Burj Khalifa
The Burj Khalifa known as the Burj Dubai prior to its inauguration in 2010, is a skyscraper in Dubai, United Arab Emirates. With a total height of 829.8 m (2,722 ft, just over half a
mile) and a roof height (excluding antenna but including a 244 m spire) of 828 m
(2,717 ft), the Burj Khalifa has been the tallest structure and building in the world since its topping
out in 2009.
Development
Construction began on 6 January 2004, with the exterior of
the structure completed on 1 October 2009. The building officially opened on 4
January 2010 and is part of the 2 km2 (490-acre) Downtown
Dubai development
at the 'First Interchange' along with Sheikh
Zayed Road, near Dubai's main
business district. The tower's architecture and engineering were performed by Skidmore, Owings & Merrill of Chicago, with Adrian Smith as chief architect, and Bill Baker as a chief structural engineer. The primary
contractor was Samsung
C&T of South
Korea.
Architecture
The tower was designed by Skidmore, Owings, and Merrill (SOM),
which also designed the Willis
Tower (formerly the
Sears Tower) in Chicago and the One World Trade Center in New
York City. Burj Khalifa uses
the bundled tube design of the Willis
Tower, invented by Fazlur Rahman Khan. Due to its tubular system, proportionally only half
the amount of steel was used in the construction, compared to the Empire State Building. Khan's contributions to the design of tall
buildings have had a profound impact on architecture and engineering. It would
be difficult to find any worldwide practices in the design of tall buildings
that have not been directly or indirectly influenced by his work. The
design is reminiscent of Frank Lloyd Wright's vision for The
Illinois, a mile-high
skyscraper designed for Chicago, as well as Chicago's Lake
Point Tower. When Adrian Smith was conceiving the project at SOM, he looked out his
office window toward Lake Point Tower's curved three wing layout, "There's
the prototype", he said. According to Strabala, Burj Khalifa
was designed based on the 73 floors Tower Palace Three, an all-residential building in Seoul. In its early planning, Burj Khalifa was intended to be
entirely residential
Construction
The tower was constructed by Samsung C&T from South Korea, which also did work on the Petronas Twin Towers and Taipei 101. Samsung C&T built the
tower in a joint venture with BESIX from Belgium
and Arabtec from the UAE. Turner was
the project manager on the main construction contract. Hong Kong-based Far East Aluminum combined to provide the
exterior cladding for Burj Khalifa.
The contractor and the
engineer of record were Hyder Consulting. Under UAE law, the
contractor and the engineer of record is jointly and severally
liable for the performance of Burj Khalifa.
The primary structure is reinforced concrete. Putzmeister created a new, super high-pressure trailer concrete pump, the BSA 14000 SHP-D, for this project. Burj Khalifa's construction used 330,000 m3 (431,600 cu yd) of concrete and 55,000 tonnes (61,000 short tons; 54,000 long tons) of steel rebar and construction took 22 million man-hours. In May 2008 Putzmeister pumped concrete with more than 21 MPA ultimate compressive strength of gravel to surpass the 600 meters weight of the effective area of each column from the foundation to the next fourth level, and the rest was by metal columns jacketed or covered with concrete to a then-world
In 2003, 33 test holes were
drilled to study the strength of the bedrock underlying the structure. "Weak
to very weak sandstone and siltstone" was found, just meters
below the surface. Samples were taken from test holes drilled to a depth of 140
meters, finding weak to very weak rock all the way. The study described
the site as part of a "seismically active area". Another
challenging element was the shamal which often creates sandstorms.
Over 45,000 m3 (58,900 cu yd)
of concrete, weighing more than 110,000 tonnes (120,000 short tons; 110,000 long tons) were used to construct the concrete
and steel foundation, which features 192 piles; each pile is 1.5 meter in
diameter by 43 m in length, buried more than 50 m (164 ft) deep. The
foundation was designed to support the total building weight of approximately
450,000 tonnes (500,000 short tons; 440,000 long tons). This weight was then divided by
the compressive strength of concrete of which is 30 MPa which yielded a 450
sq.meters of vertical normal effective area, which then yielded to a 12 meters
by 12 meters dimensions. A cathodic protection system
is under the concrete to neutralize the sulfate and chloride-rich groundwater
and prevent corrosion.
The Burj Khalifa is highly
compartmentalized. Pressurized, air-conditioned refuge floors are located every
13 floors (in floors G, 13, 26, 39, 52, etc.) where people can shelter on their
long walk down to safety in case of an emergency or fire.
Special mixes of concrete
were made to withstand the extreme pressures of the massive building weight; as
is typical with reinforced concrete construction, each batch of concrete was
tested to ensure it could withstand certain pressures. CTLGroup, working for Skidmore, Owings and
Merrill conducted the creep and shrinkage testing critical for the structural
analysis of the building.
The consistency of the
concrete used in the project was essential. It was difficult to create a
concrete that could withstand both the thousands of tonnes bearing down on it
and the Persian Gulf temperatures
that can reach 50 °C (122 °F). To combat this problem, the concrete
was not poured during the day. Instead, during the summer months, ice was added
to the mixture and it was poured at night when the air was cooler and the
humidity was higher. Cooler concrete cures more evenly and is, therefore, less
likely to set too quickly and crack. Any significant cracks could have put the
entire project in jeopardy.
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