[This article was originally published in The Ingenieur]
One of the tallest buildings in the world, and one of the most momentous feats of engineering, the Taipei 101 dominates the Taipei skyline. Located in the Xinyi as a symbol of Taiwan’s outstanding achievements in economic development.
The challenges of building the 101
Towering over everything else in the Taiwanese capital at 509m, the Taipei 101 displaced Malaysia’s very own Petronas Twin Towers from the top spot in 2004 until it was itself knocked off by the Burj Khalifa in 2010. The building of Taipei 101 was an immense challenge, as it is more difficult to design and build a supertall skyscraper in Taipei than in any other location in the world due to Taiwan’s vulnerability to natural events like typhoons and earthquakes. In addition, the weak soil conditions around the proposed building site needed to be overcome before building could commence.
Exceptional stability
The designers, C.Y. Lee & Partners, together with structural engineer firm Thornton Tomasetti ultimately solved this problem by having an extraordinarily solid foundation made of concrete that is 5m thick. This is reinforced with 380 piles driven 80m into the ground, extending as far as 30m into the bedrock. Each of these piles is 1.5 m in diameter and can bear a load of at least 1,000 tons. At the same time, Taipei 101’s structural framework is protected from the effects of earthquakes and fire by making use of both concrete and steel – essentially a hybrid structure. In comparison, other skyscrapers built in areas of low seismic activity, like the World Trade Center in New York, were built primarily from steel.
Starting their ascent from the foundation, 16 columns rise up to make the core of Taipei 101. These columns are boxes of steel plate augmented with filled concrete for added stiffness at lower levels. In addition, there are 8 so-called ‘super columns, up to 8’x10’ in size, distributed around the perimeter to help with the gravity load. All the steel used in the making of these columns is of 60,000 psi yield strength with a tensile strength no less than 570 N/mm². At the same time, the concrete used to reinforce the steel substructures is rated at 10,000 psi. All this underscores the formidable requirements and challenges of building such an exceptional structure as Taipei 101.
To counter lateral loads – in the form of wind and seismic forces – Taipei 101 uses what are called outrigger trusses internally. These trusses, which can be as tall as one or two storeys themselves, tie the core columns to the ‘super columns’ at every eighth floor.
The stability of Taipei 101 is further enhanced by the use of tuned mass dampers in the structure. Mass dampers are basically devices that help resist vibrations that can cause discomfort to a building’s occupants, cause structural damage and even ultimately result in catastrophic failure. In the case of Taipei 101, Thornton Tomasetti’s engineers designed and implemented a mass damper in the form of a 660 ton steel pendulum suspended from the 92nd to the 88th floors. This pendulum sways to offset oscillations in the building caused by wind gusts and earth tremors. There are two smaller mass dampers located in the spire to prevent undue vibration and damage in that part of the building owing to strong wind loads.
All of these innovations have led the engineers to predict that the structure can expect to survive once-in-2,500 year seismic events, that is to say, those which produce accelerations up to 0.5g at ground level.
The benefits of these devices, as well as the stable foundation in Taipei 101 have been proven on several occasions – in 2002 during the construction phase of the building, an earthquake of magnitude 6.8 struck Taipei. Even as the tremors toppled construction cranes from the building, the structure was found to have no lasting damage and work continued on shortly after that
Furthermore, in November of 2005, typhoon Longwang swept through Taiwan and caused damage to eastern counties of the country. Although the mass damper of the building swung noticeably, ultimately there was no damage reported or discomfort experienced by the building’s occupants.
The behemoth takes shape
The project broke ground in January 1998 and the first tower column was erected by primary contractors KTRT Joint Venture in June 2000. By July 2003 the roof of the tower complex was finished and the pinnacle of the structure was placed in October that same year. The adjoining Taipei 101 Mall, consisting of retail stores, clubs and restaurants was completed in mid-2001 and opened to the public in late 2003. The tower itself was formally opened to the public on Dec 31 2004, with then-President Chen Shui Bian and other dignitaries attending. A few hours later a fireworks extravaganza at the Taipei 101 celebrated the coming of the New Year.
Speeding through the sky
The building today houses numerous offices, a business and conference centre, observatories and restaurants well as retail outlets in the adjoining Taipei 101 Mall.
One interesting aspect of Taipei 101, generally unnoticed by the outside world, is their elevators. Even these are record breakers – in addition to the more ordinary elevators, there are two high speed elevators installed that travel at over 1000m a minute. These elevators, supplied by Japanese manufacturer Toshiba, are aerodynamically shaped, and feature their own active mass damper as well as an atmospheric pressure control system. To keep noise levels down, these people movers, the fastest elevators in the world, are also equipped with acoustic tiles, sound deadening insulation and isolated floor platforms. They are said to be able to travel from the 5th floor to the 89th in under 40 seconds, and all at a cabin noise level of 45 dBA.
The skyscraper that causes earthquakes?
Unfortunately, the construction of Taipei 101 itself seems to have caused some seismic trouble. Located at the Taipei basin which had historically experienced very little seismic activity, the building experienced micro earthquakes during construction. This eventually culminated in tremors directly underneath the tower that measured 3.8 (in October 2004) and 3.2 (in March 2005) on the Richter scale, serious enough to be felt by its occupants.
The theory advanced by geologist Cheng Horng Lin, a member of the prestigious Academica Sinica, is that the construction of the Taipei 101 may have reopened an ancient earthquake fault. In his paper published in the Geophysical Research Letters in 2005, he calculated that the stress to the surrounding ground due to vertical loading of Taipei 101 comes to a substantial 4.7 bars and this according to Mr Cheng, might very well have triggered the seismic activity under the building.
Although he stresses “no solid, substantive evidence has been found to substantiate that the changes in the seismic characteristics of the Taipei basin were a direct product of the construction of the massive high-rise building,” he calls for more research to be done in the matter.
The 101’s green credentials
On the 29th of July 2011, Taipei 101 received Leadership in Energy and Environmental Design (LEED) Platinum certification, in the category of Existing Buildings – Operations and Maintenance. This made it the tallest structure in the world to have received this award. In cooperation with their partners, SL+A, EcoTech and Siemens Taiwan, a total of 20 months and US$2 million was spent to implement policies and that would allow the building to meet the strict certification standards. With this certification, Taipei 101 can expect to gain energy savings of around US$1.2 million every year, but more than that, it leads the way for other existing buildings to follow suit.
The Taipei 101 stands tall as a testament to Taiwan’s economic achievement. An incredible feat of engineering from bottom to top, arguably it is also one of the greenest supertall buildings in existence. THE INGENIEUR salutes the builders, engineers and designers of this magnificent structure, with the hope that the field of supertall structures will continue to hold more in time to come.