Burj Khalifa
Published on Feb 14, 2016
Abstract
Burj Khalifa known as Burj Dubai prior to its inauguration, is a skyscraper in Dubai, United Arab Emirates, and is currently the tallest structure in the world, at 828 m (2,717 ft). 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
The building is part of the new 2 km2 (490-acre) 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 and Merrill of Chicago, with Adrian Smith 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.
Facts About Burj Dubai
• 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 (1,483 ft), surpassing the 449.2 m (1,474 ft) 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 (1,671 ft) made it the world's tallest building, and level 141 reached.
• 12 August 2007: Surpasses the Sears Tower antenna, which stands 527.3 m (1,730 ft).
• 12 September 2007: At 555.3 m (1,822 ft), becomes the world's tallest freestanding structure, surpassing the CN Tower in Toronto, and level 150 reached.
• 7 April 2008: At 629 m (2,064 ft), 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 (2,087 ft) and that its final height will not be given until it is completed in September 2009.
• 1 September 2008: Height tops 688 m (2,257 ft), 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 (2,717 ft).
• 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.
WORLD RECORDS
At over 828 metres (2,716.5 feet) and more than 160 stories, Burj Khalifa holds the following records:
• Tallest building in the world
• Tallest free-standing structure in the world
• Highest number of stories in the world
• Highest occupied floor in the world
• Highest outdoor observation deck in the world
• Elevator with the longest travel distance in the world
• Tallest service elevator in the world
• Tallest of the Supertall
Not only is Burj Khalifa the world’s tallest building, it has also broken two other impressive records: tallest structure, previously held by the KVLY-TV mast in Blanchard, North Dakota, and tallest free-standing structure, previously held by Toronto’s CN Tower. The Chicago-based Council on Tall Buildings and Urban Habitat (CTBUH) has established 3 criteria to determine what makes a tall building tall. Burj Khalifa wins by far in all three categories.
a) Height to architectural top
b) Highest occupied floor
c) Height to tip
4. Structural Elements — Elevators, Spire, and More
It is an understatement to say that Burj Khalifa represents the state-of-the-art in building design. From initial concept through completion, a combination of several important technological innovations and innovation structural design methods have resulted in a superstructure that is both efficient and robust.
a) Foundation
The superstructure is supported by a large reinforced concrete mat, which is in turn supported by bored reinforced concrete piles. The design was based on extensive geotechnical and seismic studies. The mat is 3.7 meters thick, and was constructed in four separate pours totaling 12,500 cubic meters of concrete. The 1.5 meter diameter x 43 meter long piles represent the largest and longest piles conventionally available in the region. A high density, low permeability concrete was used in the foundations, as well as a cathodic protection system under the mat, to minimize any detrimental effects form corrosive chemicals in local ground water.
b) Podium
The podium provides a base anchoring the tower to the ground, allowing on grade access from three different sides to three different levels of the building. Fully glazed entry pavilions constructed with a suspended cable-net structure provide separate entries for the Corporate Suites at B1 and Concourse Levels, the Burj Khalifa residences at Ground Level and the Armani Hotel at Level 1.
c) Exterior Cladding
The exterior cladding is comprised of reflective glazing with aluminum and textured stainless steel spandrel panels and stainless steel vertical tubular fins. Close to 26,000 glass panels, each individually hand-cut, 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. The cladding system is designed to withstand Dubai's extreme summer heat, and to further ensure its integrity, a World War II airplane engine was used for dynamic wind and water testing. The curtain wall of Burj Khalifa is equivalent to 17 football (soccer) fields or 25 American football fields.
d) Structural System
In addition to its aesthetic and functional advantages, the spiraling “Y” shaped plan was utilized to shape the structural core of Burj Khalifa. This design helps to reduce the wind forces on the tower, as well as to keep the structure simple and foster constructability. The structural system can be described as a “buttressed core”, and consists of high performance concrete wall construction. Each of the wings buttress the others via a six-sided central core, or hexagonal hub. This central core provides the torsional resistance of the structure, similar to a closed pipe or axle.
Corridor walls extend from the central core to near the end of each wing, terminating in thickened hammer head walls. These corridor walls and hammerhead walls behave similar to the webs and flanges of a beam to resist the wind shears and moments. Perimeter columns and flat plate floor construction complete the system. At mechanical floors, outrigger walls are provided to link the perimeter columns to the interior wall system, allowing the perimeter columns to participate in the lateral load resistance of the structure; hence, all of the vertical concrete is utilized to support both gravity and lateral loads. The result is a tower that is extremely stiff laterally and torsionally. It is also a very efficient structure in that the gravity load resisting system has been utilized so as to maximize its use in resisting lateral loads.
As the building spirals in height, the wings set back to provide many different floor plates. The setbacks are organized with the tower’s grid, such that the building stepping is accomplished by aligning columns above with walls below to provide a smooth load path. As such, the tower does not contain any structural transfers. These setbacks also have the advantage of providing a different width to the tower for each differing floor plate. This stepping and shaping of the tower has the effect of “confusing the wind”: wind vortices never get organized over the height of the building because at each new tier the wind encounters a different building shape.
e) Spire
The crowning touch of Burj Khalifa is its telescopic spire comprised of more than 4,000 tons of structural steel. The spire was constructed from inside the building and jacked to its full height of over 200 metres (700 feet) using a hydraulic pump. In addition to securing Burj Khalifa's place as the world's tallest structure, the spire is integral to the overall design, creating a sense of completion for the landmark. The spire also houses communications equipment.
f) Mechanical Floors
Seven double-storey height mechanical floors house the equipment that bring Burj Khalifa to life. Distributed around every 30 storeys, the mechanical floors house the electrical sub-stations, water tanks and pumps, air-handling units etc, that are essential for the operation of the tower and the comfort of its occupants.
g) Window Washing Bays
Access for the tower's exterior for both window washing and façade maintenance is provided by 18 permanently installed track and fixed telescopic, cradle equipped, building maintenance units. The track mounted units are stored in garages, within the structure, and are not visible when not in use. The manned cradles are capable of accessing the entire facade from tower top down to level seven. The building maintenance units jib arms, when fully extended will have a maximum reach of 36 meters with an overall length of approximately 45 meters. When fully retracted, to parked position, the jib arm length will measure approximately 15 meters. Under normal conditions, with all building maintenance units in operation, it will take three to four months to clean the entire exterior facade.
h) Broadcast and Communications Floors
The top four floors have been reserved for communications and broadcasting. These floors occupy the levels just below the spire
Mechanical, Electrical & Plumbing
To achieve the greatest efficiencies, the mechanical, electrical and plumbing services for Burj Khalifa were developed in coordination during the design phase with cooperation of the architect, structural engineer and other consultant.
•The tower's water system supplies an average of 946,000 litres (250,000 gallons) of water daily
•At peak cooling, Burj Khalifa will require about 10,000 tons of cooling, equal to the cooling capacity provided by about 10,000 tons of melting ice
•Dubai's hot, humid climate combined with the building's cooling requirements creates a significant amount of condensation. This water is collected and drained in a separate piping system to a holding tank in the basement car park
•The condensate collection system provides about 15 million gallons of supplement water per year, equal to about 20 Olympic-sized swimming pools
•The tower's peak electrical demand is 36mW, equal to about 360,000 100 Watt bulbs operating simultaneously
WIND ENGINEERING
For a building of this height and slenderness, wind forces and the resulting motions in the upper levels become dominant factors in the structural design. An extensive program of wind tunnel tests and other studies were undertaken (Figure 11). The wind tunnel program included rigid-model force balance tests, full multi-degree of freedom aeroelastic model studies, measurements of localized pressures, pedestrian wind environment studies, and wind climatic studies. Wind tunnel models account for the cross-wind effects of wind-induced vortex shedding on the build¬ing (Figure 12). The aeroelastic and force balance studies used models mostly at 1 : 500 scale.
To determine the wind loading on the main structure, wind tunnel tests were undertaken early in the design using the high-frequency force-balance technique. The wind tunnel data were then com¬bined with the dynamic properties of the tower in order to compute the tower's dynamic response and the overall effective wind force distributions at full scale. For the Burj Dubai the results of the force balance tests were used as early input for the structural design and detailed shape of the tower and allowed parametric studies to be undertaken on the effects of varying the tower's stiffness and mass distribution.
The building has essentially six important wind directions. The principal wind directions are when the wind is blowing into the 'nose'/'cutwater' of each of the three wings (Nose A, Nose B, and Nose C). The other three directions are when the wind blows in between two wings, termed the 'tail' direc¬tions (Tail A, Tail B, and Tail C). It was noticed that the force spectra for different wind directions showed less excitation in the important frequency range for winds impacting the pointed or nose end of a wing (Figure 13) than from the opposite direction (tail). This was borne in mind when selecting the orientation of the tower relative to the most frequent strong wind directions for Dubai and the direction of the set backs.