Rising desert bloom

In Dubai size matters and everything about Dubai—based Emaar Properties’ Burj Dubai Tower is big. Greg Sang, Emaar's senior manager, projects, told IC that at the peak of construction activity, for example, more than 20000 construction workers will be on the AED 73 billion (US$ 20 billion) Downtown Dubai site, with 4000 working on the tower alone.

When complete Downtown Dubai will provide 4.2 million m² of living space on 203 ha of land, making it the world's biggest construction site, with the world's tallest building as its centrepiece.

Planning for the AED 11.75 billion (US$ 3.2 billion) Burj began when US—based architects Skidmore, Owings &Merrill (SOM) won a design competition in early 2003. According to SOM architect Adrian Smith, who also designed

Shanghai's 420 m Jin Mao tower, its design is derived from the geometries of the desert flower and the patterning systems embodied in Islamic architecture.

The tower is composed of three elements arranged around a central core. As it rises from the desert it tapers in an upward spiralling pattern. At the top the central core emerges as a spire.

Foundation construction

The main contractor at the Burj is a joint venture (JV) comprising Samsung Corporation from South Korea, Besix from Belgium, and locally based Arabtec. US—based Turner Construction International is managing the tower's construction, while Hyder Consulting Middle East is the main consultant.

Awarded the contract in December 2004, the JV started on site in January 2005. Its AED 3.12 billion (US$ 850) million contract will see the Burj rise to a minimum of 800 m over a 47 month construction period with completion due in November 2008.

A 575 m high concrete core will contain about 160 storeys covering 495000 m².

A steel superstructure tied to the core will take the Burj to whatever height is ultimately needed to take the world's tallest building crown. Above the core it will house only lifts, services and the spire.

Emaar Properties, and indeed all those connected with the project, is reluctant to give away too much technical detail. During IC's visit several questions concerning construction techniques, final cost and height were met with a polite but firm, “no comment”.

However, foundation work for the Burj was completed in March this year after 12 months, at a cost of AED 54 million (US$ 15 million). According to Hyder Consulting's project director, Derek J Kemp, it involved some “critical measures” that were taken to ensure the tower sits on a strong steel and concrete podium.

Middle East Foundations and Bauer installed the tower's piles. The first task was to carry out a series of large-scale pile load tests, followed by the installation of 200, 1.5 m diameter piles to a maximum depth of 50 m and 650, 900 mm diameter piles to a maximum depth of 36 m. These are bound together by a 3.7 m thick concrete raft across 8000 m², encompassing the tower's entire footprint, which was completed by Nasa Multiplex.

Nearly 18000 m³ of concrete was poured for the tower piles while 15000 m³ of concrete was used for the podium piles. In addition, the raft comprises 12300 m³ of concrete, bringing the total concrete poured into the foundation to over 45000 m³, with a weight of more than 110000 tonnes.

Above ground

During the searing heat (46°C, 70%—plus humidity) of IC's visit, the beginnings of the concrete core were clearly visible, rising about 30 m above ground. Construction started in March using a formwork concept developed by Austria—based Doka and the JV, using Doka's SKE 100 climbing system and Top 50 wall formwork system.

Often varying from one floor to the next, the complicated ground plan of the building is one of the key formwork engineering challenges in the construction of the shaft core and walls of the three wings of the building, according to Martin Hoerlesberger, Doka's key account manager for the Middle East.

“No fewer than 180 pouring and climbing steps will be required before the reinforced—concrete construction can be completed. For each of these sections, around 5000 m² of Top 50 wall formwork will need to be raised hydraulically, by 227 automatic climbers,” he said.

World class team

Emaar has assembled a “world class team”of contractors and consultants to bring the Burj to life. These include Emaar's Greg Sang, who has worked on high—rise projects in Hong Kong, and Hyder Consulting's Derek Kemp, who previously worked on several high—rise projects in Saudi Arabia.

During the design process, according to Mr Kemp, Hyder had to consider a plethora of constraints, including people traffic through the building (lift technology), wind speeds and the affect of the wind pattern on surrounding buildings, reflectivity, radar shadowing and flight path interference.

Mr Kemp told IC that Hyder's duties mean it is the architect of record, which involves making all the necessary submissions to the Dubai Municipality to obtain approvals for construction. It also provides site supervision services, with an on—site team responsible for the approval of all contractors’ construction shop drawing submissions, responding to contractors’ information questions, and inspecting the works to ensure they are carried out in accordance with the approved drawings and specifications.

“We also have a separate site based team who are responsible for reviewing and checking the SOM design for structure, architecture, and mechanical and electrical services to the extent that we confirm to the client that we adopt the design and take full responsibility for it,” said Mr Kemp. “This ‘design adoption’ is something I've never come across before, however, it's the clients way of making sure everyone has some responsibility in the project, which I ultimately think is a good thing.”

Mr Kemp was also keen to stress that the main drivers towards successful delivery of the project so far have been the “first class”planning by the contractors, plus the “world class”design team assembled by the client.

Part of that team is high—rise ‘guru’ Dr

Andy Davids, director of structures, Burj Dubai Tower. Dr Davids is head of Hyder Consulting's Sydney, Australia office. According to Mr Kemp, this is Hyder's “high—rise centre of excellence”.

Dr Davids has worked on many iconic tall structures, including “The Latitude”in Sydney (see IC May 2004).

To describe Dr Davids as an engineering enthusiast would be a bit of an understatement. During a very animated chat at the Burj site offices he told IC that, “As an engineer this is the Holy Grail of engineering, you dream about a project like this; the tallest building, the longest bridge etc.

“No—one's ever done anything like this before — it's the tallest man—made object and presents some hard and soft challenges. By hard I mean it's a “never been done before”project, and by soft I mean managing the people, the logistics. Success ultimately rides on how smart you can be on the logistics side; planning, getting people through the building, material delivery, timing etc,” he added.

“The formwork concept envisages climbing—steps being taken independently of one another in six separate zones, with work on the wing walls preceding two to three storeys behind the central shaft core. ‘De—linking’ the in—situ pouring operations from one another in this way — by dividing up the work into six mutually independent zones — makes it possible to construct a ‘typical’ storey in a three—day cycle,” added Mr Hoerlesberger.

The automatic climbing formwork, which will be used to form 154 storeys, is designed to withstand wind speeds of over 200 km/hour, and is completely enclosed in a steel grille to provide the greatest possible safety for the crew as they precede skywards. It also raises the four concrete placing booms — each up to 32 m long — from one floor to the next, independently of the site's tower cranes.

Concrete core

Sub—contractor Universal Concrete Products (Unimix) is handling concrete placing and pumping on the core. The company is using two Putzmeister BSA 14.000 SHP stationary pumps, which operate at over 300 bar and have an output in excess of 70 m³/hour. UNIMIX expects to supply, pump and place about 250000 m³ of concrete during its contract.

According to E.R. Menon, technical director of Unimix, “The production of high—quality concrete is a science. Our skilled concrete technicians are continuously developing mixture breakdowns: concrete with 100 N/mm² compressive strength, self—compressed concrete with low heat of hydration and also concrete types of high strength with equally high elasticity, for example.

Mr Menon said that several of these concrete mixtures could be used during construction of the Burj. However, like many of those connected to the project he was unwilling to provide any specific technical details.

Moving materials around the site to service the pumps, men and other equipment is a web of tower cranes. At the time of IC's visit there were seven tower cranes at work on the podium and three on the tower. The three on the tower are all Favco cranes, including an M 440 D, an M 380 D and an M 220 D. All three have a boom length of 55 m and a hook height of 48 m. Maximum radii are either 52.5, or 53 m.

Maximum lifting capacity for the M 440 D and M 380 D is 25 tonnes at 23 and 18 m respectively, while the M 220 D has a maximum lifting capacity of 11 tonnes at 24 m. Maximum capacity for the M 440 D is 8 tonnes at 52.5 m, the M 380 D's maximum capacity is 5.3 tonnes at 53 m, while for the M 220 D it is 3 tonnes at 52.5 m.

The seven tower cranes on the podium started arriving on site in April. Six are Potain and one is a Favco. The Favco is an M 220 D with a 65 m luffing jib and a maximum lifting capacity of 16 tonnes. The six Potain tower cranes include four MC 235 Bs (55 m boom, maximum capacity 10 tonnes), and two MC 310 K12s (65 and 70 m booms respectively, maximum capacity on both is 12 tonnes).

Health & safety

A project of such magnitude and daring means the world is watching very closely, said Mr Sang, “Our health and safety division is determined to make construction of the tower a showcase for the rest of the world.”

The job of site safety falls to Mohamid Moizuddin, health and safety manager for the JV. “With about 1700 men currently on site the client is very keen on health and safety, and on 7 July we passed 1 million man hours worked without an injury,” he said. With so many workers on site, and so many different nationalities and cultures, including Indian, Pakistani and Sri Lankan, Mr Moizuddin admited there could have been some serious problems, not least actually communicating with the workforce. However, the majority of workers speak Hindi and those that do not have any tasks translated for them.

The AED 11.75 billion (US$ 3.2 billion) Burj Dubai Tower is the centrepiece of the AED 73 billion (US$ 20 billion) Downtown Dubai site, which will provide 4.2 million m2 of living space on 203 ha of land.

Working conditions are also top of the agenda with shelters, water stops, medical checks and a three—hour health and safety induction for anyone coming on site. Three different site entrances mean man, machine and materials only meet during the construction process.

Dubai's Government has also recently introduced a four—hour daytime working break. With temperatures approaching 50°C it was decided that all outside work should stop between 12.30 and 4.30 pm. Workers also get three breaks per shift, receive the World Health Organisation recommended daily water intake and have access to 24—hour on site medical care, while a helipad can be used to get any seriously injured person to the nearest hospital.

However, there is also the risk of a terrorist attack to contend with and Mr Moizuddin told IC there is high security throughout the site in respect of preventing a terrorist attack. “We have an action plan in place to cope with every possible emergency,” said Mr Moizuddin.