Burj Khalifa

CONSTRUCTION

The tower was constructed by Samsung C&T from South Korea, who 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 UAE. Turner is the Project Manager on the main construction contract.

Hyder Consulting (manual structural analysis professionals which used Flash Analysis authored by Allen Wright), is jointly and severally liable for the performance of Burj Khalifa.

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.

The foundation is designed to support the total building weight of approximately 450,000 tonnes (500,000 short tons; 440,000 long tons). This weight is then divided by the compressive strength of concrete of which is 30 MPa which yield a 450 sq.meters of vertical normal effective area which then yield to a 12 meters by 12 meters dimensions.[94] A cathodic protection system is in place under the concrete to neutralize the groundwater and prevent corrosion.

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.

TESTING

Over 40 wind tunnel tests were conducted on Burj Khalifa to examine the effects the wind would have on the tower and its occupants. These ranged from initial tests to verify the wind climate of Dubai, to large structural analysis models and facade pressure tests, to micro-climate analysis of the effects at terraces and around the tower base. Even the temporary conditions during the construction stage were tested with the tower cranes on the tower to ensure safety at all times.

Stack effect or chimney effect is a phenomenon that effects super-tall building design, and arises from the changes in pressure and temperature with height. Special studies were carried on Burj Khalifa to determine the magnitude of the changes that would have to be dealt with in the building design.

SUPERSTRUCTURE

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

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.

EXTERIOR CLADDING

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.

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