Eight Liebherr tower cranes are working on the Dubai Marina Mall project, which upon completion in the second half of 2008 will include a 38-storey hotel and apartment tower and an eighty-storey shopping complex.

Located on the Dubai waterfront with the Dubai Marina complex, the project is being developed by Emaar Properties and built by ALEC, a wholly-owned subsidiary of the Al Jaber group.

Extending over a ground area of 42,000 sq m, Dubai Marina Mall is being marketed as an upscale lifestyle neighbourhood and a one-stop shopping and leisure attraction. It will sport a distinctive architectural style with a circular atrium that makes utmost use of the waterfront location. A pier, extending to the waterfront, will be lined with cafes and restaurants.

The 38-storey tower will feature the five-star 200-room Dubai Marina Mall Hotel along with 400 residential apartments, while the eight-storey tower will include 150 shops and restaurants. There will also be a two-level basement plus five-storey parking lot that will accommodate over 3,000 vehicles.

The project is being built to a tight 27-month schedule at a total budget of US$ 388 million.

The contractor initially worked to their own design involving eight trolley jib and a luffing jib crane. A major disadvantage of the initial design however was a large number of overlapping working radii.

Liebherr therefore proposed a configuration of eight cranes that avoided this problem.

The most pressing need was for cranes in the 280-mt class to meet the required load handling and tip load capacities, and all eight cranes are 280 EC-H models. Six of them deliver a maximum load capacity of 8 tonnes and consequently have the major advantage of high tip load capacity. The two other cranes are equipped for a load capacity of 16 tonnes maximum, the need for a high maximum load being the deciding factor.

Locations for these cranes were selected so that both material flow on the building site and also the working radii of the cranes ideally complemented each other.

In addition, attention was paid to the dismantling options for the individual cranes, which will be dismantled as the various stages for the work are completed.

Tower cranes when standing idle must rotate freely with their jibs according to the changing wind direction, and accordingly, the underhook heights of cranes with overlapping working radii must all be different.

At Dubai Marina Mall, three different hook heights are necessary. Since time considerations made it necessary to reduce crane-climbing procedures to a minimum, the tallest cranes were erected with a free-standing underhook height of 56.1 m and two tower base sections. Reinforced tower sections from the modular range make this possible.

The remaining cranes were arranged to rotate below the required heights for safety reasons.

When cranes are tied to a building they create stresses which act on the building and must be transmitted. This also acts on the tower structure of the crane itself and are rather different from those acting on free-standing cranes.

Forces known as tie-in forces are generated. A proportion of the crane’s torque is also transmitted via the tie-ins into the building. The extent of the tie-in forces varies a great deal with the height of the crane above the highest tie-in device and with the distances between the tie-in devices one above the other and/or above the foundation.

Depending on their size and the design of the crane, tie-in forces cannot be transmitted everywhere into the crane tower without restriction. Liebherr carries out structural studies for tied cranes.

The lowest possible number of tie-in devices represents not only a commercial advantage as regards materials sourcing and action on the building, but it also considerably reduces the cost of assembly and dismantlement and also crane idling time.

The load transmission from a crane into a building is effected across a bracing frame which surrounds the crane tower and in most cases across three tie bars which are anchored to the building with supporting brackets.

Cranes can be anchored to a building, for example, either on, in front of or beneath a building base plate.

The Dubai Marina development is a 4.6 million sq m mega project with 11 km of waterfront boardwalk and five marinas that can berth over 500 vessels.

A centrepiece of the development is the Dubai Marina Motor Yacht Club. Emaar is developing six residential projects within Dubai Marina. Three of them – Al Majar, Al Sahab and the Dubai Marina Towers – have been handed over to residents.

The master development has a projected population of 75,000, and there are already several thousand people living within Dubai Marina.


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