Leslie Robertson, head of structural engineering consultancy, LERA, explains why rotation is good, Dubai's energy use is not so good, and why design criteria hasn't changed since 9/11.
Your latest project is David Fisher's rotating tower in Dubai. What is special about this one compared to other developments of its kind?
Each floor of the building will be rotating by itself, rather than the whole building as one unit. And each floor will rotate at different speeds, which means the shape of the building will change continuously. The speed of rotation can be substantially quicker because when you rotate the whole building you are rotating the lift shafts and mechanical shafts at the same time, so you might rotate it once a day, once a week or even once a month. But here you'll be allowed the entire perspective in a much shorter timeframe. There are times when you may want it to have a certain shape - during a big windstorm, for example, we can orient the building so that it is best suited to accommodate high wind speeds.
An important feature of the tower is the wind turbines between each floor. Are you trying to raise the bar in terms of ÃƒÂ¢Ã¢â€šÂ¬Ã‹Å“green building' in this region?
Dubai has a very serious problem because it is not generating alternative energy, and not only that, it is also automobile-dependent. Dubai is a huge energy consumer on a per capita basis. That is wrong, it has to change and everybody knows it. There may be a lot of interest in using alternative energy sources in Dubai but there is not a lot going on. On this project we are talking about producing a very substantial amount of electrical generation, whereas other projects I've seen that incorporate horizontal-access turbines and propeller blades, the total amount of energy produced is relatively minor. But this building will be able to produce enough energy to power many other buildings, not just itself. This will be an energy generator, not an energy user.
You were the structural engineer for the World Trade Centre in New York. Has your approach to tall building design changed following the events of 9/11?
After 9/11 we got a lot of enquiries about buildings we had done in the past and buildings we were working with at the time, and the basic issue was: ÃƒÂ¢Ã¢â€šÂ¬Ã‹Å“would you change your design for the building you are doing?' I said: ÃƒÂ¢Ã¢â€šÂ¬Ã‹Å“no I wouldn't.' We still design for unforeseen events, so there's really been no change in our approach because of the attacks. However, following that event I assumed we would have most of our commissions cancelled, but instead of that we were asked to visit a lot of our buildings and talk generally about the projects and the design, and why we felt that they shouldn't do anything but continue building.
So there was nothing about the design of the World Trade Centre that you would have changed?
The World Trade Centre was designed for impact of aircraft and the building withstood the impact of aircraft without falling. The towers would be standing there today were it not for the subsequent event of the fire. In any event a structural engineer has the responsibility to produce buildings that are safe. All of our buildings are designed to be very robust and strong. They are able to accept unforeseen circumstances and they are very ductile so you can bend them without breaking them.
But if skyscrapers are potential targets, should extra security measures be introduced?
There's certainly a place for security. A lot of things can be done to enhance security and I'm for that. I'm just not in favour of constructing buildings that are not great places to live and work. One major design specification I always attempt to enforce is to keep parking areas away from underneath tall buildings. We are not always successful in doing this as a lot of developers allow parking inside. If there was ever an easy way to bring a car bomb into a building, it is through underground parking. Don't have parking inside the building. Keep it outside with a reasonable stand-off between the building and the parking.
Are you involved in the redevelopment of World Trade Centre site?
Other people in our company are involved in rebuilding that site but not me. I put 10 years of my life into that site and I think that's enough.