The Burj Khalifa (Arabic: برج خليفة‎, Arabic for "Khalifa Tower"; pronounced English: /ˈbɜːrdʒ kəˈliːfə/), 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) and a roof height (excluding antenna) 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.^[2][3]

Construction of the Burj Khalifa began in 2004, with the exterior completed five years later in 2009. The primary structure is reinforced concrete. The building was opened in 2010 as part of a new development called Downtown Dubai. It is designed to be the centrepiece of large-scale, mixed-use development. The decision to construct the building is based on the government's decision to diversify from an oil-based economy, and for Dubai to gain international recognition. The building was originally named Burj Dubai but was renamed in honour of the ruler of Abu Dhabi and president of the United Arab Emirates, Khalifa bin Zayed Al Nahyan;^[4] Abu Dhabi and the UAE government lent Dubai money to pay its debts. The building broke numerous height records, including its designation as the tallest building in the world.

Burj Khalifa was designed by Adrian Smith, of Skidmore, Owings & Merrill, whose firm designed the Willis Tower and One World Trade Center. Hyder Consulting was chosen to be the supervising engineer with NORR Group Consultants International Limited chosen to supervise the architecture of the project. The design is derived from the Islamic architecture of the region, such as in the Great Mosque of Samarra. The Y-shaped tripartite floor geometry is designed to optimize residential and hotel space. A buttressed central core and wings are used to support the height of the building. Although this design was derived from Tower Palace III, the Burj Khalifa's central core houses all vertical transportation with the exception of egress stairs within each of the wings.^[5] The structure also features a cladding system which is designed to withstand Dubai's hot summer temperatures. It contains a total of 57 elevators and 8 escalators.

At a certain point in the architectural and engineering process, the original Emaar developers ran into financial issues, and required more money and economic funding. Sheikh Khalifa, the ruler of the United Arab Emirates, granted monetary aid and funding, hence resulting in the changing of the name to "Burj Khalifa". The concept of profitability derived from building high density developments and malls around the landmark have proven successful. Its surrounding malls, hotels and condominiums in Downtown Dubai have generated the most revenue from the project as a whole, while the Burj Khalifa itself made little or no profit.^[6][7]

Critical reception to Burj Khalifa has been generally positive, and the building has received many awards. There were complaints concerning migrant workers from South Asia who were the primary building labor force. These centered on low wages and the practice of confiscating passports until duties were complete.^[8] Several suicides were reported.^[9]

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^[10][11] and is part of the 2 km2 (490-acre) Downtown Dubai development 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 as chief architect, and Bill Baker as chief structural engineer.^[12][13] The primary contractor was Samsung C&T of South Korea.^[14]

Burj Khalifa was designed to be the centerpiece of a large-scale, mixed-use development to include 30,000 homes, nine hotels (including The Address Downtown Dubai), 3 hectares (7.4 acres) of parkland, at least 19 residential skyscrapers, the Dubai Mall, and the 12-hectare (30-acre) artificial Burj Khalifa Lake. The decision to build Burj Khalifa was reportedly based on the government's decision to diversify from an oil-based economy to one that is service and tourism based. According to officials, it was necessary for projects like Burj Khalifa to be built in order 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.^[15] The tower was known as Burj Dubai ("Dubai Tower") until its official opening in January 2010.^[16] It was renamed in honour of the ruler of Abu Dhabi, Khalifa bin Zayed Al Nahyan; Abu Dhabi and the federal government of UAE lent Dubai tens of billions of US dollars so that Dubai could pay its debts – Dubai borrowed at least $80 billion for construction projects.^[16] In the 2000s, Dubai started diversifying its economy but it suffered from an economic crisis in 2007–2010, leaving large-scale projects already in construction abandoned.^[17]

The Burj Khalifa set several world records, including:

There are unconfirmed reports of several planned height increases since its inception. Originally proposed as a virtual clone of the 560 m (1,837 ft) Grollo Tower proposal for Melbourne, Australia's Docklands waterfront development, the tower was redesigned by Skidmore, Owings and Merrill.^[30] Marshall Strabala, a Skidmore, Owings and Merrill architect who worked on the project until 2006, said in late 2008 that Burj Khalifa was designed to be 808 m (2,651 ft) tall.^[31]

The architect who designed it, 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 its height. It was stated that this change did not add any floors, which fit with Smith's attempts to make the crown more slender.^[32] The building opened on 4 January 2010.^[10][11]

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.^[33][34] Due to its tubular system, proportionally only half the amount of steel was used in the construction, compared to the Empire State Building.^[33][35] 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.^[36] 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.^[37] According to Strabala, 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.^[31]

Subsequent to the original design by Skidmore, Owings and Merrill, Emaar Properties chose Hyder Consulting to be the supervising engineer and NORR Group Consultants International Ltd to supervise the architecture of the project.^[38] Hyder was selected for their expertise in structural and MEP (mechanical, electrical and plumbing) engineering.^[39] Hyder Consulting's role was to supervise construction, certify the architect's design, and be the engineer and architect of record to the UAE authorities.^[38] NORR's role was the supervision of all architectural components including on-site supervision during construction and design of a 6-story addition to the office annex building for architectural documentation. NORR was also responsible for the architectural integration drawings for the Armani Hotel included in the Tower. Emaar Properties also engaged GHD,^[40] an international multidisciplinary consulting firm, to act as an independent verification and testing authority for concrete and steelwork.

The design is derived from Islamic architecture.^[19] As the tower rises from the flat desert base, there are 27 setbacks in a spiral pattern, decreasing the cross section of the tower as going upward and creating convenient outdoor terraces. These setbacks are arranged and aligned in a way that minimizes vibration wind loading from eddy currents and vortices.^[5] At the top, the central core emerges and is sculpted to form a finishing spire. At its tallest point, the tower sways a total of 1.5 m (4.9 ft).^[41]

The spire of Burj Khalifa is composed of more than 4,000 tonnes (4,400 short tons; 3,900 long tons) of structural steel. The central pinnacle pipe weighs 350 tonnes (390 short tons; 340 long tons) and has a height of 200 m (660 ft). The spire also houses communications equipment.^[42] This 244-metre spire is widely considered vanity height, since very little of its space is usable. Without the spire, Burj Khalifa would be 585 meters tall. This was reported in a Council on Tall Buildings and Urban Habitat study, which notes that the empty spire "could be a skyscraper on its own".^[43] Such a skyscraper, if located in Europe, would be the 11th tallest building on that continent.^[44]

In 2009, architects announced that more than 1,000 pieces of art would adorn the interiors of Burj Khalifa, while the residential lobby of Burj Khalifa would display the work of Jaume Plensa.^[45]

The cladding system consists of 142,000 m2 (1,528,000 sq ft) of more than 26,000 reflective glass panels and aluminium and textured stainless steel spandrel panels with vertical tubular fins.^[42] The architectural glass provides solar and thermal performance as well as an anti-glare shield for the intense desert sun, extreme desert temperatures and strong winds. The glass covers more than 174,000 m2 (1,870,000 sq ft) in area. The Burj's typical curtain wall panels measure 4'6" wide by 10'8" high and weigh about 800 pounds each, with wider panels near the buildings edges and taller ones near the top.^[46]

The exterior temperature at the top of the building is thought to be 6 °C (11 °F) cooler than at its base.^[47]

A 304-room Armani Hotel, the first of four by Armani, occupies 15 of the lower 39 floors.^[2][48] The hotel was supposed to open on 18 March 2010,^[49][50] but after several delays, it finally opened to the public on 27 April 2010.^[51] The corporate suites and offices were also supposed to open from March onwards,^[52] yet the hotel and observation deck remained the only parts of the building which were open in April 2010.

The sky lobbies on the 43rd and 76th floors house swimming pools.^[53] Floors through to 108 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 is located on the 76th floor of the tower. Corporate offices and suites fill most of the remaining floors, except for the 122nd, 123rd and 124th, where the At.mosphere restaurant, sky lobby and an indoor and outdoor observation deck are located respectively. In January 2010, it was planned that Burj Khalifa would receive its first residents from February 2010.^[53][54]

The building has 57 elevators and 8 escalators.^[42] The elevators have a capacity of 12 to 14 people per cabin, the fastest rising and descending at up to 10 m/s (33 ft/s) for double-deck elevators. However, the world's fastest single-deck elevator still belongs to Taipei 101 at 16.83 m/s (55.2 ft/s). Engineers had considered installing the world's first triple-deck elevators, but the final design called for double-deck elevators.^[22] The double-deck elevators are equipped with entertainment features such as LCD displays to serve visitors during their travel to the observation deck.^[55] The building has 2,909 stairs from the ground floor to the 160th floor.^[56]

The Burj Khalifa's water system supplies an average of 946,000 L (250,000 U.S. gal) of water per day through 100 km (62 mi) of pipes.^[19][57] An additional 213 km (132 mi) of piping serves the fire emergency system, and 34 km (21 mi) supplies chilled water for the air conditioning system.^[57] The waste water system uses gravity to discharge water from plumbing fixtures, floor drains, mechanical equipment and storm water, to the city municipal sewer.^[58]

The air conditioning system draws air from the upper floors where the air is cooler and cleaner than on the ground.^[59] At peak cooling times, the tower's cooling is 46 MW (62,000 hp), equivalent to that provided by 13,000 short tons (26,000,000 lb; 12,000,000 kg) of melting ice in one day.^[57] Water is collected via a condensate collection system and is used to irrigate the nearby park.^[19]

To wash the 24,348 windows, totaling 120,000 m2 (1,290,000 sq ft) of glass, the building has three horizontal tracks which each holding a 1,500 kg (3,300 lb) bucket machine. Above level 109, and up to tier 27, traditional cradles from davits are used. The top of the building is cleaned by a crew that uses ropes to descend from the top to gain access.^[60][61] Under normal conditions, when all building maintenance units are operational, it takes 36 workers three to four months to clean the entire exterior.^[42][62]

Unmanned machines clean the top 27 additional tiers and the glass spire. The cleaning system was developed in Melbourne, Australia, by CoxGomyl, a manufacturer of building maintenance units,^[63] at a cost of A$8 million.^[62]

Outside, WET Enterprises designed a fountain system at a cost of Dh 800 million (US$217 million). Illuminated by 6,600 lights and 50 coloured projectors, it is 270 m (900 ft) long and shoots water 150 m (500 ft) into the air, accompanied by a range of classical to contemporary Arabic and other music. It is the world's second largest choreographed fountain.^[64] On 26 October 2008, Emaar announced that based on results of a naming contest the fountain would be called the Dubai Fountain.^[65]

An outdoor observation deck, named At the Top, opened on 5 January 2010 on the 124th floor. At 452 m (1,483 ft), it was the highest outdoor observation deck in the world when it opened.^[66] Although it was surpassed in December 2011 by Cloud Top 488 on the Canton Tower, Guangzhou at 488 m (1,601 ft),^[67] Burj Khalifa opened the 148th floor SKY level at 555 m (1,821 ft), once again giving it the highest observation deck in the world on 15 October 2014,^[68][69] until the Shanghai Tower opened in June 2016 with an observation deck at a height of 561 metres. The 124th floor observation deck also features the electronic 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.^[70][71][72] To reduce the daily rush of sightseers, management allows visitors to purchase tickets in advance for a specific date and time, at a 75% discount on tickets purchased on the spot.^[73] Tickets start at 135 AED, or US$36.75.

On 8 February 2010, the observation deck was closed to the public for two months after power-supply problems caused an elevator to become stuck between floors, trapping a group of tourists for 45 minutes.^{[74][75][76][77][78]} When the tide is low and visibility is high, people can see the shores of Iran from the top of the skyscraper.^[79]

Burj Khalifa is surrounded by an 11 ha (27-acre) park designed by landscape architects SWA Group.^[80] Like the tower, the park's design was based on the flower of the Hymenocallis, a desert plant.^[81] At the centre of the park is the water room, which is a series of pools and water jet fountains. Benches and signs incorporate images of Burj Khalifa and the Hymenocallis flower.^[82]

The plants are watered by water collected from the building's cooling system. The system provides 68,000,000 L (15,000,000 imp gal) annually.^[82] WET Enterprises, who also developed the Dubai Fountain, developed the park's six water features.^[83]

On the higher floors, the sun can still be seen for several minutes after it has set at ground level. This has led Dubai clerics to rule that those living above the 80th floor should wait 2 additional minutes to break their Ramadan fast, and those living above the 150th floor, 3 minutes.^[86]

The tower was constructed by Samsung C&T from South Korea, which also did work on the Petronas Twin Towers and Taipei 101.^[87] Samsung C&T built the tower in a joint venture with BESIX from Belgium and Arabtec from the UAE.^[88][89] Turner was the project manager on the main construction contract.^[90] Hong Kong-based Far East Aluminum combined to provide the exterior cladding for Burj Khalifa.^[91][92]

The contractor and the engineer of record was Hyder Consulting.^[93] 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.^[21] 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.^[12] 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 record delivery height of 606 m (1,988 ft),^[21] the 156th floor. Three tower cranes were used during construction of the uppermost levels, each capable of lifting a 25-tonne load.^[94] The remaining structure above was constructed of lighter steel.

In 2003, 33 test holes were drilled to study the strength of the bedrock underlying the structure.^[95] "Weak to very weak sandstone and siltstone" was found, just metres below the surface. Samples were taken from test holes drilled to a depth of 140 metres, finding weak to very weak rock all the way.^[96] The study described the site as part of a "seismically active area".

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 metre in diameter by 43 m in length, buried more than 50 m (164 ft) deep.^[22] 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.^[97] A cathodic protection system is under the concrete to neutralize the groundwater and prevent corrosion.^[42]

The Burj Khalifa is highly compartmentalised. 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.^[42][98]

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.^[99]

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 (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.

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).^[110] He estimated the total cost for the project to be about US$1.5 billion.^[4]

The project's completion coincided with the financial crisis of 2007–2008, and with vast overbuilding in the country, leading to high vacancies and foreclosures.^[111] 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.^[3][112]

Because of 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, 825 were still empty at that time.^[113][114] However, over the next two and a half years, overseas investors steadily began to purchase the available apartments and office space.^[115] By October 2012, Emaar reported that around 80% of the apartments were occupied.^[116]

The ceremony was broadcast live on a giant screen on Burj Park Island and on smaller screens elsewhere.^[117] Hundreds of media outlets from around the world reported live from the scene.^[118] In addition to the media presence, 6,000 guests were expected.^[119]

The opening was held on 4 January 2010.^[120] The ceremony featured a display of 10,000 fireworks, light beams projected on and around the tower, and further sound, light and water effects.^[118] The celebratory lighting was designed by UK lighting designers Speirs and Major Associates.^[121] Using the 868 powerful stroboscope lights that are integrated into the façade and spire of the tower, different lighting sequences were choreographed, together with more than 50 different combinations of other effects.

Within 17 months of the building's official opening, a man described as "an Asian in his mid-30s" who worked at one of the companies in the tower, died by suicide on 10 May 2011 by jumping from the 147th floor. He fell 39 floors, landing on a deck on the 108th floor. Dubai police confirmed the act as a suicide, reporting that "[they] also came to know that the man decided to commit suicide as his company refused to grant leave."^[122]

The Daily Mail reported that on 16 November 2014, a Portuguese national who was in Dubai on a tourist visa, fell to her death from Burj Khalifa's "At the Top" observation deck on the 148th floor.^[123] However, on 18 May 2015, Dubai police disputed the report made by the Daily Mail on this incident and said that this incident took place in Jumeirah Lakes Towers.^[124] A Dubai coroner's report stated her body was found on the third floor of the Burj Khalifa.^[125] Emails obtained under the Freedom of Information act from Portugal's embassy in the UAE also confirmed that she had committed suicide from the 148th floor of the Burj Khalifa.^[126]

The Burj Khalifa was built primarily by workers from South Asia and East Asia.^[127][128] This is generally because the current generation of UAE locals prefer governmental jobs and do not have an attitude favouring private sector employment.^[129][130] On 17 June 2008, there were about 7,500 skilled workers employed at the construction site.^[105] Press reports indicated in 2006 that skilled carpenters at the site earned £4.34 a day, and labourers earned £2.84.^[127] According to a BBC investigation and a Human Rights Watch report, the workers were housed in abysmal conditions, and worked long hours for low pay.^{[131][132][133]} During construction, only one construction-related death was reported.^[134] However, workplace injuries and fatalities in the UAE are "poorly documented", according to Human Rights Watch.^[131]

On 21 March 2006, about 2,500 workers, upset over buses that were delayed for the end of their shifts, protested and triggered a riot, damaging cars, offices, computers and construction equipment.^[127] A Dubai Interior Ministry official said the rioters caused almost £500,000 in damage.^[127] Most of the workers involved in the riot returned the following day but refused to work.^[127]

The building has been used by several experienced BASE jumpers for authorised and unauthorised BASE jumping:

On 28 March 2011, Alain "Spiderman" Robert scaled the outside of Burj Khalifa. The climb to the top of the spire took six hours. To comply with UAE safety laws, Robert, who usually climbs in free solo style, used a rope and harness.^[142]

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.^[145] On 28 September 2010 Burj Khalifa won the award for best project of the year at the Middle East Architect Awards 2010.^[146] Awards Chair Gordon Gill, of Adrian Smith + Gordon Gill Architecture, said:

Burj Khalifa was also the recipient of the following awards.^[148][149]