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Sat 28 Oct 2006 04:00 AM

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Tuning workers in to 70 floor-cycles

Building super-tall structures doesn’t just carry logistical and structural challenges, a well-trained labour force is also essential for site safety. Christopher Sell reports on the progress of the 290m Emirates Crown Tower, and the working practices of ASGC.

Building super-tall structures doesn’t just carry logistical and structural challenges, a well-trained labour force is also essential for site safety.Christopher Sellreports on the progress of the 290m Emirates Crown Tower, and the working practices of ASGC.

With safety in mind, ASGC is working with the same set of labourers for the entire project. According to the contractor, the workers become used to the floor cycles, and when working at height, this familiarity reduces the risk of accidents.

In a city where each day seemingly brings with it another high-rise development or gleaming citadel emerging from the sand, it is becoming increasingly difficult to get noticed if you are a developer. Forty-storey towers don’t cut it anymore; if you want to be noticed, aim really high.

Dubai Marina features a plethora of towers all vying to dominate the landscape, hence buildings with a bit of personality stand out. Along the Beach Road and across from the Dubai International Marine Club, the 70-storey, 290m Emirates Crown tower, geared towards a multicultural, family-orientated community, is aiming to do just that. ASGC is the contractor and developer and DAR is the consultant.

With a range of unique attributes contributing to a swift construction, the Emirates Crown Tower is just one year away from completion, with a build cycle that has become more efficient as the tower has progressed.

“We have perfected it because we have done so many floors now,” says Bishoy Azmy, deputy general manager, ASGC. “Now we are working to a five-day cycle, before we were on 10 days, so it has been halved. And it has only been a year since the excavation started.”

The speed of the construction is primarily the result of employing a hydraulic climbing system. This allows the core to be built a few days ahead of laying the slabs.

At the time of visit, work was proceeding on the 35th floor for the core, while labourers were concerning themselves with the slabs for the 32nd. Allied to this, aluminium formwork is used before hollow core slabs (a prefabricated slab or prestressed concrete), measuring 12m by 120cm are brought in. A crane is used to lift the precast slabs in position before steel mesh and 7cm of scree is then cast on top.

“It is quite a laborious procedure as it has so many phases, but we have perfected it as we have done so many floors now,” says Azmy. “Not a lot of contractors use scree and definitely not a lot use hollow core in the tower. It is still a new approach,” explains Asem Karas, construction manager, ASGC, before outlining the simple efficiency of the five-day floor cycle.

“On day one we cast one half of the column, on the second we cast the second part of the column while starting the formwork for the first part. The third day we are completing the formwork of the beam and the casting moves onto the second part. By the fourth day we are placing the hollow core slabs down onto the first half, then by the fifth we are completing the hollow core slabs for the second half and casting and topping the first,” he says.

Azmy acknowledges that the use of aluminium has budget implications but stresses this is offset by the benefits. “Aluminium is expensive but it makes the construction much faster, much easier and stronger.

We care about the quality and safety of our work. So for us this justifies the cost.” Of course, faster construction leads to shorter build time, which is another avenue to recoup costs.

Comprised of two basement levels with a ground floor and three levels of parking, the design for the US $82 million (AED300 million) project was influenced by the desire for optimum height without requiring a damping system, which could impact on the budget.

“The design is limited by sway, and how much you allow,” says Karas. “With this building, sway of 1.2m was acceptable, so we do not need a damping mechanism but it has been designed to accommodate this. Any higher and you would need one.”

He adds that concrete is very rigid and the heavy core provides ample stability, coupled with edge beams that transfer lateral loads to the core, lending greater stiffness to the building.

The number of labourers currently on site is 1,100, and Karas explains for a building of this height that reaches 290m, safety was paramount. To that end, a policy that sees no turnover of staff has been employed.

“We don’t change the labourers, we keep the same ones who are working on the same issues each time, so that they become familiar with it and they rise gradually. When you climb a floor a week or every five days it is better than coming straight onto the 40th floor,” he says.

With an estimated 12 months to go before completion, ASGC has little time to catch breath. Apart from the Emirates Crown, the contractor recently opened the Dubai Police Headquarters, while work is continuing on the billion-dirham Golden Mile development on the Palm Jumeirah. And with four towers in Business Bay plus a couple more on the Sheikh Zayed Road, ASGC will stay busy for some time to come.

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