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The text below is extracted from
the following link, including the red highlighted text:
http://911research.wtc7.net/mirrors/guardian2/wtc/WTC_ch2.htm
The WTC towers, also known as WTC 1 and WTC 2, were the primary components
of the seven building World Trade Center complex. Each of the towers
encompassed 110 stories above the Plaza level and seven levels below. WTC
1 (the north tower) had a roof height of 1,368 feet, briefly earning it
the title of the world's tallest building. WTC 2 (the south tower) was
nearly as tall, with a roof height of 1,362 feet. WTC 1 also supported a
360-foot-tall television and radio transmission tower. Each building had a
square floor plate, 207 feet 2 inches long on each side. Corners were
chamfered 6 feet 11 inches. Nearly an acre of floor space was provided at
each level. A rectangular service core with overall dimensions of
approximately 87 feet by 137 feet, was present at the center of each
building, housing 3 exit stairways, 99 elevators, and 16 escalators.
Note, that this description of the core is meant to
mislead the reader by directing attention away from the cores main
purpose, which was to support most of the gravity load (weight) of the
building and to reduce it to just "an entrance and exit". Both the central
core and the outer wall supported the gravity load (were load bearing).
The core provided the strength needed to support the bulk of the weight,
while the outer wall provided the necessary rigidity to resist lateral
loading due to the wind. The requirement to resist lateral loading, is the
dominant feature determining the design of tall buildings.
The project was developed by the Port Authority of
New York and New Jersey (hereafter referred to as the Port Authority), a
bi-state public agency. Original occupancy of the towers was dominated by
government agencies, including substantial occupancy by the Port Authority
itself. However, this occupancy evolved over the years and, by 2001, the
predominant occupancy of the towers was by commercial tenants, including a
number of prominent financial and insurance services firms.
Design architecture was provided by Minoru Yamasaki & Associates, and
Emery Roth & Sons served as the architect of record.
[Minoru Yamasaki died in 1986.]
Since these companies have nothing to hide, they should
provide the architectural plans of the WTC to the world, so that any
misunderstandings regarding the facts of the collapse, may be established.
In fact, Minoru Yamasaki & Associates, and Roth & Sons, or their
descendent companies, should put the entire set of architectural plans on
the internet. Skilling, Helle, Christiansen,
Robertson were the project structural engineers; Jaros, Baum & Bolles were
the mechanical engineers; and Joseph R. Loring & Associates were the
electrical engineers. The Port Authority provided design services for site
utilities, foundations, basement retaining walls, and paving. Ground
breaking for construction was on August 5, 1966. Steel construction began
in August 1968. First tenant occupancy of WTC 1 was in December 1970, and
occupancy of WTC 2 began in January 1972. Ribbon cutting was on April 4,
1973.
Structural Description
WTC 1 and WTC 2 were similar, but not identical. WTC 1 was 6 feet taller
than WTC 2 and also supported a 360-foot tall transmission tower. The
service core in WTC 1 was oriented east to west, and the service core in
WTC 2 was oriented north to south. Service core,
service core,... more propaganda. The more you are told the core is just
for servicing the building, the more you believe it. Right?
In addition to these basic configuration
differences, the presence of each building affected the wind loads on the
other, resulting in a somewhat different distribution of design wind
pressures, and, therefore, a somewhat different structural design of the
lateral-force-resisting system. In addition, tenant improvements over the
years resulted in removal of portions of floors and placement of new
private stairways between floors, in a somewhat random pattern. Figure 2-2
presents a structural framing plan representative of an upper floor in the
towers.
Figure 2-8 (above) shows the
erection of floor framing during original construction.
This is a view of one of the mechanical floors (they
were the only floors for which the prefabricated perimeter wall units were
not staggered). The mechanical floors where not supported by trusses but
by solid steel beams. Composite action between these beams and the
concrete slab was by welded shear studs. The concrete slab was apparently
considerably thicker than that of your average floor and specially
reinforced with steel beams (a stack of which are visible in the
foreground of the photo?). Such floors were necessary to enable the towers
to resist the significant lateral force of hurricane force winds.
We have the following quote from Engineering News-Record, January 1, 1970.
On the 41st and 42nd floors, both towers will house mechanical
equipment. To accommodate the heavy loads, the floors are designed as
structural steel frame slabs. All other floors from the ninth to the top
(except for 75 and 76, which will also carry mechanical equipment) have
typical truss floor joists and steel decking.
Typical office floors have 4-in. thick slabs of composite construction
using top chord knuckles of the joists (trusses), which extend into the
slab, as shear connectors. On mechanical floors, composite action is
provided by welded stud shear connectors.
The other high-rise in figure 2-8 is the Verizon building. Note the
vertical gaps in the box columns of the perimeter wall. Gaps in the box
columns do not seem to be a sensible feature in a load bearing wall.
Click here for:
World Trade Centre
engineer revisits the tragedy |
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