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The World Trade Center Discussions about the World Trade Center, the original, 9/11 and new redevelopment.



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Old June 12th, 2017, 01:09 AM   #1
DSMissed
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A few questions regarding design and structure of WTC

I have been a lurker on here for many years, and I finally decided to join so I could ask a few questions that I have.

A little about me, I was born and raised in South Dakota. I graduated high school with the same 13 kids I started kindergarten with, in a town with a population of 500. The closest I've been to New York City would be from watching Crocodile Dundee when I was a youngster However, I've always been fascinated with the incredible architecture and design that makes up the iconic skylines of big cities.

Having never been around anything taller than a 4 story Holiday Inn (no joke, don't make fun!), buildings such as the twin towers still baffle me in many ways. I was hoping some of you might share your knowledge of with me, it would be much appreciated!

1. There are a few stunning images of the towers where you can see right through them. Here are two:
http://www.therealnewsonline.com/upl...42681_orig.jpg
https://s-media-cache-ak0.pinimg.com...5116d9558d.jpg

Are these real photos? If so, were the windows still see through even with the bronzed tinting?

Also, in the north tower on that second image, you can see the core very clearly. Is the thicker dark area elevators, and the thinner dark area the stairway?

2. Both towers exterior appears to have two darker stripes around them, and the top few floors appeared darker. How was this affect created? Was it for aesthetic purposes only?

3. What was the purpose of the antenna on the north tower? I know that radio stations used it as a transmitter, but is that all it was used for?

I also read that the radio stations were a tenant on the 110th floor of north tower. Did they have their studios or offices in there? Or was it more of a mechanical floor for servicing the antenna?

4. What equipment was used to supply water, heat, and air conditioning to the towers, and where was the equipment located? Did one facility provide for both towers, or were there separate ones for each? Did each floor have its own water heater? Did the top floors have noticeably decreased water pressure? Was the air temperature in the buildings consistent throughout?

5. Was there both elevator and stairway access on all floors of both towers? Was there any elevator that traveled the full distance to the top floor?

6. From my understanding, the floors were concrete. How thick were the slabs? My understanding is also that movement could be felt in the building on windy days, more prominently closer to the top and further from the core, of course. If this is true, what kept the concrete floors from getting stress cracks? Or the walls, for that matter?

7. According to news articles, the asbestos fireproofing needed to be removed from the towers. Was it in both towers on all floors? What would it have been replaced with, and how would it have been replaced in a way that didn't disrupt tenants?

8. What was the method of securing each tower, and each floor? 24/7 guards working, security cameras, etc? Was each tenant floor locked, or accessible using a passcode, keycard, or something similar?

9. Was the lobby open 24/7? Was the observation deck observable during any weather? Or was it closed if, for example, it was foggy and the view was obstructed?

10. Was there a backup generator capable of supplying power to the entire building in the case of an outage? If so, what was used, and where was it located? Would there have been one for both buildings or one for each, perhaps several spread out in each building?

11. What was the closest distance between the towers? Meaning, the distance between the two closest corners?

12. Did they ever use the top of the south tower to light off fireworks for the 4th of July? Because if they didn't, they really should have.

13. My heart continues to break for all affected by 9/11, including those still living. I was not going to ask this one, but it weighs on me quite often, because I worry about people. Was each tenant required to have some sort of insurance on at least their area of the building, so that each employee, or employee's family, that was effected was able to receive some money to help them recover? Or did the insurance that the owner of the towers was required to carry cover all occupants of the building and those in the destruction path? Or to put it more simply, did the owner or tenants have insurance which provided monetary relief for employees, city workers, volunteers, families, etc that were in one way or another affected due to that awful day?

If not, has insurance requirements on similar structures (at least in NYC) since been modified to cover all occupants?

Last edited by DSMissed; June 12th, 2017 at 01:52 AM.
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Old June 12th, 2017, 11:53 AM   #2
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I may not be able to answer to all the questions and I will probably be wrong at some point but I'm gonna do my best.

1. I believe the windows were just not placed at that moment on the upper floors. The "thick" and the "thin" part contained the elevator shafts and stairways. The separation is just the hallway which allowed the tenants to access the elevators, stairways or restrooms.

2. The darker ares of the towers were the mechanical floors on floors 7/8, 41/42, 75/76 and 108/109. These areas were darker since they had no windows. Instead there were black vents used for ventilation. Additionally, the columns were a bit wider (at the top it was more playful) creating these "bands" going around the building. Yamasaki did probably change the layout of the columns on the 108/109th floor simply for aesthetic purposes.
Vents: http://yankee451.com/wp-content/uplo...-walkway-2.png
Floors 108/109: https://s-media-cache-ak0.pinimg.com...6acd7f6b82.jpg
Other mechanical floors (visible in the lower portion of the picture, unfortunately it's from 9/11): http://www.sharpprintinginc.com/911/...C2_IB_8_53.JPG

3. The North Tower antenna was not only used a radio but also as a TV transmitter, updated in 1999 to support DTV. Most NYC tv broadcasters transmitted their signals from the antenna.
To my knowledge, there were no studios on the 110th floor, only tv and radio equipment.

4. Most of the equipment was located in the core and on the aforementioned mechanical floors. I think there was also additional gear in the basement levels of the WTC complex.

5. The stairways went through the whole building. However not all elevators were running from ground floor to the top since this would have taken up too much space. That's the reason express elevators were introduced, which brought you to a "Sky lobby" (44th and 78th floor) where you could switch to a local elevator. There was an express elevator that went from the lobby up to the 107th floor. Apparently not all floors were accessible by elevators though. For instance, the 43rd floor (which was between the mechanical floors and the Sky lobby on 44th) could be only entered by escalators and the emergency stairways.

6. The floors were made out of concrete, however they had no structural role. The concrete slabs were 4 inches (10 cm) thick. The main support came from the trusses, which connected the core with the exterior columns.
Schematic of the truss system: http://www.john-knapton.com/WTC14.JPG

7. Asbestos was used in the early construction of 1 WTC (the North Tower). The building was covered with this material up to the 40th floor. But due to public concerns, the use of asbestos was stopped and it was replaced with another spray on material. As far as I know, there was no asbestos used in 2 WTC (the South Tower).

8. I don't know much about the security at the WTC. Only thing I know is, that security was increased in the aftermath of the 1993 bombing.

9. The lobby was open 24/7. The outdoor observation deck could be closed due to bad weather conditions, such as storms. This was the case on 9/10/01 for example.

10. I think, the WTC complex was supplied with power coming from a Con Ed substation which was later beneath WTC 7. I don't think that there was any back up generator, otherwise the towers would have shined during the 1977 blackout.
The WTC during the '77 blackout: https://s-media-cache-ak0.pinimg.com...7176dd0823.jpg

11. 140 feet (around 43 m)

12. They probably didn't. In most of the pictures that were either captured on the 4th of July or on New Year's Eve, the "explosions" from the fireworks were below the roofs of the towers.

13. Initially, I think there was no such insurance since almost not a single person could have imagined such an attack. I don't know much about most of the tenants. Cantor Fitzgerald however, a company that had its offices on the 101st-105th floors on the North Tower actually spent over $180 million on aid for the families that lost their loved ones on 9/11.

Last edited by TheAngrySlav; June 13th, 2017 at 09:03 PM.
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Old June 12th, 2017, 07:49 PM   #3
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To add to number 6 above, the floors were indeed "reinforced". The reinforcement consisted of two layers of .230" diameter welded wire fabric made from 70,000 to 90,000 psi yield strength steel rod. The mesh used a 4" x 10" pattern with welds at each overlap of the rods. Basically chicken wire.



As far as security, much like modern office buildings today, you had a badge that had your name and picture on it. This badge got you into the buildings, onto the elevators, and would also allow you to access your floor. My badge gave me 24 hour access to the building, but I could only physically access floors 93-100. Most of the employees at Marsh did not have 24 hour access; myself and the rest of IT did, because there were times when we'd have to go in and do maintenance in the datacenter after hours, or were on call. On more than one occasion, I had to be there all night and did not sleep until the next morning.

I miss those early morning sunrises from the top of the WTC.

Last edited by Chapelo; June 12th, 2017 at 07:56 PM.
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Old June 13th, 2017, 10:00 AM   #4
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Wow, thank you for going to the trouble to answer all those questions, I really appreciate it. That blackout picture is a little eerie!!

Chapelo, thank you for the extra info on the concrete flooring. But I'm still a bit confused. There was a post of yours I read where you had said that on a stormy day, there was enough movement in your area that people actually got motion sickness. In my head, I picture that as the entire steel structure flexing through a very slight twisting or bending motion. Either way, there would have to be something acting as a damper or shock absorber to keep that movement from transferring to the walls or floor and causing stress cracks, wouldn't there?

Again, thank you both for taking the time to share your knowledge with me.

And Chapelo, I think a good way to think about the towers is to try not to mourn that they are gone, but to celebrate the fact that they existed, and you got to be a part of their existence, and a part of their legacy. I know, easier said than done.
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Old June 13th, 2017, 06:23 PM   #5
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Hello, yes there were viscoelastic dampers at the truss seats at the exterior wall. They did seem to be pretty effective, as there was virtually no building sway felt at low speed winds. But the buildings were designed to move somewhat in wind; too stiff a structure would ultimately cause structural failure due to stresses and shearing forces.

I feel very fortunate to have experienced the buildings as they were. I try not to focus too much on 9/11 these days, I've done my grieving and healing.
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Old June 13th, 2017, 10:29 PM   #6
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One more thing about the floors. Certain floors in the towers were framed differently from the typical office floors.

The mechanical floors, and floors near mechanical levels were framed in beams, rather than trusses. This included floors 7-8, 41-42, 43, 75-77, and 107-110.

This image is from the 106th floor of 1WTC and was taken in 1978; you can see the beams supporting the 107th floor.

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Old June 15th, 2017, 01:09 PM   #7
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Quote:
Originally Posted by Chapelo View Post
One more thing about the floors. Certain floors in the towers were framed differently from the typical office floors.

The mechanical floors, and floors near mechanical levels were framed in beams, rather than trusses. This included floors 7-8, 41-42, 43, 75-77, and 107-110.
Nice observation Chapelo. Do you maybe know why there were beams instead of the common trusses? Was it maybe because the trusses were too light for the mechanical floors?

Last edited by TheAngrySlav; June 15th, 2017 at 03:22 PM.
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Old June 15th, 2017, 08:06 PM   #8
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I'm not entirely sure, but weight was probably a factor. I know the mechanical floors were double-height floors, and contained heavy equipment.

The floor slabs on those floors were thicker too, using standard weight concrete (130-150 psi), instead of the lightweight (110 psi) concrete used on the office floors.
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Old June 17th, 2017, 09:30 PM   #9
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Now I'm asking myself how the towers would have performed on 9/11 if every floor was equipped with these kind of beams instead of the lightweight trusses. The buildings would have probably collapsed, but much later.
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Old June 20th, 2017, 12:45 AM   #10
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I have a feeling they wouldn't have collapsed, but we can only speculate.

The trusses were very thin and especially prone to thermal effects, in this case, they heated to the point where the floors began to sag, pulling in the exterior walls. The truss-seat connections at the exterior walls were somewhat flimsy. Beams would have heated up slower, and would have had a much more robust connection to both the core columns and the perimeter columns.

The Sears Tower and the Standard Oil Building were built with the same floor truss system; it's possible they too would have collapsed in a similar manner.
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Old June 20th, 2017, 03:08 AM   #11
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I'm guessing if they had been built with reinforced concrete cores like modern day offices instead of steel they wouldn't have collapsed or it would have taken much longer.

Nonetheless they held up well given the circumstances.
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Old June 21st, 2017, 04:19 AM   #12
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Well, there are still steel columns in the core of the new 1WTC, but surrounded by 2-6 foot thick reinforced concrete walls.

If the originals had these reinforced cores, they would not have collapsed, since the core columns would not have been compromised by the jet impacts. There would still be a tremendous loss of life, and the perimeter columns would still be damaged/severed, but the aircraft would most likely not be able to penetrate the core of the buildings. The severed perimeter columns, as they did on 9/11, would redistribute their loads to the adjacent intact perimeter columns and spandrels, but since the core columns were not damaged in this scenario, they would still continue to bear the gravity loads as intended.

And the standpipes for the sprinkler system wouldn't have been severed, the stairways would be intact, allowing the sprinkler system to function, and providing access for firefighters to fight the fires.

But as you said, the buildings performed well. We'd be looking at an unspeakable death toll had the towers collapsed immediately.

Last edited by Chapelo; June 21st, 2017 at 04:26 AM.
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Old June 26th, 2017, 05:31 PM   #13
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Great thread. Just saw The Walk (those last few moments are very moving)

But regarding question 10) about the powering of the site.....are the 16 acres now powered by the cooling plant under the memorial?
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