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.
Under UAE law, the Contractor and the Engineer of Record, 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.
The primary structure is reinforced concrete. Putzmeister created a new, super high-pressure trailer concrete pump, the BSA 14000 SHP-D, for this project. Burj Khalifa’s construction used 330,000 m3 (431,600 cu yd) of concrete and 55,000 tonnes (61,000 short tons; 54,000 long tons) of steel rebar, and construction took 22 million man-hours. In May 2008 Putzmeister pumped concrete with more than 21 MPA ultimate compressive strength of gravel that would surpass the 600 meters weight of the effective area of each column from the foundation to the next fourth level, and the rest is by metal columns jacketed or covered with concreted to a then world record delivery height of 606 m (1,988 ft), the 156th floor.
Three tower cranes were used during construction of the uppermost levels, each capable of lifting a 25-tonne load. The remaining structure above is constructed of lighter steel.
In 2003 33 test holes were drilled, to study the strength of the bedrock underlying the structure. “Weak to very weak sandstone and siltstone”was found, just metres below the surface. Samples were taken from test holes drilled to a depth of 140 metres, finding weak to very weak rock all the way. The study described the site as part of a “seismically active area”.
Over 45,000 m3 (58,900 cu yd) of concrete, weighing more than 110,000 tonnes (120,000 short tons; 110,000 long tons) were used to construct the concrete and steel foundation, which features 192 piles; each pile is 1.5 metre diameter x 43 m long, buried more than 50 m (164 ft) deep.
The foundation is designed to support the total building weight of approximately 450,000 tonnes (500,000 short tons; 440,000 long tons) 4,500 MegaNewtons or 4,500 MegaPascal. 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. A high density, low permeability concrete was used in the foundations of Burj Khalifa in which the Ultimate Compressive Strength reach as much as 30 MPa, an effective area in which concrete is sandwiched by the pile, the column is 12 meters by 12 meters and the thickness as low as possible. A cathodic protection system under the mat is used to minimise any detrimental effects from corrosive chemicals in local ground water.
The Burj Khalifa is highly compartmentalised. Pressurized, air-conditioned refuge floors are located approximately every 35 floors where people can shelter on their long walk down to safety in case of an emergency or fire.
Special mixes of concrete are made to withstand the extreme pressures of the massive building weight; as is typical with reinforced concrete construction, each batch of concrete used was tested to ensure it could withstand certain pressures. CTLGroup, working for SOM, conducted the creep and shrinkage testing critical for the structural analysis of the building.
The consistency of the concrete used in the project was essential. It was difficult to create a concrete that could withstand both the thousands of tonnes bearing down on it and Persian Gulf temperatures that can reach 50 °C (122 °F). To combat this problem, the concrete was not poured during the day. Instead, during the summer months, ice was added to the mixture and it was poured at night when the air is cooler and the humidity is higher. A cooler concrete mixture cures evenly throughout and is therefore less likely to set too quickly and crack. Any significant cracks could have put the entire project in jeopardy.
The unique design and engineering challenges of building Burj Khalifa have been featured in a number of television documentaries, including the Big, Bigger, Biggest series on the National Geographic and Five channels, and the Mega Builders series on the Discovery Channel.
