Reaching for the sky
The Burj Dubai is already one of the city's biggest landmarks and set to be the tallest building in the world, its construction is being eagerly watched. Alison Luke finds out how MEP services will meet the challenge of the spiralling tower.
Billed as the tallest building in the world, the task of providing services to the Burj Dubai was always going to be a challenge. The world records made by the project stretch to the services themselves, with the longest lift run in the world being among them, despite this, the aim of providing constant services is involving the use of proven technologies and close logistics.
MEP senior manager of Samsung-Besix-Arabtec joint venture, Rachid Ghamraoui explains: “One thing that is very important in this project is that we are using proven design enhanced to suit the project needs from the height and configuration of the building.” This decision to opt for up-to-date technology comes from the need to ensure constant operation of services in all foreseeable eventualities.
“All [MEP] equipment has been checked and calculations made for anti-seismic, anti-vibration and to take into account the deflection and the movement of the building,” explains Ghamraoui.
Due for completion in December 2008, the Burj Tower is already one of the tallest in the Middle East, currently standing at over 100 storeys. The final structure will be over 160 storeys tall, with a floor area of 465,000m2 and will include an Armani-designed hotel, residential apartments, boutique offices and commercial spaces.
Its shape is based on an indigenous desert flower, with three distinct wings protruding from a central core that stretches the full height of the building, the wings gradually decreasing with height creating a spiral effect.
Chigaco-based architect SOM designed the building for client Emaar, with Turner Construction acting as project manager. The main contractor’s role on the project is being undertaken by an integrated joint venture between Besix, Samsung and Arabtec.
The major MEP works for the permanent installation is being carried out by ETA, Voltas and Hitachi under a joint venture contract, with several client-nominated subcontactors carrying out other packages, such as the extra low voltage system by Johnson Controls.
The scale of build and three-day per floor speed of construction has meant that the close co-ordination between contractors plays a major role in the project and all have been site-based from the start of construction. “The logistics will be a very, very important issue here,” stresses Ghamraoui. In addition to ensuring materials and labour can reach the correct height when needed, the tight space around the tower must also be considered.
“Very soon the external works comprising of irrigation, landscaping and special water features will commence, which will further limit the available space,” explains Ghamraoui. “We have to organise ourselves in order to store the material at site in a proper way or to get it stored outside and move it to the building at the right time to get it directly to the right locations,” he adds.
The heart of the building from the mechanical services viewpoint is at level B2, which feeds a main riser in the central core, and in turn, sub-risers in the building’s wings. Chilled water is supplied to the building from a district cooling plant that also serves the adjacent Dubai Mall and Lake Tower Hotel.
The supply of chilled water to the tower is carried out by a forced pump system. The primary chilled water is received from the EMAAR district cooling plant at 3.3°C at level B2. It is then passed through a series of heat exchangers before being pumped to a plantroom at level 17, and thereafter to further plantrooms at levels 40, 73, 109 and 139. “The water is then distributed from the respective plantrooms to air handling units and fan coil units located in apartments and guestrooms” explains Ghamraoui.
The domestic water supply and fire sprinkler system work under the principle of gravity, with water being pumped to the water tanks in the upper level mechanical rooms for further distribution.
“This whole concept is almost like an umbrella – you provide at one location and then distribute downwards. This is a unique concept and is achievable merely due to the available gravity from the very high height of the building,” Ghamraoui adds.
“One thing that was very important [to the MEP distribution] was the structure of the building,” stresses Ghamraoui. “With the huge thickness of walls, from a builders’ work point of view, we had a challenge not to miss any of the holes or openings.” This meant the early involvement of the MEP contractors was vital, as was their co-ordination with the civils contractors.
The length of pipe runs through the main riser also meant that the system design had to consider the movement of the building as well as natural expansion and contraction of both the pipes and building structure. A specialist subcontractor was appointed under the MEP scope of works to study the pipe movements and advise on the positioning of expansion joints and guides. “For every single pipe we made a calculation for the vertical part, every angle and deviation,” stresses Ghamraoui.
Rather than a conventional gravity support system, pipe guides and ball joints are installed at various storeys, thus enabling free movement of the pipework within the building taking into account seismic, building deflection, vibrations and acoustic requirements. This design means that a single stanchion at the base of the system supports the weight of the water and pipework. With a load of 140 tonnes at this point, careful design was needed. “The elbow [at the base] is a very special piece…the thickness is much higher than any elbow normally used and it is of a higher grade of steel,” explains Ghamraoui.
With an 84MVA total capacity to meet, supplying electrical power to the Burj has meant an unusual system being applied. Rather than step-down transformers reducing the power voltage at the hv incoming supply, here an 11kV power supply is distributed throughout the building via the main riser. This is reduced to a 400V supply at substations located throughout the building, then distributed by busbar via sub-mains distribution boards, which finally feed local distribution boards via corridor routes. A four-core, 180mm2 diameter cable was chosen for the hv distribution as the flexibility of tap-off points given by busbar was not required.
To ensure total security of supply there are two main electrical risers located in the building core – one for standard and the other for emergency power – that operate in parallel. Five 2200kVA generators provide further back-up to the life safety systems in the event of a total power failure.
Not surprisingly with the tower design of the building, vertical transportation is a major factor in the MEP services. A total of 54 elevators and eight escalators are being installed under a subcontract package awarded to manufacturer Otis.
Included within this design is the longest lift tunnel in the world, which will see a double-deck lift run from the ground to a visitor’s area at levels 122 and 123 that will house restaurants, bars and an observatory deck. This is also one of the fastest double-deck lifts in design and will operate at a speed of 10m/s. “This was specially developed in order to cope with the amount of people that are likely to want to visit this iconic building,” explains Ghamraoui. “In a double-deck you can put more people in a limited space.”
Fire lifts with speeds of 9m/s will serve all floors of the building. Access to higher floors via the general elevators, as is standard for towers, requires users to transfer between two or more lifts to reach their destination; speeds for these lifts range from 1.75-7m/s.
The positioning of major MEP plant at height required careful planning due to the construction methods being used and the future replacement of plant. “The construction of the tower is something special from the civils point of view,” states Ghamraoui, “The whole building is under jump form, there is shuttering everywhere, so if we want to introduce equipment we cannot do it from the top.
“Some of the equipment weighs over 10-15 tonnes, therefore loading platforms capable of receiving this weight will be installed at various plantroom levels projected outside of the building,” he adds.
To enable the speed of structural construction to continue unhindered, the MEP contractor has opted to crane in large-scale pipes from the top of the building directly into the central core.
“We are installing chilled water pipe that is 600mm diameter and 12m in length, the weight is around 3500kg in one piece,” explains Ghamraoui, “We found a way to make an opening within the jumping form in order to introduce those huge pipes and minimise the welding joint numbers on site; it’s a very special method using intermediate hoists inside the tower.”
Removal of the plant at the end of its lifespan has also been considered. Plantrooms are located adjacent to the service lifts, with the elevators sized to cater for the largest sized section of plant that must be removed – the transformers. “It has also been looked at from a layout point of view: the routing from the plantroom to the elevator is free of any equipment, so we don’t have to stop operating any installation, you just dismantle the plant and get it replaced,” stresses Ghamraoui.
To get the quantities of materials supplied for the project was a task in it itself, with over 4,000 fan coil units alone (see box ‘Burj Dubai: the figures’). “That was one of our achievements – we can say today for this project that almost 95% of the materials are already approved and orders are in place,” says Ghamraoui.
“One thing that is very important in such a huge project is the team spirit. If everyone does not look to the same targets in a positive spirit we cannot achieve this project. But I can say with certainty this spirit is there,” he concludes.