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Structural Details of Burj Khalifa – Concrete Grade and Foundations

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Structural Details of Burj Khalifa

The world’s tallest building, Burj Khalifa took 6 years for its construction and was inaugurated on 4th January 2010. The structure is 828m tall and the whole system is a reinforced concrete tower structure. This was the first attempt in world history to have such a large height for structures. This reason made the designers to employ one of the best and latest technology and innovative structural design. The structural features of Burj Khalifa is explained in the following section.

Fig.1: Burj Khalifa

Burj Khalifa Project Details

The structure is located in Dubai, United Arab Emirates. The structural features include: The tower comprises 2,80,000 m2 area. This area is utilized for 700 residential apartments located from 45 to 108 floors. Remaining spaces is till the 160th floor is occupied by the corporate officers. The total project cost is estimated to be US$20billion. The tower construction itself costs $4.2billion. The structural elements used and their amount is mentioned below:
  1. Concrete Used = 250000 cubic meter
  2. Curtain Walls = 83,600sq.m of glass and 27,900 sq.m of metal
  3. Steel Rebars Used = 39,000 tones
  4. Man-Hours = 22million man-hours

Shape of the Tower

Adrian Smith is the man behind the structural and the architectural design of Burj Khalifa. The basic structure is a central hexagon core with three wings, which is clustered around it, as shown in figure-2. While moving up along the tower, one wing at each tier is set back. This makes decreasing cross section when moving up. The structure consists of 26 terraces.

Fig.2: Cross Section plan of Burj Khalifa

Structural System of Burj Khalifa

The Burj Khalifa employs a ‘Y’ shaped floor plan. This plan provide higher performance and provides a full view of the Persian Gulf. The shape and the upward setbacks help the structure to reduce the wind forces that is acting on the structure. The shape was finally fixed based on the series of wind tunnel tests. The structural system employed for Burj Khalifa can be called as the Buttressed Core System. The whole system is constructed by using high performance concrete wall. Each wing buttresses the other through a hexagonal central core as shown in figure-2. The central core has a higher resistance towards the torsional resistance. The structure is more designed for wind force and related effects. There are corridor walls that extend from the central core to the end of the wing. At the end, these walls are thickened by means of hammer walls. These walls resist the wind shears and moments by acting like the web and the flanges of the beams. There are perimeter columns which are connected to the mechanical floors. The connection between the perimeter columns and the mechanical floors is provided by means of outrigger walls. This help to resists higher wind loads laterally. The outrigger depth is three storey heights. There is periodic encounter of outrigger system through the height of the tower.

High Performance Concrete Used in Concrete

The high-performance concrete used in Burj Khalifa guarantee low permeability and higher durability. The C80 and C60 cube strength concrete is used incorporating fly ash, Portland cement, and the local aggregates. A young’s modulus of 43800N/mm2 is said to be granted by the C80 concrete. The largest concrete pumps in the world were used to pump concrete to height up to 600 m at a single stage. Two numbers of this type of pump was used. As the temperature of the location (Dubai) is very high, there were chance of cracks due to shrinkage. So, the concrete pouring process was carried out at night at a cooler temperature. Ice was added to the concrete mix to facilitate the desired temperature. To withstand the excessive pressure caused due to the building weight, special concrete mixes were employed. Every batch was tested before placing.

Foundation of Burj Khalifa

The superstructure of Burj Khalifa is supported over a large reinforced concrete raft. This raft is in turn supported by bored reinforced concrete piles. The raft has a thickness of 3.7m and was constructed in four separate pours. The grade of concrete raft is C50 which was self-consolidating concrete. The concrete volume used in the raft is 12,500 meter cube. The number of piles used were 194. The piles were 1.5m in diameter and have a length of 43m. Each pile has a capacity of 3000 tons. The concrete grade used in piles where C60 SCC concrete which were placed by tremie method. This utilized polymer slurry to carry out the process. To reduce the detrimental effects of chemicals, cathodic protection where provided under the raft.

Fig.3: Pile Raft Foundation in Burj Khalifa. Photos From the Construction Stage

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