Saturday, Sep 20, 2008
Gulf News
Dubai: Although it is no longer the world's tallest building after being overtaken by the Burj Dubai in July last year, the Taipei 101 tower in Taiwan's capital has kept its appeal with visitors.
It is still the highest man-made structure in South Asia, and, as such, attracts visitors not only with its bamboo-like structure, but also its most imposing feature: The building accommodates the world's heaviest so-called mass damper in the shape of a giant golden sphere that hangs on enormous steel cables directly below the roof of the building at a height of approximately 500 metres above street level.
Wonder of engineering
On a recent visit to Taipei, guide Linda Chen proudly announces that the whole building had been praised as one of the Seven Wonders of Engineering by the popular US television series Discovery Channel, mainly due to its sophisticated earthquake resistant structure, the world's fastest elevator and, at least, the huge damper ball hanging on the top that weights some 650 tonnes.
Situated in Taipei's buzzing financial district, the 101 tower surmounts all surrounding buildings by far. It is a manifestation of a singular architectonic vision of Taiwan's leaders, almost a foreign body in a city with a peculiar mixture of traditional Chinese houses, low-rise buildings and broad avenues situated in a relatively narrow, bowl-shaped valley.
The first exciting experience after entering the 101 tower and passing the imposing lobby area is to travel upwards with one of the 61 elevators, of which two are moving directly from the ground to the observatory platform at a speed of 1010 metres per minute, which means that the platform can be reached in less than 40 seconds.
The high speed elevators are technical miracles on their own, Chen explains. Constructed by Japanese tech giant Toshiba, the elevators are designed to relieve pressure gradients that occur while travelling at such a high vertical speed. Additionally, the outside shell of the elevator has to withstand temperatures of up to 1000 degrees Celsius that may emerge from traction.
But, after reaching the top platform of the 101 tower and enjoying the spectacular view of the city from a half kilometre height, the real surprise is the enormous damper ball hanging between floor 88 and 92. It has been attached there to give the building an overall stability to withstand earthquakes, typhoons and strong winds. The damper reacts like a pendulum to the building's movements and reduces the amount of possible vibrations up to 40 per cent.
During construction, the ball was too heavy to be lifted by crane as a whole. Canadian engineering company Motioneering divided it into 41 layers and assembled it on the 88th floor, where it now is entangled by steel cables that allow it to swing 1.5 metres in each direction. Bumpers prevent the ball from exceeding this limit. The pendulum in the sky came at a cost of $4million (Dh14.7 million), Chen says.
Given the mass damper together with the building's foundation, the 101 tower is said to be one of the most stable buildings ever constructed.
The foundation has been built by using 9,000 tons of steel and 26,000 cubic metres of concrete and is reinforced by 380 piles that reach up to 80 metres into the ground. On March 31, 2002, the building - then 56 floors high - withstood a 6.8 magnitude earthquake with no structural damage.
Designed by Thornton-Tomasetti Engineers, a New York engineering firm that also provided the structural design of the Petronas Towers in Kuala Lumpur, the Taipei 101 withstands gale winds of up to 200 km/h and strong earthquakes. The shape reminds of a series of pagodas or a stick of bamboo, a reason why residents labelled it "Bamboo Tower" - having Taiwan's native plant in mind.
Earthquake engineering expert Dr Shapour Mehrkar-Asl, who works for WSP Group - an engineering consultant - in Dubai, speaks to Gulf News on the earthquake resistant buildings here.
Gulf News: Is there a serious threat of earthquakes in Dubai?
Dubai is in a low seismic zone. This would mean that the potential of earthquakes that cause significant damages and ground movements is low. However, as we are close to the southern part of Iran which has a relatively high seismic zone, the results of earthquakes in Iran would cause ground vibrations which cause our buildings to shake.
What is to be done to make a high-rise structure earthquake resistant?
The effect of earthquake on a building is like when you are in a car and suddenly the car stops. If you don't use the car's seat belts you would move forward a lot and may even hit the windscreen. In Dubai the lift shafts and stair wells are normally designed to act like the seat belts in a car to control the movements.
What building codes are used, are they good enough?
At the moment we are required to use an American code which has international maps that define the level of force buildings have to be designed for. This is a widely used code in the world. It has divided different parts of the world into Zones. The strongest earthquakes come in Zone 4; the lightest in Zone 1.
There are two Zone 2s; one is Zone 2A and the other is Zone 2B. UAE has been considered to be Zone 2A which is slightly less that zone 2B. In terms of percentage of forces, Zone 2A is 37.5 per cent of Zone 4 forces. There have been studies done which show that the actual levels of earthquakes in Dubai are slightly below Zone 2A; therefore by using Zone 2A forces we have a reserve of strength on our hands.
What is the maximum height a building can reach to be still earthquake resistant?
To be honest, in the UAE it is not the earthquake which limits the height. The height is restricted by be a number of factors; the most important is the strength of the material we are using. Today, in the UAE we have the tallest building in the world. This has been as a result of using the strongest concretes in the world.
When I started to be a structural engineer, which was over 30 years ago, concrete strengths were about 30 per cent of the concretes that we use now in the UAE. This means that we can build taller and safer buildings. So the limit of height does not come as a result of the earthquake but as a result of the strength of materials we are using for the construction of our buildings.
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