By Construction Week Staff Writer
From the concrete in its foundations to the spire at the top, a look at how the Burj Khalifa was put together.
From the concrete in its foundations to the spire at the top, a look at how the Burj Khalifa was put together.
Vision is a word you hear a lot in the GCC. But just imagine if you will, sitting down in a meeting and deciding to construct the world's tallest building in your city. Not one that is going to be the tallest by a few dozen metres, and relinquish its title to another tower, in another city, within a few years, but the tallest by a massive margin.
If you can imagine that, then you can get a feeling for the vision that went into coming up with the Burj Khalifa, now open and officially the world's tallest tower, a whopping 300m-plus taller than the next nearest rival. More than six years in the making and not fully-finished just yet, the project was and is a massive undertaking, one that has paired bold vision with a brave leap into the engineering unknown.
Making it happen not only needed vision, but cash and a fair whack of design and engineering genius. Pushing at the envelope of engineering means trying new things, developing new techniques and doing a ton of testing.
And while it's hard to find a construction contractor or supplier who doesn't claim to have been involved in the making of the Burj Khalifa, CW takes a look at what those who were really there had to do to build an icon.
Once you've had the vision, the real work doesn't start until you find a way to pay. The final finished cost of the Burj Khalifa will be tough to calculate, once a complete interior fit-out is taken into account. Mohammed Alabbar himself recently suggested a final budget of US $1.5 billion. Mashreqbank , Emirates Bank International and Abu Dhabi Commercial Bank formed a syndicate to provide finance way back in 2005.
The triumvirate of banks signed a financing agreement with Korean contractor Samsung Corporation and its project partners Belhasa Six Construct and Arabtec. The good news is that around 90% of saleable space was sold off-plan, helping ensure that money never ran tight.
Skidmore, Owings & Merrill was the architecture firm behind the design and engineering of the tower.
The design team developed what has become known as a spiraling "Y" shaped plan, which was used to shape the structural core of the building.
Key considerations included the impact of wind forces and ‘constructability', architecture cant for practical construction considerations. The design employs a ‘buttressed core', which has each wing of the building buttressing the others via a six-sided central core.
It is this central core that provides the structure's torsional resistance. The design of wall and corridor intersections means that all of the vertical concrete is used to support both gravity and lateral loads.
As the building spirals in height, the wings set back to provide many different floor plates. 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 disrupting the flow of the wind over the height of the building.
If you want to build high, you must first dig deep, driving foundations down well below the surface. The tower's superstructure is supported by a large reinforced concrete mat, which is in turn supported by 192 bored reinforced concrete piles.
The mat is 3.7m thick, and was constructed in four separate pours totaling 12,500 cubic metres (m³) of concrete. Bauer Spezialtiefbau, with Middle East Foundations, took on much of the piling work, which required bores to be sunk for cast in-situ piles, to a depth of 43 metres.
Known by some as the ‘Rolls-Royce' of the drill rig world, the Bauer BG40 can deliver, as the name suggests, 40nm of torque. Of course, there isn't a situation that we could imagine where you would need such heavy power for drilling piling holes - half of this would be sufficient for most situations. However, a reserve of torque means there is less stress put on the machine, so it can get on with what it is required to do.
Around 45,000m³ of concrete, weighing more than 110,000 tonnes, were poured for the foundations - that's equivalent to 18 Olympic sized swimming pools - with 192 piles running to a depth of over 50m.
A high density, low permeability concrete was used in the foundations, as well as a cathodic protection system under the mat. This is an effort to counter the effects of the highly-corrosive ground water.
Bores for the 192 deep piles were sunk in 2004. Each of them was designed to be cast in situ, and as such needed to be very deep. Ground conditions at the Burj site were favourable - the soft, but not unstable, soil proved easy to dig into. Other sites in the region are not so fortunate - naturally occurring limestone requires breaking with a breaker attachment first.
Concrete and steel
You know already that over 45,000m³ of concrete was used to in construction of the tower's foundations. The overall construction process will have used 330,000 m³ of concrete and 39,000 tonnes (43,000 ST; 38,000 LT) of steel rebar. Laid end to end, the rebar used in the tower would extend over a quarter of the way around the world. For the construction of the tower, BASF developed a special concrete mix that was pumped to a height of more than 600 metres without segregating. Thanks to BASF's admixture Glenium Sky 504, the concrete could be worked on for more than three hours before hardening took place. This allowed for a shorter construction time and gives the building a longer useful life, making it more sustainable.
In November, 2007, the highest reinforced concrete corewalls were made using concrete pumped from ground level to a vertical height of 601 metres. This broke the previous pumping record for a building of 470m on the Taipei 101 and the previous overall world record for vertical pumping of 532 metres for an extension to the Riva del Garda Hydroelectric Power Plant in 1994. The concrete pressure during pumping to this level was nearly 200 bars.
When the record was set, a photocall was arranged and a distance of 601 metres was reported as the new record. However, it was discovered shortly afterwards that the concrete needed to go a little further and so an extension was added to move the concrete to 606 metres.
The mix was able to reach such astounding heights by running through a high-pressure trailer mounted pump (a Putzmeister 14000 SHP D). The concrete required approximately 40 minutes from the filling of the hopper to its discharge from the delivery line. The concrete volume in the line amounted to approximately 11m³ with this installation height - meaning there was roughly 26 tonnes on the pump after every piston stroke - or five big elephants.
Over a period of about 32 months, the high pressure pump and two others delivered more than 165,000m³ of high-strength concrete, which, using our preferred unit of measurement, is about 66 Olympic sized swimming pools.
Exterior cladding of Burj Khalifa began in May 2007 and was completed in September 2009. At the initial stage of installation, the team progressed at the rate of about 20 to 30 panels per day and eventually achieved as many as 175 panels per day. Burj Khalifa has set a new world record for the highest installation of an aluminium and glass facade, at 512 metres.
The total weight of aluminium used on Burj Khalifa is equivalent to that of five A380 aircraft and the total length of stainless steel bull nose fins is 293 times the height of Eiffel Tower in Paris.
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 the tower.
Over 300 cladding specialists from China were brought in to do the work. 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.
They're graceful, mysterious and it seemed for a time everybody's favourite topic. The high level cranes at the Burj were always enigmatic, enshrouding the operator of the very highest unit in mystery. There were stories circulating about ‘the Indian on top of the world' which speculated that he was paid a king's ransom, and that he had been made an honorary UAE citizen.
All of this was really nothing more than idle gossip - the figure had become more of a mystery man through Emaar 's refusal to let the media have any access to him, though this was most likely due to the developer keeping the exact height of the structure a closely guarded secret - a figure which the high-level operators undoubtedly knew. Despite this conundrum, there is quite a lot that we do know about the high-level cranes. For a start, there was not one, but three Favelle Favco cranes that served right up to level 156.
Given that the machines worked 24 hours for much of the project's duration it would be safe to assume that there was a team of at least nine drivers and many other technicians to ensure safe operation. (In fact, Emaar recently confirmed that a 35-strong workforce were on hand to run the cranes, though this is a drop in the ocean compared to the total of 12,000 employees on the project.)
Usually, the cranes' loads consisted of steel reinforcement beams, but welding equipment, scaffolding, gensets and even tanks of fuel for the diesel powered cranes all needed to be lifted to the correct floor.
Installing the three high-level cranes was relatively straightforward as sections of the cranes could be moved up the tower with the completion of new levels.
Getting the towers down however, required a little more lateral thinking. The first high-level crane was moved in November 2007 down to level 99 in order to serve as a future recovery crane. The next high-level crane came down in October 2008, leaving one prominent machine apparently stuck at the top, while people on the ground speculated how it might come down.
The answer was that another small crane had to be lifted to floor 159. With a crane on this floor as well as the one on level 99, the dismantling process was ready to begin. The process started with the crane climbing down from its working height of over 700 metres. The crane removed its own mast sections and lowered them to the ground until the boom and power pack were at the position of the Level 159 recovery crane.
From there, the Level 159 recovery crane dismantled the remainder of the main crane, lowering the pieces of boom, mast and power pack to the recovery crane at Level 99, which further lowered them to the ground.
The dismantling of the cranes at Burj Khalifa was indeed a finely orchestrated set piece - except that the artists here were huge machines.
The three cranes on the tower were all diesel Favelle Favco units, of various specifications. This type of diesel-hydraulic crane is popular on ‘supertall' skyscrapers, due to a useful turn of speed and power. However, one of the main challenges was actually getting the fuel to the required height - there are no petrol stations on the 159th floor.
Burj Khalifa was an international collaboration between more than 60 contracting and consulting companies from all over the world. At the peak of construction, over 12,000 workers and contractors were on site every day, representing more than 100 nationalities. According to Emaar , construction will have taken 22 million man hours.
Fire safety and speed of evacuation were prime factors in the design of Burj Khalifa. Concrete surrounds all stairwells and the building service and fireman's elevator will have a capacity of 5500kg and will be the world's tallest service elevator. Since people can't reasonably be expected to walk down 160 floors, there are pressurised, air-conditioned refuge areas located approximately every 25 floors.
The mechanical, electrical and plumbing services for Burj Khalifa were developed in co-ordination during the design phase with the co-operation of the architect, structural engineer and other consultants. Hyder Consulting was appointed as a supervision consultant with responsibility for overseeing execution of the MEP. An ETA-Hitachi-Voltas joint venture was awarded the building's MEP contract.
Seven double-storey mechanical floors house the equipment that bring Burj Khalifa to life. Distributed around every 30 storeys, the mechanical floors house the electrical sub-stations, water tanks, pumps and air handling units that are essential for the running of the building.
These mechanical areas typically serve the 15 floors above and below them. The primary distribution route for services is through the main risers within the central core of the structure, which remains the same size to level 150 despite the overall building shape tapering with height. MEP operations are managed by a central BMS, with local control panels in each plant room, all connected by fibre-optic cabling. During construction, deliveries of MEP equipment tended to be made during the night, with the podium and basement used as storage space. Cranes, hoists and service lifts were used to transport the various materials.
The Burj Khalifa's water system supplies an average of 946,000 litres (250,000 gallons) of water daily. At peak cooling, Burj Khalifa will require about 10,000 tonnes of cooling, equal to the cooling capacity provided by about 10,000 tonnes of melting ice.
Dubai's hot, humid climate combined with the building's cooling requirements creates a significant amount of condensation. This water is collected and drained in a separate piping system to a holding tank in the basement car park.
The condensate collection system provides about 15 million gallons of supplement water per year, equal to about 20 Olympic-sized swimming pools. This water is to be redirected to the gardens surrounding the tower.
The tower's peak electrical demand will be an estimated 36mW, equal to about 360,000 100 Watt bulbs operating simultaneously. According to one report, the tower has more than one hundred thousand light fittings, 375km of fire alarm cabling and 34km of chilled water pipes.
Elevators & Lifts
Burj Khalifa will be home to 57 elevators and eight escalators. The building service/fireman's elevator will have a capacity of 5500kg and will be the world's tallest service elevator.
The Burj Khalifa features distinct sections: residential apartments, serviced apartments and hotel rooms, and corporate offices. Elevators have been arranged in zones to serve these different audiences, with what is known as a ‘sky lobby' system.
The sky lobby is an intermediate floor where residents, guests and executives will change from an express elevator to a local elevator, which stops at every floor within a certain segment of the building. Burj Khalifa's sky lobbies are located on level 43, 76 and 123 and will include a lounge area and kiosk, amongst other amenities.
All elevators have been supplied and installed by Otis. No elevators are installed to travel all 160 floors of Burj Khalifa. Instead, they are grouped to align with the floor layout, offering passengers a direct express service to their destination by bypassing other floors.
The main service elevator, positioned in the central core of Burj Khalifa, has the world's highest elevator rise at 504 metres - more than the height of Taipei 101 in Taiwan (448 metres). It travels at nine metres per second and also has the world's longest travelling distance for an elevator. Another service lift in the spire has the world's highest landing point at 636.9 metres.
Double-deck elevators, with built-in light and entertainment features including LCD displays, will exclusively serve visitors to At The Top, Burj Khalifa, the world's highest outdoor observation deck situated on level 124, as well as office users transferring at the sky lobby at level 123.
These double-deck units - used for the first time in the Middle East by Otis - are the highest rising double-deck elevators in the world and will travel at the speed of 10 metres per second. They have a capacity of 12 to 14 people per cab.
Podium and access
The podium provides a base anchoring the tower to the ground, allowing 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. The number of underground car parking spaces is reported to be 3000, which suggests that the owners are keen for people to use the nearby metro station and downtown light railway for access.
At the foot of the mighty Burj sits the ‘The Park', an 11 hectare expanse of gardens, trees and water features. What is perhaps most noteworthy about The Park is that is irrigated using a water collection system that recovers the condensation from the tower's cooling equipment. This provides the park with around 15 million gallons of water a year - or enough to fill 20 Olympic-sized swimming pools. The Park was designed by SOM, designer of the tower itself, and SWA Group of California. WET, the designers of The Dubai Fountain, developed the park's six water features.
The interior design of Burj Khalifa's public areas was done by the Chicago office of Skidmore, Owings & Merrill LLP and was led by award-winning designer Nada Andric. It features glass, stainless steel and polished dark stones, together with silver travertine flooring, Venetian stucco walls, handmade rugs and stone flooring. Over 1000 pieces of art from prominent Middle Eastern and international artists will adorn Burj Khalifa and the surrounding Emaar Boulevard. Many of the pieces were specially commissioned by Emaar .
The two main contractors for the interior fitout were DEPA and Fino International.
At one point, interior contracting specialist DEPA famously told Arabian Business magazine that the job of fitting out the tower was a ‘nightmare'. The company won a US $600 million contact to oversee the fit-out of nearly 1000 residential and serviced apartments as well as corridors and lift lobbies. Despite the challenges of moving men and materials up to as high as the 100th floor, the company got the job done in reasonable time.
The crowning glory of Burj Khalifa is its telescopic spire comprised of more than 4000 tons of structural steel. The spire was constructed from inside the building and jacked to its full height of over 200 metres (700 feet) using a hydraulic pump.
In addition to securing theBurj Khalifa's place as the world's tallest structure, the spire is integral to the overall design, creating a sense of completion for the landmark. The spire also houses communications equipment.
The top four floors of the Burj have been reserved for communications and broadcasting. These floors occupy the levels just below the spire.
Access for the tower's exterior for both window washing and façade maintenance is provided by 18 permanently installed track and fixed telescopic, cradle equipped, building maintenance units. The track mounted units are stored in garages, within the structure, and are not visible when not in use.
The manned cradles are capable of accessing the entire facade from tower top down to level seven. The building maintenance units' jib arms, when fully extended, will have a maximum reach of 36 metres with an overall length of approximately 45 metres.
When fully retracted to parked position, the jib arm length will measure approximately 15 metres. Under normal conditions, with all building maintenance units in operation, it will take three to four months to clean the entire exterior facade.
FANTASTIC ACHIEVEMENT, but why on earth the fantastic venturi effects of the tower's height (inner service core) was not put into good use for driving wind turbines (suction or pressure) to generate electricity; as well as the piston action of lift cars going up and down ??.. I am convinced that would have provided a healthy back up to 30mW+ power requirement of the building, including reducing ventilation and lighting power requirements.. Has someone left out the humble calculator during design ? In any event, hats off to design and construction teams; well done indeed. Hal-Luke Savas MBA FCIM MBIFM ICIOB affCIBSE firstname.lastname@example.org