Over the Top

Neither threat of earthquake, nor possible typhoon conditions, nor several disasters could bar this team from constructing the world's tallest building.
August 11, 2010

It stands just 660 feet from a major fault line, in a region that experiences dozens of temblors a year. It will face winds that exceed 100 mph and experience typhoon conditions several times a year. The soil it sits on is described by engineers as "less than desirable."

It's safe to say that Taipei is not the ideal location for any type of building, let alone the world's tallest.

But don't tell that to a determined Taiwanese government and an inspired Building Team that have endured incredibly stringent design guidelines, a controversial earthquake-caused crane accident that killed five construction workers, numerous schedule delays, and post-9/11 worries to construct a 101-story, 1,667-foot-tall giant in Taiwan's capital city.

Slated for completion this October, Taipei 101 officially became the world's tallest building last October when its 197-foot pinnacle was jacked into place, surpassing the 1,483-foot Petronas Towers in Kuala Lumpur, Malaysia.

The steel, concrete, and glass skyscraper sits in the city's Hsinyi district, dubbed the "Manhattan of Taipei," with high-end residential, retail shops, and office space geared mostly to financial firms. The $1.7 billion project includes 78 floors of office space stacked on a five-level retail mall and four levels of parking.

It is Taiwan's first a major building project to employ the build-operate-transfer model, where the government leases the land to a consortium of private investors for a certain time period — 70 years, in this case — after which the rights are turned back over to the government. Fourteen domestic companies, including the Taiwan Stock Exchange, back the Taipei Financial Center Corp. (TFCC), which is responsible for the planning, implementation, operation, and management of the tower.

 
At 1,667 feet, Taipei 101 towers over Taipei’s built environment. The $1.7 billion skyscraper consists of eight, eight-story segments stacked on a 25-story base. While the base slopes inward as it rises, the eight sections above slope outward seven degrees, creating a “stepping” effect. The inclining nature of the blue-green glass curtain wall helps cut reflective glare from the sun, allowing clear views of the city’s mountainous landscape. At the base of each eight-floor canted section, architect C.Y. Lee designed external fire safety decks, where people can transfer from one fire escape stair to another in case one stairwell is smoke-filled or damaged.


Mission made possible

For the government, Taipei 101 stands as a symbol of Taiwan's coming of age as a financial and political center in Asia. For the Building Team, the structure symbolizes much more.

"Sometimes you have to believe science fiction is real science," says Dennis C. K. Poon, P.E., managing principal with Thornton-Tomasetti Engineers, New York, the structural engineering consultant on the project. "Taipei 101 is proof that no matter what difficulties we face, we still overcome the challenge, with good teamwork."

Thornton-Tomasetti worked with local structural engineer of record Evergreen Consulting Engineering and design architect C.Y. Lee & Partners to develop a steel-concrete composite structure that would not only resist a 950-year earthquake and a 100-year wind storm, but also accommodate the "unique geometry" of C.Y. Lee's plan.

Lee's pagoda-like design breaks the building's massing into eight, eight-story segments stacked on a 25-story base. (The number eight represents "prosperity" in Chinese culture.) While the base slopes inward as it rises, the eight sections above slope outward seven degrees, creating a "stepping" effect that is meant to resemble bamboo segments springing from the ground — a Chinese expression for height.

Accommodating the outward sloping nature of the façade was one of the biggest challenges structurally, says Poon. Collaboration with Evergreen eventually led to a design that incorporates two main "super columns" 74 feet apart on each side of the tower that extend the full building height.

"Where the building slopes back every eight floors, there's a recessed area where we placed a pick-up truss to pick up all the sloping perimeter columns," he says. "The trusses tie the two super columns together, so all the loads get dumped back to the two super columns, and the load goes straight down."

Two outrigger trusses on each side of the building every eight to 10 floors tie the super columns to a braced core comprised of 16 steel box columns, providing overturning stiffness. A semi-rigid, sloping moment frame wraps the entire sloping perimeter of the building, giving ductility to the structure so it can deform to dissipate earthquake loading, says Poon. Reduced beam sections, or dog bone cuts, allow beams to rotate slightly to prevent buckling during an earthquake. The braced core beams are also designed to function as moment frame members.

At the lower levels, the eight super columns are about 8x10 feet and weigh 90 tons per section, the size of a small car garage, says Dugald MacKay, senior project executive with construction manager Turner International Industries, a division of Turner Corp., Dallas.

The hollow steel super columns and box-core columns were in-filled with 10,000 psi reinforced concrete up to level 62 to provide structural stiffness required to resist seismic loads. The concrete was pumped from bottom up to ensure uniformity of the material and to avoid interfering with the steel erection work above. Poon says using the high-strength concrete allowed the engineering team to design "relatively smaller" columns, compared with typical 6,000 psi concrete.

Below the 26 floor, two additional concrete-filled super columns and two corner columns on each face add stiffness to the structure and help combat wind and seismic-uplift effects.

The entire structure sits on a base supported by 550 piles, each approximately 260 feet long, drilled through 160 feet of soft soil 80 feet into the bedrock. Once drilled, each pile was tested for tension and compression. "They performed very well," says Poon. "I don't think the foundation is an issue now."

To lessen the effect of high winds, a tuned mass damper system was installed on levels 87-92. The TMD was added to the design scheme after early wind tests resulted in vibrations that were 30-40% more than recommended.

Designed by consulting engineer Motioneering Inc., Guelph, Ont., the system consists of a 730-ton steel ball suspended from eight steel cables on level 92 that will swing up to five feet in any direction to counteract the movement of the building. On average, the damper will move back and forth about one foot a few times each year.

Eight large viscous dampers cradle the sphere, dissipating the energy of the swinging motion of the ball, which consists of 41 layers of 12.5-cm-thick steel plates welded together. Eight "snubber" dampers are connected to a bumper ring that will prevent the damper from traveling farther than the five feet allowed.

The ball will be coated gold and showcased as an architectural feature of the building, according to C.P. Wang, senior partner with C.Y. Lee & Partners. He refers to the damper as "the heart of the building."

"We want people to see it and feel comfortable with it, so we placed restaurants and observation decks around that area," Wang has stated. It will be visible from several angles on floors 88 and 89.

Two smaller, flat-steel TMDs, each weighing about five tons, are located in the tower's pinnacle to protect it from fatigue.

To further lesson the impact of wind forces, Lee chopped off the four corners of the building, creating zigzagged or W-shaped corners.

Disasters strike

Adding to the project's complexity was a string of accidents and hiccups that delayed the schedule and cast a dark cloud over the project.

"We had so many problems, I think it's a miracle that we can get it done in this time and in this place," Lee said in a PBS television documentary.

The initial backlash centered on the tower's interference with aircraft landing at Taipei's Sungshan Airport. After a brief halt in construction to pan out a solution — including a proposed plan to downscale the skyscraper's height to 1,282 feet — Taiwan's Aviation Safety Council agreed to reroute landings and install a new landing guidance system at the airport to eliminate any threat to flight safety.

The project hit another snag on March 31, 2002, when a 6.8 magnitude earthquake shook loose two cranes from the 56th floor, killing five construction workers and injuring 10.

While the structure performed admirably during the temblor and aftershocks, the disaster left everyone emotionally scarred and put the project more than three months behind schedule — time the Building Team would never be able to recover. The halt in construction also reportedly cost the developer millions in wages, insurance premiums, and repair costs.

Construction resumed on June 28, 2002, following repairs to the podium roof, which was damaged by portions of the falling cranes, and an investigation by city officials into the cause of the crane failure. As a result, replacement cranes with pin-strengthened masts were installed.

Then on January 16, 2003, a fire broke out on the roof of the nearly completed five-floor shopping mall complex. No workers were injured, but the blaze, which reportedly was ignited by sparks from a welding torch, caused extensive damage to approximately 1,000 sf of the roof, and once again halted work on the project. The incident was the third fire to break out during the project.

 
The tower’s five-story podium took the brunt of the damage from two different accidents. In March 2002, portions of two cranes that shook loose from level 56 during an earthquake came crashing down onto the rooftop, killing five construction workers and causing extensive damage.


Ten months later — a week after the mall's grand opening — the mall had to be evacuated after several pedestrians were injured by steel bars and plates that fell from the 91st floor. The incident stalled work once again and heightened the continuing public outcry against the developer's safety measures, including the decision to open the mall before the completion of the tower.

As a result, the project is nearly two years behind its original completion date.

Office influx no problem

When Taipei 101 is completed this fall, it will unleash more than two million sf of office space into a market that is already considered to have an oversupply. But TFCC is relying on the tower's worldwide notoriety, high-tech infrastructure (fiber-optic and satellite Internet connections allowing speeds up to 1 gigabyte per second), relatively large floor plates (25,564 sf), and mixed-use amenities to charge a premium for office space. Its average monthly rent is about 30% higher than local average, but not the highest in Taipei, according to CB Richard Ellis realty.

Nearly one-third of the office space is reserved for TFCC shareholders, including Taipei Stock Exchange (which is expected to occupy up to six floors), China Development Financial Holding Corp., and Chinatrust Commercial Bank.

Pressure to fill the office space mounted after plans to include a 300-room, 18-floor luxury hotel fell through. TFCC was in talks with several hoteliers, including Four Seasons and Ritz-Carlton, but negotiations faltered in mid-2003 when the developer learned that pricey and time-consuming modifications to the interior structure would be needed to accommodate hotel occupancy.

TFCC's lead office agent, Jones Lang LaSalle, expects to see a growing interest as the tower nears completion later this year. The goal is to have 80% of office space leased by next spring.

Meanwhile, Taipei 101's 796,000-sf, five-floor mall, which opened last November to crowds estimated in the tens of thousands, has been a huge success, despite charging some of the highest retail rents in Taiwan. The 161-store, $350 million mall is 100% leased, attracting premium brands such as Louis Vuitton and Prada, and is expected to draw 15-18 million visitors in its first year.

All jacked up

For those involved in the project, the most memorable moment came last October when the 400-ton pinnacle was jacked into place. That's when Taipei 101 surpassed Petronas Towers in height. "Before that, we all knew that we were working on a very tall building, but in reaching 508 meters, I realized that I was part of a special team that had built the tallest building in the world," says MacKay.

         
 

RELATED ARTICLES FROM BD+C