Page D3.2 . 26 May 2010                     
ArchitectureWeek - Design Department
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Burj Khalifa

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Conceived as the Tallest

Emaar Properties, the developers of the Burj, intended right from the start to build the world's tallest structure, asking for schemes for a 550-meter (1,804-foot) skyscraper from a number of firms — among them Pelli Clarke Pelli, Kohn Pedersen Fox, and Carlos A. Ott, along with SOM.

According to SOM partner George Efstathiou, SOM won the commission partly because the firm could service such a complex project with in-house interiors, mechanical, and structural expertise, such as SOM structural and civil engineering partner William F. Baker. The design evolved through collaboration among those SOM entities, Efstathiou says.

The biggest influence on the building's design was wind load. The skyscraper's form is crafted to break down the cumulative effects of high winds. The Burj has a Y-shaped footprint — a plan shape that SOM has found to be optimal for residential buildings.

Relatively narrow wings extend out from a central core, permitting much of the stabilizing structure to be concentrated at the center. In the wings, residential spaces on either side of a double-loaded corridor are thus minimally intruded upon by structure.

The tower is broad at its base and becomes more slender as it rises. Floors 1 to 8 are dedicated to a hotel; hotel residences and suites occupy floors 9 to 39; private condominiums occupy floors 44 to 108; and floors 111 to 154 contain office spaces. Several intermediate floors and those above 160 (the highest habitable floor) are devoted to mechanical space. The 124th floor holds the tower's observation deck, which reopened in early April after an elevator accident prompted its closure in February.

As the tower rises, each of the three wings sets back at different heights, in a clockwise spiral pattern. This gives the tower a variegated form to "confuse the wind," according to William Baker and his colleagues D. Stanton Korista and Lawrence C. Novak. As the engineers describe the strategy in a technical paper, "The wind vortices never get organized because at each new tier the wind encounters a different building shape."

The stepping and spiraling benefits the tower aesthetically. Whatever your opinion about constructing a gargantuan energy hog in the desert, there is no question that the Burj is an elegant object, one of the few contemporary tall structures to strike a chord with classical skyscraper design from the 1920s and '30s. Not since Pelli's Petronas Towers has a building so lithely reached into the heavens. Above the highest occupiable floor (160) is a 70-meter- (230-foot-) tall steel spire made of 11.4-centimeter- (4.5-inch-) steel tubing, which makes the Burj appear to disappear into thin air.

Materials and Finishes

The tower's slender shape is achieved with a structure of concrete, not steel. Not only was steel cost-prohibitive, but concrete structures are generally better for residential uses because the floor slabs and ceilings are easier to customize, along with the location of walls. Concrete also helps to stabilize such a tall building, which would have been subject to greater movement and vibration due to wind loads if it were steel.

SOM pioneered a "buttressed core" structural strategy in which the center hexagonal walls are buttressed by the wing walls. The core walls "provide the torsional resistance of the structure," according to Baker and his colleagues, "similar to closed tube or axel." The tower is constructed on a 3.7-meter- (12-foot-) thick high-strength reinforced concrete raft foundation supported by 194 cast-in-place friction piles, each about 43 meters (141 feet) long.

The curtain wall — similar to one used by SOM on the Trump International Hotel & Tower in Chicago (2009), another Smith-Baker project — is an aluminum-frame system with textured stainless-steel spandrel panels.

What makes the Burj glisten on the skyline are vertical polished stainless-steel fins with an elongated shape in plan, spaced 1.5 meters (4.9 feet) around the building, extending out about 23 centimeters (nine inches), and about 13 centimeters (five inches) at their widest. The fins catch the light and reflect it, exaggerating the tower's height.

Biggest – but Brightest?

As I mentioned, the world is different now than it was when the concept for the Burj first jelled in early 2003. When I asked Efstathiou if sustainability was a client concern, he admitted that it was not, noting that "back then it was not as important."

Maybe not in Dubai.

There are a few nods to conservation. Condensate water from the air-conditioning system is collected (57 million liters per year, or 15 million gallons, according to SOM) for landscape irrigation. But why use water-thirsty landscaping in the desert?

The tower's height allows cooler air near its top — which is about seven degrees Celsius (13 degrees Fahrenheit) cooler than ambient air at ground level — to be pulled into the HVAC system; SOM calls this "skysourcing."

But SOM’s press materials point out some astounding numbers: at peak, the Burj requires 11,300 metric tons (12,500 tons) of cooling per hour, the tower consumes 946,000 liters (250,000 gallons) of water a day, and peak electrical demand is roughly equivalent to a half-million 100-watt light bulbs.

What is the long-term cost of such a building to the environment, including dwindling water supplies? Are there better, smarter ways of building at high density that consume far fewer resources?

The emirate that saved the Burj from default is exploring some possibilities. Described as a "green" city of the future, Masdar City is to be built on the coast in Abu Dhabi. The six-square-kilometer (2.3-square-mile) city for 50,000 people, planned by Foster + Partners, is being built in two phases. The first entails the construction of a huge photovoltaic (PV) plant that will power the city to be constructed next to it.

The most important design features of Masdar are easy access to public transportation and the use of traditional design to aid in cooling the city. The intent is to ban cars from Masdar, keep the city walkable, and ensure public transport throughout, with access no farther than 200 meters (660 feet) from any given point, and options including mass transit and a fully automated personal rapid transit system.

As for mitigating the desert climate, dappled narrow streets will weave through neighborhoods, shaded with canopies that convert sunlight into electrical energy. Canals lining the mews will help bring air temperatures down though moisture — a very old yet effective technique for temperature control in the desert.

Outside the city, a cluster of facilities and generation plants is planned: fields of PV collectors, a collection of solar mirrors to produce steam for heating and cooling, a wind farm, water and sewage treatment plants, recycling centers. The goal is to create a city without waste. Services such as a desalination plant will help Masdar be self-sufficient.

In an interesting twist, Adrian Smith + Gordon Gill Architecture, the firm that Smith cofounded after he designed the Burj and left SOM, is designing the headquarters building for Masdar City, to be completed this year.

Should it be done? The Burj Khalifa is an elegant design for such an enormous object. It unquestionably represents a striking engineering achievement. But it also seems to represent an enormously costly stunt — as measured in resources, money aside — of the kind our planet cannot continue to afford.   >>>

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Michael J. Crosbie is editor-in-chief of Faith & Form, the chair of the University of Hartford’s Department of Architecture, and a contributing editor to ArchitectureWeek.   More by Michael J. Crosbie

 

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The glass-and-steel clad Burj Khalifa has 160 habitable floors.
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The main entries into the Burj Khalifa can be found at the joints between its three wings.
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On the 124th floor, there is an open-air observation deck.
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Plan diagrams comparing the Burj Khalifa with other notable skyscrapers.
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A ground-floor lobby in the Burj Khalifa.
Photo: Courtesy Emaar Properties

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Over 50 double-deck elevators service the Burj Khalifa, with the capacity for 21 people on each deck.
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The tower dwarfs its low-rise surroundings.
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Aerial view of the Burj Khalifa.
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