Contractors are battling the odds to bring the world’s tallest building in on time. Mark Hansford reports from the Burj Dubai.
Dubai is a crazy, crazy place. Everything is big and brash from the vast man-made Palm islands and the staggering Vegas-style recreation of the Seven Modern Wonders of the World, to the 10 skyscrapers in excess of 100 storeys set to be completed this year.
On the flipside, creating this Vegas-meets-Manhattan vision are 250,000 foreign labourers, many of whom live in conditions described by Human Rights Watch as being “less than human”. Indeed 35,000 of them only last week returned to work on the Burj Dubai megatower after a two week strike over pay and conditions.
Put in this context the 800m-plus tall Burj Dubai tower is perhaps nothing extraordinary. But that is to seriously downplay the challenges being faced. Workers are unskilled and don’t speak English or Arabic.
Materials are being shipped from around the globe and delivered to a site which – incredibly – has no room for storage. The cladding contractor went bust in February last year. The concrete floors have sagged and have had to be beefed up.
Temperatures often exceed 50°C. And the client has even now, with concrete pours complete, still not yet confirmed its final height, although the drawings hanging in the site office last week put it at 808m.
The tower is being built for developer Emaar Properties by South Korean company Samsung. Skidmore, Owings & Merrill (SOM) of Chicago leads the architectural, structural engineering and mechanical engineering design team.
Hyder Consulting is the client’s engineer and Turner International, the project manager. The total budget is set at around 500M. Work began on site on 1 February 2005.
The structural shell of the Burj is already the tallest building on the planet (see box). Last week nce.co.uk broke the news that in-situ
concreting works on the structural core were successfully completed at a height of 601m.
Constructing this involved an unusually high proportion of wall-forming operations for a skyscraper. Its honeycombed design meant forming 430,000m² of walls – twice the area of the floor-slabs. A typical storey was finished every three days.
Doka provided the formwork, and its system proved exceptionally robust.
“As the in-situ concrete core was being built ahead of the floor-slabs, construction progress on the whole building was entirely dependent on the self-climbing Doka formwork solution,” says Samsung’s project director Kyung-Jun Kim.
“The system functioned with machine-like precision, allowing us to complete the in-situ concrete core within the original timetable.”
Climatic conditions encountered at the site were often extreme: the desert climate next to the open sea causes great temperature fluctuations between day and night, and this can lead to violent sandstorms with wind speeds of over 100 km/h.
Conditions such as these tested men and materials to the limits, which makes the safety record to date all the more impressive.
So far 29,333,100 manhours have been worked with just three reported lost time injuries.
The biggest drama of the project to date was in March when news leaked out that carbon fibre reinforcement was being used to strengthen defective floor slabs (NCE 29 March). Emaar denied at the time that there were any strength issues but it is widely reported that the floor slabs were designed as prestressed but in fact poured as simply reinforced. As a result they were too shallow and light on reinforcement, with the result that there was excessive sagging.
In total, floors five to 15 have now been beefed up with a combination of carbon fibre strips and blue steel I-beams.
But that is in the past and attention is now focused on erecting the final 200m tall steel spire and, more importantly for the programme, the aluminium and glass cladding.
Cladding work got off to a terrible start when joint venture cladding contractor Schmidlin collapsed February last year, weeks before erection was due to start, leaving joint venture partner Arabian Aluminium utterly in the lurch.
“We trawled the world looking for someone to replace Schmidlin,” says Arabian Aluminium project director John Zerafa. “We lost 13 months before we signed up Far East Aluminium and have broken quite a few records getting back on track. We are endeavouring to finish on time – the original time – at the end 2008.
“Between 10 May and now we have clad 50 levels. Most of the work is done in China, with the cladding coming in pieces and assembled on site with local glass.
“We are doing 100 panels a day – both making them in the factory and assembling and installing them. At any one time I’ve got up to 30, 40ft containers en route to and from China.”
Installing the glazing is also going to be a major feat and again, safety is paramount.
“Safety is very stringent here,” says Zerafa.
“There are 9,000 people on the job at the moment and our activity is on the perimeter – maximum high risk,” he says.
Zerafa’s men work from safety harnesses attached to safety rails his team has engineered itself.
“It’s for my piece of mind. You can’t put a value to safety and you can’t afford to lose your reputation for the sake of saving a dollar.”
The glazing panels, up to 6.4m tall, are hung off 25,000 Halfen cast-in fixings and slot together with no need for extra sealant. Because the Burj tower has a curved exterior, there is no tolerance for installation or construction errors.
“On square buildings you always lose 10mm in the corner. Curved buildings are 30 times more difficult”, says Zerafa.
Fire safety on the Burj was always going to be a top priority. The building has been designed to evacuate 35,000 people, more than twice its expected occupancy. Evacuation is by stairs, and it’s a long way down from 160 storeys – so pressurised air-conditioned refuge areas are being installed every 25 floors for evacuees to rest or await rescue.
To keep fires contained, exacting US standards are being employed, with Hilti firestops being used to plug the notoriously dangerous gaps between floor slabs and external cladding because the building is curved, and gaps can be “quite large” – up to 150mm says Zerafa.
Mineral wool 150mm thick is being used to plug the gap. It is held in place by Hilti’s CP672 sprayable fire-rated mastic, designed for joints with maximum movement.
Cladding is a seriously critical path activity, because only when a floor is clad can air conditioning be blasted through it and fit out begin . And on the Burj, even fit-out is a massive construction management exercise. Depa Dubai, the interior contractor responsible for fitting out the Burj’s 899 luxury apartments, has as its project director a Hong Kong airport veteran in Bob Dixon.
A RECORD BREAKER… BUT FOR HOW LONG?
When completed, Dubai’s landmark tower will be the tallest structure in the world in all four of the criteria listed by the Council on Tall Buildings & Urban Habitat (CTBUH) - height to the structural top, the highest occupied floor, height to the top of the roof, and to the tip of the spire, pinnacle, antenna, mast or flag pole.
Burj Dubai is billed to scale past the KVLY/KTHI television mast in Blanchard, North Dakota, which at 628.8m is the world’s tallest mast and technically qualifies to be the world’s tallest structure, even though it is stabilized with a series of guy-wires.
But several other major projects in the region are already threatening to topple the Burj.
Kuwait has approved a plan to construct the 1,001m tall Burj Mubarak Al-Kabir tower, part of the Ł43bn Madinat Al-Hareer project that will include not only the skyscraper but an airport and a bridge linking Madinat with Kuwait City, which sits across a bay.
And just down the road from the Burj on Palm Jumeirah, Emaar’s chief rival Al Nakheel is planning a gazumping on a grand scale with Al Burj, a tower set to top 1,050m and possibly reach 1,200m.
But both of these pale into insignificance when you look across the border to Saudi - where plans have been unveiled for a 1.6km-high whopper.