2. The World Trade Center is a complex of buildings
under construction in Lower Manhattan , New York
City , United States, replacing an earlier complex of
seven buildings with the same name on the same
site. The original World Trade Center featured
landmark twin towers, which opened on April 4,
1973, and were destroyed in the September 11
attacks of 2001, along with 7 World Trade Center.
The other buildings in the complex were severely
damaged by the collapse of the twin towers
4. The site is being rebuilt with six new
skyscrapers, a memorial to those killed in
the attacks, and a transportation hub. One
world trade center will be the lead building
for the new complex, reaching more than
100 stories at its completion. It is the tallest
building in the United States.
5. At the time of their completion the "Twin Towers", the
original 1 WTC (417 m), and 2 TWC were the tallest
building in the world. The other buildings in the complex
included the 3 WTC, 4 WTC, 5 WTC, 6 WTC, and 7
WTC. All of these buildings were built between 1975 and
1985, with a construction cost of $400 million
($2,300,000,000 in 2014 dollars).The complex was
located in New York City's Financial District and contained
13,400,000 square feet (1,240,000 m2) of office space.
6. On the morning of September 11, 2001, Al-Qaeda-affiliated
hijackers flew two Boeing 767 jets into the
complex, one into each tower, in a coordinated act
of terrorism. After burning for 56 minutes, the South
Tower (2) collapsed, followed a half-hour later by the
North Tower (1). The attacks on the World Trade
Center killed 2,753 people.Falling debris from the
towers, combined with fires that the debris initiated
in several surrounding buildings, led to the partial or
complete collapse of all the other buildings in the
complex and caused catastrophic damage to ten
other large structures in the surrounding area
(including the World Financial Center). The process
of cleaning up and recovery at the World Trade
Center site took eight months.
7. Over the following years, plans were created for
the reconstruction of the World Trade Center.
The Lower Manhattan Development
Corporation (LMDC), established in November
2001 to oversee the rebuilding process, organized
competitions to select a site plan and memorial
design. Memory Foundations, designed by Daniel
Libeskind, was selected as the master plan;
however, substantial changes were made to the
design.
8. The first new building at the site was the 7 World Trade Center,
which opened in May 2006. The memorial section of the National
September 11 Memorial & Museum opened on September 11,
2011 and the museum opened in May 2014. Construction of
the One World Trade Center is open in 2013; the 4 World Trade
Center opened on November 13, 2013; the 3 World Trade
Center is under construction and expected to open in 2016, 5
World Trade Center will be developed by the Port Authority of New
York and New Jersey, but, as of February 2014, a schedule was
not confirmed. Two World Trade Center's is still expected to be
completed before 2020.
9. ORIGINAL BUILDING
Minoru Yamasaki as lead architect has a
plan for the towers to be 80 stories
tall, but to meet the Port Authority's
requirement for 10,000,000 square feet
(930,000 m2) of office space, the buildings
would each have to be 110 stories tall. A
major limiting factor in building height is
the issue of elevators; the taller the
building, the more elevators are needed to
service the building, requiring more
space-consuming elevator
banks.Yamasaki and the engineers
decided to use a new system with two "sky
lobbies”
10. Construction started 1 WTC: August 1968
2 WTC: January 1969
3 WTC: December 1979
4, 5, and 6 WTC: 1970
7 WTC: 1983
Completed 1 WTC: December 23, 1970
2 WTC: July 19, 1971
3 WTC: July 1981
4, 5, and 6 WTC: 1975
7 WTC: May 1987
Opening April 4, 1973
Floor count 1 and 2 WTC: 110 floors
3 WTC: 22 floors
4 and 5 WTC: 9 floors
6 WTC: 8 floors
7 WTC: 47 floors
11. The structural engineering firm Worthington, Skilling, Helle
& Jackson worked to implement Yamasaki's design,
developing thetube-frame structural system used in the
twin towers. The tube frame design, using steel core and
perimeter columns protected with sprayed-on fire resistant
material, created a relatively lightweight structure that
would sway more in response to the wind compared to
traditional structures .The tube-frame design, earlier
introduced by Fazlur Khan, was a new approach that
allowed more open floor plans than the traditional design
that distributed columns throughout the interior to support
building loads.
12. The World Trade Center towers used high-strength, load-bearing
perimeter steel columns called Vierendeel
trusses that were spaced closely together to form a
strong, rigid wall structure, supporting virtually all lateral
loads such as wind loads, and sharing the gravity load
with the core columns.
The core of the towers housed the elevator and utility
shafts, restrooms, three stairwells, and other support
spaces. The core of each tower was a rectangular area
and contained 47 steel columns running from the bedrock
to the top of the tower. The floors used prefabricated floor
trusses ,supported their own weight as well as live loads,
providing stability to the walls and distributing wind loads
among the walls.The floors consisted of 4 inches (10 cm)
thick lightweight concrete slabs.
13. When World Trade Center twin towers were completed,
the total costs had reached $900 million.The ribbon
cutting ceremony was on April 4, 1973
14. NEW BUILDING
The new complex includes One World Trade
Center (formerly known as the Freedom Tower), 7 World
Trade Center, three other high-rise office buildings, a
museum and memorial, and a transportation hub.
The process of cleanup and recovery continued 24 hours
a day over a period of eight months. On May 30, 2002, a
ceremony was held to officially mark the end of the
cleanup efforts
