The Letter
The Wizard of Oz
architect of some stature in his community. He has never let his successes go to
his head, and is still the nice guy I grew up with.
Just a day or two ago, my parents got a letter from him regarding the recent
national tragedy in New York and Washington DC. He gave some technical details
about the construction methods used in the WTC Towers which are very
interesting, and also talks about his own thoughts on effects of the destruction
on the country and himself. I found it extremely interesting, even if he is my
brother, and, with his permission, will post it here in the NG for you to read
if you care to. The technical aspects of the constructions get a little
detailed, but he wrote it aiming at our parents who are non- professional in his
field, but learned a little from him when he was in school.
His own thoughts are interesting, to me, but I may be just prejudiced. Read it
if you wish, or just move on to the next one.
--
Regards,
Wiz
Reply to: wizard (at) wiz dot mailshell dot com
Complaints to: ab...@wiz.mailshell.com
The Wizard of Oz
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September 17, 2001
Dear Mom and Dad,
I had just started a letter to you folks when I checked my voice mail
and had a message from Dad to call him back. I enjoyed our brief call, and
thanks for the stock update. I am still shaken over what has happened. I keep
replaying that day over and over in my head. We studied the Trade Towers
extensively when I was in school. They were one of the first examples of an
innovative and efficient structural concept called "tube" restraint. The Sears
Towers are a variation called "bundled tube construction" and the idea is based
on a minimum of interior columns, with the exterior facade having more numerous
exterior perimeter columns. In the case of the WTC, there are no interior
columns. Only a central concrete core roughly 60-80 feet square comprised of
several vertical voids that house exit stairs, hoistways for the elevators,
utility raceways and mechanical chases; and also, significantly, the sprinkler
system main lines. The floors were prefabricated broad cellular panels of
parallel trusses and main decking that had a light weight concrete topping
applied after they were installed. They spanned a distance of roughly 60 feet
from the concrete core to the exterior gridwork of columns and horizontal
beams. the floor trusses restrained the exterior walls and prevented them from
buckling outward. The exterior structural system was prefabricated in panels of
multiple columns (steel tubes only 14 inches square) that spanned vertically
through 2 or three floors. This was a fast way to erect the building and helped
enclose the building faster. At the upper floors, the winds are so high at
times that no other work can begin (including pouring the floor topping) until
the exterior is in place.
Once the building was closed in, the underside of the floor assemblies
were sprayed with a cementitious mineral fiber coating for fire resistance.
Then the sprinkler lines were run, along with ductwork laterals from the main
ducts built into the floor assemblies. A ceiling grid would have been hung and
minor interior partitions fastened to the floor and ceiling grid and covered
with gypsum board panels. A building that size, 10 million square feet, would
have each floor (roughly 40,000 square feet each) separated by fire/smoke
barriers and exit corridors that prevented the migration of smoke and fire
throughout a given floor.
The stairs would have been considered an absolutely safe haven to leave
a fire-envolved floor to an area of safety. In high rise construction, the
stair towers are required to have the capability of being pressurized by large
fans so that, in a fire emergency, smoke will be kept out of the stair; even
with a number of the stair doors open. Otherwise it makes a perfect chimney.
That is why you should never use an elevator in a fire. There are hose
connections and hose cabinets at each floor so the firemen can fight the blaze
where ever it may occur without hauling hose up the building.
I'm no structural engineer, but the impact of the planes must have
severely damaged the center core. They were designed to handle a Boeing 707; a
typical plane in use in the late 60's. But no one imagined the thousands of
gallons of fuel that poured into the structure. With essentially every fire
barrier breached, the fuel must have flowed everywhere, and poured down the
cavities between floors. They say the fuel combined with all of the furnishings
produced fire temperatures in excess of 1000 degrees. Building beams and
columns are protected with the fire proofing to prevent structural failure at
temperatures of 1500 degrees for 1-hour. That is the way we design them per the
requirements of the various building codes. Combined with the automatic
sprinkler systems, the fire proofing in a structural steel building is intended
to give firemen enough time to contain the blaze.
With the sprinkler risers severed, and the cascading flood of fuel, the
firemen would never have been able to save the building's structure from
thermal failure in time. Ironically, Building 2 survived exactly one hour
before it collapsed. Building 1 lasted close to 1 3/4 hours. When the high
temperature caused the first few floor trusses to sag and pull away from the
exterior wall, the wall buckled outwards, causing a chain reaction of dropping
floor trusses, and buckling walls all the way to the bottom. The center core
would have been only designed to accommodate gravity loads, vertically imposed
loads. The falling floors must have created so much lateral force that the core
disintegrated in the same chain reaction. As each floor pancaked, a shockwave
blew out the windows and expelled the dust cloud of pulverized concrete, gypsum
dust, and the cementitious fiber fireproofing. It was one of the first
buildings constructed without asbestos fireproofing, so there should have been
no danger of that in the dust cloud.
In the last week, I have moved from shock and disbelief, through grief,
and have settled into an anger that won't go away. I keep thinking of those now
5,400 innocent people looking themselves in the mirror for the last time,
getting dressed for the last time and going to work. I can't imagine how those
firemen searching through the debris must feel. People of my generation, as I
mentioned to you before, never had a Great Depression, or a Pearl Harbor to
galvanize us and crystallize our beliefs; to bring us together as one nation. We
were just a pampered, unappreciative, self-centered bunch of self important
egos; wondering how best to get ahead. I don't think that is the case any more.
I still don't think the seriousness and gravity of this tragedy has hit us;
those of us without your WW II perspective.
September 18, 2001
I saw David Letterman last night; his first broadcast since Tuesday. He
will probably never have a re-run of it, and if you didn't see it, it would be
hard to describe. Last week I wondered how his show and Leno's would be able to
come back with their usual irreverent "make-fun-of-everything-that-moves" brand
of humor. Letterman's show opened with no music or monologue. Just him sitting
at his desk with scattered quiet applause. He said that he didn't now if this
show would work, doubting whether he could pull it off. Then he proceeded to
convey his thoughts for about twenty minutes. His hands were shaking and his
voice wavered. He lavished Giuliani with praise, saying he was "the definition
of courage..." He used profanity, un-edited but somehow appropriate. It was
riveting. His first guest was Dan Rather, who has always seemed to me too cool
and professional to the point of being dull. Well he made it clear by the way
he spoke and the things he said, that he had been waiting a long time to unload
his thoughts and speak his mind. He broke down twice; too emotional to finish
what he was saying. It was an incredible sight.
I don't know what is going to happen next. Does anybody? I can't
believe how astonishingly unbelievable this all has been. I think I know now
how you all might have felt on December 7th. But look where we are 60 years
later. I'm glad we have the experienced folks in there. Cheny, Powell,
Rumsfeld. And the young frat boy Bush doesn't seem that way any more. He has
really risen to the horrible occasion. I can't bring myself to think what Gore,
Reno, and Albright would do to muster confidence in the country. I know we'll
get through this. Those buildings will be built back like they were, only
taller. And we'll leave your grandchildren a safer world. God bless America.
You folks take care.
Love, Phil