additional questions/comments can be answered here as well.

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Aldini that was an excellent seminar. Very well done and very informative. You did a great job with it. The photos were relevent and were a nice touch.

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I think the seminar went off good..

Aldini did just a marvelous job as guest speaker this time around..

And also we had a peak of 8 people in the room which i think is a decent amount..

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Holy cow those are some fantastic photos. I really appreciate you digging them up to post here! I am sure visiting the museum was a great experience for you. I've heard it's one not to miss if you're in NYC.

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