Spin City

Last month, architect David Fisher revealed his latest plans for a 420m rotating tower to be built in Dubai. Bernadette Redfern speaks to him and analyses the design.

When David Fisher announced this summer that his first rotating tower would begin construction in Dubai, by the end of the year, closely followed by his second tower in Moscow, his idea was met with bemusement by the engineering community. The concept of a self-powered rotating structure, which is 85% prefabricated with just a 22-month construction period, seemed too good to be true. "Most buildings of this size would take 40 months," he says.

The truth is that there are still a lot of details to be confirmed and a detailed design is being carried out by Leslie E Robertson Associates (LERA), most famous for designing New York's Twin Towers, has a reputation for turning complex ideas into workable structures. But, so far, details of how the rotating towers will work structurally have not been forthcoming.

The tower itself consists of a tubular concrete core. "The strength will come from the thickness of the core," says Fisher. "We will pay special attention to the concrete and steel, and the wall thickness will vary." He confirms that it will be cast in situ, but cannot provide exact dimensions, thicknesses or concrete strength, and will only reveal that it will not taper from the outside, but will remain a uniform tube. "It will be designed to take the maximum dynamic loading," he says.

To calculate this loading, a huge amount of modelling will have to be undertaken as the floors, which are a smooth triangle in plan, can move at varying speeds and therefore create a vast combination of different shapes.

"The tower is a constantly changing shape, so they'llneed to run a massive series
of wind studies," explains associate director, Andrew Weir of structural consultancy, Expedition Engineering. "It's also very slender. Having the whole weight running down the centre helps, but there will be significant acceleration at the top."

2000
Number of prefabricated pods hooking onto the core

20
Maximum number of rotations per day

£15M
Cost of buying a floor in the tower

Click here for typical floor plan

The floors will comprise more than 2,000 prefabricated steel and aluminium pods, which will be manufactured in Italy, where Fisher's practice Dynamic Architecture is also based. These pods will be lifted into place with between 30 and 42 per floor and will appear to cantilever out from the core. "The units will hook onto the core and connect to create a single unit. These are mechanical connections – this building is a machine for living in," says Fisher.Each of the units is set to rotate around the core, with a 360-degree rotation taking approximately 1.5 hours, and owners of whole floors can set the speed. "Research shows there are no negative effects on residents," says Fisher.

Although the building documentation states that the structure will be "the first building designed to be self-powered [and] it achieves this feat with wind turbines fitted beneath each floor", engineers with experience of such structures are sceptical.

"There is not a hope in hell that the energy generated from wind loading would create enough power to move the floors," reveals a senior structural engineer. "A stationary unit has an enormous amount of inertia to overcome."

Fisher admits that the building will need to be connected to the grid to meet all of its power needs, and says more research must be carried out on the expected performance of the turbines and solar panels planned for the tower. But he says he does expect that at peak wind loading the tower will sell electricity back into the grid. "We are working on the design and we have an Italian universities group, ABITA, involved," says Fisher.

Perhaps the biggest question that remains to be answered is how services, such as water, waste water and electricity, will reach the rotating floors. Fisher says that he has solved the problem with a single "smart connection" that enables constant service provision whenever the building is in motion – but he refuses to reveal the details.

Despite the lack of available information regarding the design aspects, so far, there have been 790 requests for more information from interested buyers. This is an encouraging start for the developer Mejren Enterprises, headed by Sheikh Mejren bin Sultan.

The future of the scheme rests on getting approval from the Dubai Municipality and once this happens, the site will be revealed. Dubai recently set out its determination to encourage green design by introducing a sustainable buildings code in January earlier this year.

"A rotating structure is clearly not an efficient structure," says Weir. But Dubai is also famous for pushing the boundaries of possibility, which this structure certainly does. This puts Dubai in a catch-22 situation and leaves its government with an interesting decision to make.