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Burj Khalifa (برج خليفة "Khalifa Tower"), known as Burj Dubai prior to its inauguration, is a skyscraper in Dubai, United Arab Emirates, and is currently the tallest man-made structure ever built, at 828 m. Construction began on 21 September 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 new 2 km2 flagship development called Downtown Dubai at the 'First Interchange' along 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 (now at his own firm) as chief architect, and Bill Baker as chief structural engineer. The primary contractor was Samsung C&T of South Korea.

The total cost for the project was about US $1.5 billion; and for the entire "Downtown Dubai" development, US $20 billion. In March 2009, Mohamed Ali Alabbar, chairman of the project's developer, Emaar Properties, said office space pricing at Burj Khalifa reached US $4,000 per sq ft (over US $43,000 per m2) and the Armani Residences, also in Burj Khalifa, sold for US $3,500 per sq ft (over US $37,500 per m2).

The project's completion coincided with the global financial crisis of 2007–2010, and with vast overbuilding in the country, led to high vacancies and foreclosures. With Dubai mired in debt from its huge ambitions, the government was forced to seek multibillion dollar bailouts from its oil rich neighbor Abu Dhabi. Subsequently, in a surprise move at its opening ceremony, the tower was renamed Burj Khalifa, said to honour the UAE President Khalifa bin Zayed Al Nahyan for his crucial support.

Due to the slumping demand in Dubai's property market, the rents in the Burj Khalifa plummeted 40% some ten months after its opening. Out of 900 apartments in the tower around 825 were still empty at that time.

Conception
Burj Khalifa has been designed to be the centrepiece of a large-scale, mixed-use development that would include 30,000 homes, nine hotels such as The Address Downtown Dubai, 3 ha of parkland, at least 19 residential towers, the Dubai Mall, and the 12 ha man-made Burj Khalifa Lake.

The building has returned the location of Earth's tallest freestanding structure to the Middle East where the Great Pyramid of Giza claimed this achievement for almost four millennia before being surpassed in 1311 by Lincoln Cathedral in England.

The decision to build Burj Khalifa is reportedly based on the government's decision to diversify from an oil based economy to one that is service and tourism oriented. According to officials, it is necessary for projects like Burj Khalifa to be built in the city to garner more international recognition, and hence investment. "He (Sheikh Mohammed bin Rashid Al Maktoum) wanted to put Dubai on the map with something really sensational," said Jacqui Josephson, a tourism and VIP delegations executive at Nakheel Properties.

Current records

 * Tallest skyscraper to top of spire: 828 m (previously Taipei 101 – 509.2 m)


 * Tallest structure ever built: 828 m (previously Warsaw radio mast – 646.38 m)
 * Tallest extant structure: 828 m (previously KVLY-TV mast – 628.8 m)
 * Tallest freestanding structure: 828 m (previously CN Tower – 553.3 m)
 * Building with most floors: 160 (previously Willis Tower – 108)
 * Building with highest occupied floor in the world: 160th floor
 * World's highest elevator installation, situated inside a rod at the very top of the building
 * World's fastest elevators at speed of 64 km/h or 18 m/s (previously Taipei 101 – 16.83 m/s)
 * Highest vertical concrete pumping (for a building): 606 m (previously Taipei 101 – 449.2 m)
 * The first world's tallest structure in history to include residential space
 * Highest outdoor observation deck in the world (124th floor) at 452 m
 * World's highest mosque (located on the 158th floor)
 * World's highest installation of an aluminium and glass facade, at a height of 512 m
 * World's highest swimming pool (76th floor)
 * World's highest nightclub (144th floor).
 * World's highest restaurant called At.mosphere located on 122nd floor at the height of 442 m. (Previously the world’s highest restaurant was 360, at a height of 350 m in CN Tower).
 * World's highest New Year fireworks display.

History of height increases
There are unconfirmed reports of several planned height increases since its inception. Originally proposed as a virtual clone of the 560 m Grollo Tower proposal for Melbourne, Australia's Docklands waterfront development, the tower was redesigned by Skidmore, Owings & Merrill (SOM). Marshall Strabala, an SOM architect who worked on the project until 2006, late 2008 said that Burj Khalifa was designed to be 808 m tall.

The design architect, Adrian Smith, felt that the uppermost section of the building did not culminate elegantly with the rest of the structure, so he sought and received approval to increase it to the current height. It has been explicitly stated that this change did not include any added floors, which is fitting with Smith's attempts to make the crown more slender.

Delay
Emaar Properties announced on 9 June 2008 that construction of Burj Khalifa was delayed by upgraded finishes and would be completed only in September 2009. An Emaar spokesperson said "The luxury finishes that were decided on in 2004, when the tower was initially conceptualized, is now being replaced by upgraded finishes. The design of the apartments has also been enhanced to make them more aesthetically attractive and functionally superior." A revised completion date of 2 December 2009 was then announced. However, Burj Khalifa was opened on 4 January 2010.

Architecture and design
The tower is designed by Skidmore, Owings & Merrill, which also designed the Willis Tower (formerly the Sears Tower) in Chicago and the new One World Trade Center in New York City among numerous other famous high-rises. The building resembles the bundled tube form of the Willis Tower, but is not a bundle tube structure. Its design is reminiscent of Frank Lloyd Wright's vision for The Illinois, a mile high skyscraper designed for Chicago. According to Marshall Strabala, an SOM architect who worked on the building's design team, Burj Khalifa was designed based on the 73 floor Tower Palace Three, an all residential building in Seoul. In its early planning, Burj Khalifa was intended to be entirely residential.

Subsequent to the original design by Skidmore, Owings & Merrill, Emaar Properties chose Hyder Consulting to be the supervising engineer. Hyder was selected for its expertise in structural and MEP (mechanical, electrical and plumbing) engineering. Hyder Consulting's role was to supervise construction, certify SOM's design, and be the engineer and architect of record to the UAE authorities. Emaar Properties also engaged GHD, an international multidisciplinary consulting firm, to act as an independent verification and testing authority for concrete and steelwork.

The design of Burj Khalifa is derived from patterning systems embodied in Islamic architecture. According to the structural engineer, Bill Baker of SOM, the building's design incorporates cultural and historical elements particular to the region. The Y-shaped plan is ideal for residential and hotel usage, with the wings allowing maximum outward views and inward natural light. The design architect, Adrian Smith, has said the triple lobed footprint of the building was inspired by the flower Hymenocallis. The tower is composed of three elements arranged around a central core. As the tower rises from the flat desert base, setbacks occur at each element in an upward spiralling pattern, decreasing the cross section of the tower as it reaches toward the sky. There are 27 terraces in Burj Khalifa. At the top, the central core emerges and is sculpted to form a finishing spire. A Y-shaped floor plan maximizes views of the Persian Gulf. Viewed from above or from the base, the form also evokes the onion domes of Islamic architecture. During the design process, engineers rotated the building 120 degrees from its original layout to reduce stress from prevailing winds. At its tallest point, the tower sways a total of 1.5 m.

To support the unprecedented height of the building, the engineers developed a new structural system called the buttressed core, which consists of a hexagonal core reinforced by three buttresses that form the ‘Y' shape. This structural system enables the building to support itself laterally and keeps it from twisting.

The spire of Burj Khalifa is composed of more than 4000 t of structural steel. The central pinnacle pipe weighing 350 t was constructed from inside the building and jacked to its full height of over 200 m using a strand jack system. The spire also houses communications equipment.

More than 1,000 pieces of art will adorn the interiors of Burj Khalifa, while the residential lobby of Burj Khalifa will display the work of Jaume Plensa, featuring 196 bronze and brass alloy cymbals representing the 196 countries of the world. The visitors in this lobby will be able to hear a distinct timbre as the cymbals, plated with 18-carat gold, are struck by dripping water, intended to mimic the sound of water falling on leaves.

The exterior cladding of Burj Khalifa consists of 142000 m2 of reflective glazing, and aluminium and textured stainless steel spandrel panels with vertical tubular fins. The cladding system is designed to withstand Dubai's extreme summer temperatures.

Additionally, the exterior temperature at the top of the building is thought to be 6°C (11°F) cooler than at its base. Over 26,000 glass panels were used in the exterior cladding of Burj Khalifa. Over 300 cladding specialists from China were brought in for the cladding work on the tower.

A 304 room Armani Hotel, the first of four by Armani, occupies 15 of the lower 39 floors. The hotel was supposed to open on 18 March 2010 but after several delays the hotel finally opened the public on 27 April 2010. The corporate suites and offices were also supposed to open from March onwards but the hotel and observation deck remain the only parts of the building which are open.

The sky lobbies on the 43rd and 76th floors will house swimming pools. Floors through to 108 will have 900 private residential apartments (which, according to the developer, sold out within eight hours of being on the market). An outdoor zero-entry swimming pool will be located on the 76th floor of the tower. Corporate offices and suites fill most of the remaining floors, except for a 122nd, 123rd and 124th floor where the At.mosphere restaurant, sky lobby and an indoor and outdoor observation deck is located respectively. Burj Khalifa will receive its first residents from February 2010. They will be among the first of 25,000 people who will live there.

Burj Khalifa is expected to hold up to 35,000 people at any one time. A total of 57 elevators and 8 escalators are installed. The elevators have a capacity of 12 to 14 people per cabin, the fastest rising and descending at up to 18 m/s. Engineers had considered installing the world's first triple-deck elevators, but the final design calls for double-deck elevators. The double-deck elevators are equipped with entertainment features such as LCD displays to serve visitors during their travel to the observation deck. The building has 2,909 stairs from the ground floor to the 160th floor.

The graphic design identity work for Burj Khalifa is the responsibility of Brash Brands, who are based in Dubai. Design of the global launch events, communications, and visitors centers for Burj Khalifa have also been created by Brash Brands as well as the roadshow exhibition for the Armani Residences, which are part of the Armani Hotel within Burj Khalifa, which toured Milan, London, Jeddah, Moscow and Delhi.

Water supply system
The Burj Khalifa's water system supplies an average of 946000 l of water per day.

At the peak cooling times, the tower requires cooling equivalent to that provided by 10000 t of melting ice in one day. The building has a condensate collection system, which uses the hot and humid outside air, combined with the cooling requirements of the building and results in a significant amount of condensation of moisture from the air. The condensed water is collected and drained into a holding tank located in the basement car park, this water is then pumped into the site irrigation system for use on the Burj Khalifa park.

Maintenance
To wash the 24,348 windows, a horizontal track has been installed on the exterior of Burj Khalifa at levels 40, 73 and 109. Each track holds a 1500 kg bucket machine which moves horizontally and then vertically using heavy cables. Above level 109, up to tier 27 traditional cradles from davits are used. The top of the spire, however, is reserved for specialist window cleaners, who brave the heights and high winds dangling by ropes to clean and inspect the top of the pinnacle. Under normal conditions, when all building maintenance units will be operational, it will take 36 workers three to four months to clean the entire exterior facade.

Unmanned machines will clean the top 27 additional tiers and the glass spire. The cleaning system was developed in Melbourne, Australia at a cost of A$8 million.

The Dubai Fountain
Outside, and at a cost of Dh 800 million (US$217 million), a record setting fountain system was designed by WET Design, the California based company responsible for the fountains at the Bellagio Hotel Lake in Las Vegas. Illuminated by 6,600 lights and 50 coloured projectors, it is 275 m long and shoots water 150 m into the air, accompanied by a range of classical to contemporary Arabic and world music. On 26 October 2008 Emaar announced that based on results of a naming contest the fountain would be called the Dubai Fountain.

Observation deck
An outdoor observation deck, named At the Top, opened on 5 January 2010 on the 124th floor. It is the second highest observation deck in the world and the highest outdoor observation deck in the world, at 452 m. The observation deck also features the Behold Telescope, an augmented reality device developed by gsmprjct° of Montréal, which allows visitors to view the surrounding landscape in real-time, and to view previously saved images such as those taken at different times of day or under different weather conditions. To manage the daily rush of sightseers, visitors are able to purchase tickets in advance for a specific date and time and at a 75% discount over tickets purchased on the spot.

On 8 February 2010, the observation deck was closed to the public after power supply problems caused an elevator to become stuck between floors, trapping a group of tourists for 45 minutes. Despite rumours of the observation deck reopening for St. Valentines Day (14 February), it remained closed until 4 April 2010.

Burj Khalifa park
Burj Khalifa is surrounded by an 11 ha park designed by landscape architects SWA Group. The design of the park is also inspired by the core design concepts of Burj Khalifa which is based on the symmetries of the desert flower, Hymenocallis. The park has six water features, gardens, palm lined walkways, and flowering trees. At the centre of the park and the base of Burj Khalifa is the water room, which is a series of pools and water jet fountains. In addition the railing, benches and signs incorporate images of Burj Khalifa and the Hymenocallis flower.

The plants and the shrubbery will be watered by the buildings's condensation collection system that uses water from the cooling system. The system will provide 68000000 L annually. WET designers, who also developed the Dubai Fountain, developed the park's six water features.

Floor plans
The following is a breakdown of floors.

Construction
The tower was constructed by South Korean company, Samsung Engineering & Construction, which also did work on the Petronas Twin Towers and Taipei 101. Samsung Engineering & Construction built the tower in a joint venture with Besix from Belgium and Arabtec from UAE. Turner is the Project Manager on the main construction contract.

Under UAE law, the Contractor and the Engineer of Record, Hyder Consulting, is jointly and severally liable for the performance of Burj Khalifa.

The primary structural system of Burj Khalifa is reinforced concrete. Over 45000 m3 of concrete, weighing more than 110000 t were used to construct the concrete and steel foundation, which features 192 piles, with each pile is 1.5 metre diameter x 43 metre long buried more than 50 m deep. Burj Khalifa's construction used 330000 m3 of concrete and 55,000 tonnes of steel rebar, and construction took 22 million man-hours. A high density, low permeability concrete was used in the foundations of Burj Khalifa. A cathodic protection system under the mat is used to minimize any detrimental effects from corrosive chemicals in local ground water. In May 2008 concrete was pumped to a then world record delivery height of 606 m, the 156th floor. The remaining structure above is built of lighter steel.

Burj Khalifa is highly compartmentalised. Pressurized, air-conditioned refuge floors are located approximately every 35 floors where people can shelter on their long walk down to safety in case of an emergency or fire.

Special mixes of concrete are made to withstand the extreme pressures of the massive building weight; as is typical with reinforced concrete construction, each batch of concrete used was tested to ensure it could withstand certain pressures. CTLGroup, working for SOM, 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 Persian Gulf temperatures that can reach 50 C. 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 is cooler and the humidity is higher. A cooler concrete mixture cures evenly throughout and is therefore less likely to set too quickly and crack. Any significant cracks could have put the entire project in jeopardy.

The unique design and engineering challenges of building Burj Khalifa have been featured in a number of television documentaries, including the Big, Bigger, Biggest series on the National Geographic and Five channels, and the Mega Builders series on the Discovery Channel.

Milestones

 * January 2004: Excavation commences.
 * February 2004: Piling starts.
 * 21 September 2004: Emaar contractors begin construction.
 * March 2005: Structure of Burj Khalifa starts rising.
 * June 2006: Level 50 is reached.
 * February 2007: Surpasses the Sears Tower as the building with the most floors.
 * 13 May 2007: Sets record for vertical concrete pumping on any building at 452 m, surpassing the 449.2 m to which concrete was pumped during the construction of Taipei 101, while Burj Khalifa reached 130 floor.
 * 21 July 2007: Surpasses Taipei 101, whose height of 509.2 m made it the world's tallest building, and level 141 reached.
 * 12 August 2007: Surpasses the Sears Tower antenna, which stands 527.3 m.
 * 12 September 2007: At 555.3 m, becomes the world's tallest freestanding structure, surpassing the CN Tower in Toronto, and level 150 reached.
 * 7 April 2008: At 629 m, surpasses the KVLY-TV Mast to become the tallest man-made structure, level 160 reached.
 * 17 June 2008: Emaar announces that Burj Khalifa's height is over 636 m and that its final height will not be given until it is completed in September 2009.
 * 1 September 2008: Height tops 688 m, making it the tallest man-made structure ever built, surpassing the previous record-holder, the Warsaw Radio Mast in Konstantynów, Poland.
 * 17 January 2009: Topped out at 828 m.
 * 1 October 2009: Emaar announces that the exterior of the building is completed.
 * 4 January 2010: Burj Khalifa's official launch ceremony is held and Burj Khalifa is opened. Burj Dubai renamed Burj Khalifa in honour of the current President of the UAE and ruler of Abu Dhabi, Sheikh Khalifa bin Zayed al Nahyan.

Official launch ceremony
thumb|right|upright|The opening ceremony of Burj Khalifa The opening of Burj Khalifa was held on 4 January 2010. The ceremony featured a display of 10,000 fireworks, light beams projected on and around the tower, and further sound, light and water effects. The celebratory lighting was designed by UK lighting designers Speirs and Major. Using the 868 powerful stroboscope lights that are integrated into the facade and spire of the tower, different lighting sequences were choreographed, together with more than 50 different combinations of the other effects.

The event began with a short film which depicted the story of Dubai and the evolution of Burj Khalifa. The displays of sound, light, water and fireworks followed. The portion of the show consisting of the various pyrotechnic, lighting, water and sound effects was divided into three. The first part was primarily a light and sound show, which took as its theme the link between desert flowers and the new tower, and was co-ordinated with the Dubai Fountain and pyrotechnics. The second portion, called 'Heart Beat', represented the construction of the tower in a dynamic light show with the help of 300 projectors which generated a shadow-like image of the tower. In the third act, sky tracers and space cannons enveloped the tower in a halo of white light, which expanded as the lighting rig on the spire activated.

The ceremony was relayed live on a giant screen on Burj Park Island, as well as several television screens placed across the Downtown Dubai development. Hundreds of media outlets from around the world reported live from the scene. In addition to the media presence, 6,000 guests were expected.

Awards
In June 2010, Burj Khalifa was the recipient of the 2010 Best Tall Building Middle East & Africa award by the Council on Tall Buildings and Urban Habitat. On 28 September 2010 Burj Khalifa won the award for best project of year at the Middle East Architect Awards 2010.

The Council on Tall Buildings and Urban Habitat bestowed a new award for Burj Khalifa at its annual “Best Tall Buildings Awards Ceremony” on 25 October 2010 when Burj Khalifa honored as first recipient of CTBUH’s new Tall Building “Global Icon” Award. According to CTBUH the new “Global Icon” award recognizes those very special supertall skyscrapers that make a profound impact, not only on the local or regional context, but on the genre of tall buildings globally. Which is innovative in planning, design and execution, the building must have influenced and reshaped the field of tall building architecture, engineering, and urban planning. It is intended that the award will only be conferred on an occasional basis, when merited by an exceptional project perhaps every ten or fifteen years.

CTBUH Awards Chair Gordon Gill, of Adrian Smith + Gordon Gill Architecture said:

"There was discussion amongst members of the jury that the existing ‘Best Tall Building of the Year’ award was not really appropriate for the Burj khalifa. We are talking about a building here that has changed the landscape of what is possible in architecture a building that became internationally recognized as an icon long before it was even completed. ‘Building of the Century’ was thought a more appropriate title for it."

BASE jumping
The building has been used by several experienced BASE jumpers for both authorized and unauthorized BASE jumping:
 * In May 2008, Hervé Le Gallou and an unnamed British man, dressed as engineers, illegally infiltrated Burj Khalifa (around 650 m at the time), and jumped off a balcony situated a couple of floors below the 160th floor.
 * On 8 January 2010, with permission of the authorities, Nasr Al Niyadi and Omar Al Hegelan, from the Emirates Aviation Society, broke the world record for the highest BASE jump from a building after they leapt from a crane suspended platform attached to the 160th floor at 672 m. The two men descended the vertical drop at a speed of up to 220 km/h, with enough time to open their parachutes 10 seconds into the 90 second jump.

New Year's Eve fireworks display
On 31 December, 2010 fireworks accompanied by lasers and lights were displayed from the Burj Khalifa, making it the highest New Year fireworks display in the world.

The theme of the 2011 New Year fireworks was the "New Year Gala," a tribute to the spirit of Dubai, which is home to over 200 nationalities. The display also marked the first anniversary of Burj Khalifa.

Labour controversy
Burj Khalifa was built primarily by workers from South Asia. On 17 June 2008, there were 7,500 skilled workers employed at the construction site. Press reports indicated in 2006 that skilled carpenters at the site earned UK£4.34 a day, and labourers earned UK£2.84. According to a BBC investigation and a Human Rights Watch report, the workers were housed in abysmal conditions, their pay was often withheld, their passports were confiscated by their employers, and they were working in hazardous conditions that resulted in an apparently high number of deaths and injuries on site. During the building of the Burj Khalifa tower only one construction-related death was reported. However workplace injury and fatality in the UAE are "poorly documented".

On 21 March 2006, about 2,500 workers, who were upset over buses that were delayed for the end of their shifts, protested, damaging cars, offices, computers, and construction equipment. A Dubai Interior Ministry official said the rioters caused almost UK£500,000 in damage. Most of the workers involved in the riot returned the following day but refused to work.