by The deadly 7.4-magnitude earthquake that struck Taiwan on Wednesday and left at least 9 people dead also damaged more than 100 buildings across the island, according to the National Fire Agency (NFA). About half of them were near the epicenter in Hualien County, where four structures partially collapsed.
In the capital Taipei, just 80 miles away, buildings shook violently during Taiwan’s strongest earthquake in 25 years. But in a triumph of modern engineering, the Taipei 101, the world’s tallest skyscraper, emerged from the island’s most recent seismic event unscathed.
Footage from the quake appears to show the 1,667-foot-tall tower swaying slightly, with its structural flexibility helping to cope with the quake’s powerful motion. This movement perfectly demonstrated how the skyscraper’s single most important defense against earthquakes is the material it is made of: reinforced concrete.
By combining the compressive strength of concrete with the tensile strength of steel, the material makes the building flexible enough to be steered, yet rigid enough to withstand the high winds and typhoons that frequently hit Taiwan. (The principle that buildings can withstand seismic forces by moving with they have underpinned, rather than opposed, traditional architecture in earthquake-stricken East Asian countries for centuries, from Japanese pagodas to Chinese palaces.)
High inside the tower, however, another technological innovation helps protect the 101-story skyscraper—a giant orb-like device called a tuned mass damper.
A huge counterweight
Suspended from 92 thick cables between the 87th and 92nd floors, the golden steel sphere can move about 5 feet in any direction. As a result, it acts like a pendulum that counteracts (or “suppresses”) swinging motion.
“It’s basically a very large counterweight,” explained Stefan Al, author of “Supertall: How the World’s Tallest Buildings Are Reshaping Our Cities and Our Lives,” in a phone interview. “In the case of Taipei 101, it is 660 tons. That sounds heavy, but if you compare it to the total weight of the building, it’s only a fraction.
“When a building starts shaking, (the tuned mass damper) will move in the opposite direction. In the case of Taipei 101, it’s suspended … so it’s going to end up as the tower goes and absorb the kinetic energy by moving in the opposite direction,” Al said, explaining that hydraulic cylinders do between the ball and the building this energy is converted into heat, which is then dissipated.
Tuned mass dampers are used in skyscrapers around the world, including the “super-skinny” Steinway Tower in New York and Dubai-shaped sail Burj al-Arab, which has 11 of them. The device crucially protects against the violent motion caused by “harmonic vibrations,” which could cause structural failure during an earthquake, said Al.
“(That’s) when buildings start vibrating at their own resonance,” he said, likening the phenomenon to a tuning fork. “This can lead to a collapse, (as) the building will start shaking faster and faster and faster.”
Tuned mass dampers, also known as harmonic absorbers, are “tuned” to resonate at the same frequency as the building – but with earlier or later starting wavelengths, helping the potential energy spread disastrously.
The stability they provide can also reduce the uncomfortable – or even offensive – effect that swaying building occupants can have in high winds.
Structural support
Taipei 101, designed by the Taiwanese firm CY Lee & Partners, was the tallest building in the world from 2004 until 2007, when it was surpassed by the Burj Khalifa in Dubai. An observation deck that looks at its newly tuned moisture mass is now an attraction for visitors, especially when it moves during strong winds.
However, the giant sphere is not the only design feature that helps stabilize the tower, which is close to a major fault line.
For one, the skyscraper rests on very deep foundations – that is 380 piles of reinforced concrete and steel drilled into the bedrock below. Above, the core of the building is connected to a series of “mega-columns,” located around its perimeter, by massive steel outrigger trusses.
The high-rise meets strict anti-seismic building codes as would be expected on an island located on the “Pacific Ring of Fire,” which runs around the edge of the Pacific Ocean and is the cause of massive activity seismic and volcanic from. Indonesia to Chile.
But while the design has also undergone extensive digital modeling and “shake table” testing (in which scale models are tested on a device that simulates the movement of an earthquake), how a building like Taipei 101 would perform in a seismic event remains to be seen. stronger or closer. , to an extent, theoretically.
“Even though we have computer simulations, there’s something about the physical that we can’t really get from digital simulations,” Al said, adding: “Despite our technological advances, we’re still testing (designs) in wind tunnels and in shaker tables. “
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