Ambitious engineering construction projects in Dubai have always been drawing the world’s attention. I recently visited the Emirates for the first time and could not believe that less than 20 years ago most of the infrastructure did not exist. The engineering feats that they have overcome demonstrate the capability of continually advancing to bigger and better projects and the Burj Khalifa is a prime example of this. If they can build a city in the sea, why not build a city in the sky.
The Burj Khalifa is an iconic tower that appears illusionary. Its sheer size and spectacular structure seems beyond comprehension. It towers up out of the desert and extends way beyond its neighbouring skyscrapers. At 828m it is the tallest free standing structure in the world. Comprising of a record breaking 162 floors, the Burj accommodates 900 luxury apartments. Also included are the Armani hotel, restaurants, offices and a leisure club.
The desert Burj Khalifa sits on consists of 4m of sand followed by a mixture of weak sandstones and limestones. Extensive seismic studies were carried out to design foundations capable of supporting the 500,000 tonnes structure on such weak ground. 192 Skin Friction Piles, 50 meters deep and 1.5 meters in diameter support the structure by using friction between the side of each pile and the surrounding sand. On top of the piles sits a 3.7 meter raft of solid concrete that forms the base of the tower.
Unlike previous skyscrapers, Burj Khalifa’s height requires a wider base that must taper with height, otherwise the mass of the tower would be too great. Engineers developed the design of a three winged buttress core, imitating the shape of the Hymenocallis desert flower. A hexagonal central core reduces the torque forces and the three wings, with a central concrete spine from end to end, provide the stability essential for a structure of such height.
Wind tunnels tested the effects of wind induced vortex shedding on the building that would cause the building to sway from side to side. Tests were carried out on a 1:500 scale model (smaller than the average height of a British man). The resulting design steps back at 26 different locations as the tower gains height. A regular change in width and shape of the structure prevents wind vortexes from coalescing. This protects the building from vortexes caused by wind speeds of around 160 km/hr. This produces the spiralling Y-shaped patterned structure that eventually reduces to form the 136m steel spire emerging from the top of the tower.
The Burj was built from steel and reinforced concrete in a process called Jump Forming. A mould containing steel reinforcement bars are filled with concrete. After 12 hours the concrete gets dry and the moulds are lifted to the next level. A new set of steel bars is then installed and the process is repeated. The efficiency of this method allowed the tower to grow at a maximum rate of a new storey every 3 days.
World class engineers and labourers of over 100 nationalities worked on building the Burj Khalifa. Excavation of the site began in January 2004 and the tower officially opened 6 years later. The total cost of construction amounted to $1.5 billion. At peak construction 12,000 labourers were on site accumulating a total of 22 million man hours over 6 years.
The exterior of the structure is glass panelled to give it a glittering appearance. Each of the 24,348 glass panels is 6.4 metres long. The panels are double coated: silver on the interior, reflecting UV and titanium on the exterior, reflecting infra-red. Had these coatings not been applied, the extreme temperatures of middle-eastern climate would result in the interior of the Burj reaching temperatures of 98ºC.
The amount of cooling required to keep the Burj Khalifa air-conditioned is equivalent to around 10,000 tonnes of melting ice. A condensation collection system stores 15 million gallons of condensation from the surrounding humid air each year. Water is stored underneath the building which is then recycled in irrigation systems of the surrounding gardens.
Future of Burj Khalifa
Since being announced as hosts of the 2020 Expo, Dubai has launched a multitude of further development projects including a 3km canal, the Taj Arabia (a replica of India’s Taj Mahal), ‘District 1’ which will include the largest inland crystal lagoon body of water in the world with seven kilometres of lagoons, and development of the Palm Deira island adding another 40 km to Dubai’s coastline. In the hot climates of the UAE and under tight timescales, it will be interesting to see how engineers face the huge challenges involved in turning these audacious projects into reality.
Written by a guest blogger Ellie Russell.