Stop the sway, a simpler way

Streamlining the counterweight systems that limit a building’s wobbles

Take note, high-rise builders and daring designers. You know those giant counterweights, called tuned mass dampers, that keep spindly skyscrapers and bridges from swaying in the wind? Well, now there’s a pint-sized portable tuned mass damper.

Wait a second. How does a regular tuned mass damper even work? A little background: especially at great heights, a structure can be strong without being stiff, and when it lacks stiffness relative to the forces acting on it—wind, footfalls—it can swing perceptibly. The building won’t topple, but the movement can cause occupants alarm, discomfort, even nausea. A notorious example, Boston’s John Hancock Tower, swayed as much as three feet off its base before dampers were added.

Increasingly common in Manhattan, the typical tuned mass damper (TMD) is essentially an enormous counterweight on springs or a pendulum, built into the top portion of a tower. When high winds push on the building, the weight swings in the opposite direction, staying the tower’s shift. But in order to make it work, engineers have to “tune” the damper to match the building’s natural frequency, ensuring that the weight swings just enough to counteract the wind. (Frequency being the speed of a vibration.) Practical Engineering explains it all with a fun video here.

The drawbacks are size and cost. For example, the 728-ton steel ball that stabilizes the 1,667-foot-tall Tapei 101 tower in Taiwan cost $4 million—and it takes up six stories of prime real estate.

A lighter package

By contrast, a portable tuned mass damper, under development at Virginia Tech, weighs about 275 pounds. And a building owner with no technical training can adjust the damper’s settings with a five-dollar iPhone app.

Of course, the damper itself will cost more than $5, but it will be affordable, says its inventor, Mehdi Setareh, an architecture professor and the head of the Vibration Testing Lab at Virginia Tech. “What I’m trying to do is reduce the cost so it can become more common,” Setareh told us. “It’s like what Henry Ford did with cars.”article-image.img.490.high

Setareh’s invention is best suited to those modern buildings constructed of lightweight materials and given swooping, eye-catching shapes with computer-aided design. Setareh is himself an award-winning structural engineer who helped design the dramatically cantilevered headquarters of MFP Automation Engineering (right).

1376915

Such bold designs have become more common—and along with them, so have complaints about noticeable vibrations, according to Setareh. His lab has studied and helped modify structures such as a theater balcony in Detroit and the monumental stair in the Zaha Hadid–designed Broad Art Museum in East Lansing, Michigan (left). “The floors are designed for strength,” Setareh hastened to point out. “When people walk on the floor, it holds the load, no problem.” But a slight bounce gives users the unwelcome impression of shakiness. “It can be scary, or at best annoying.”

5291203

A prototype portable tuned mass damper. (Photo Courtesy of Virginia Tech)

Rather than sacrifice aesthetics or boost costs by building with heavier beams, said Setareh, architects (or, after the fact, building managers) can apply a simple fix. Acting like a shock absorber, the portable tuned mass damper (PTMD) consists of a weight on springs, tuned to have a natural frequency close to that of the floor. When the floor is rattled by foot traffic, the springs are activated and the movement of the weight pushes back against the movement of the floor, neutralizing it. “When the floor goes down, the damper mass goes up,” Setareh said, “and when the floor goes up, the mass goes down.”

The device sits two feet high and weighs a fraction of the floor, but it compensates by moving ten to twenty times faster than the floor vibrates. “So even though the mass of the [PTMD] is, say, 200 pounds, it’s like 4,000 pounds of force moving against the floor,” Setareh said. “That’s how it reduces the vibration substantially,” up to 60 percent in the Virginia Tech lab’s testing facility (see below).

A result of rocketry

That’s a fine solution for a variety of unique buildings—hospitals, theaters, corporate headquarters. But what about a straightforward residential high-rise? It’s hard to imagine a small, convenient version of the titanic TMD at Tapei 101.

And yet, a team at NASA has developed a damper the size of a coffee can (though it sits in a long pipe filled with water) that can stop a tall building’s shakes in a heartbeat. Spun off from rocket technology, a variation of this “disruptive tuned mass” has been installed on the new 32-story 461 Dean in Brooklyn, the world’s tallest modular building. It turns liquid into a secondary mass that absorbs and dissipates the energy of a building’s vibrations.

PS_8

461 Dean, the world’s tallest modular building.

Engineering firm Thornton Tomasetti licensed the technology and adapted it to 461 Dean (right), which is built of lightweight steel modules. Thornton Tomasetti’s rooftop system, which they call a fluid harmonic absorber, consists of four U-shaped PVC pipes, each 50 feet long and three feet in diameter. Air springs are fitted to the outside of the pipes and tuned to a certain “sloshing frequency,” explained Michael Wesolowsky, a Thornton Tomasetti engineer. The tubes are pressurized so that during a wind or seismic event, air pushes on the water, and then vice versa.

“The liquid is tuned to slosh back and forth at exactly the same frequency as the building’s movement, but out of phase,” said Wesolowky, “pulling the building back in the opposite direction,” thereby keeping it steady.

PS_9

Installation of fluid harmonic absorbers on 461 Dean’s rooftop. (Photo courtesy of NASA)

“It’s like the air spring in your car,” added Elisabeth Malsch, another Thornton Tomasetti engineer, “if you have a newer, fancier car.”

Already, the system has performed well on high-wind days, Malsch said. And it has advantages over the gargantuan conventional TMDs. The absorber at 461 Dean (the first of its kind in a commercial application) is “cheaper, lighter,” said Malsch. “It required very little reinforcement” to the building below. It’s also easier to tune, not to mention maintain. After all, “we know how to patch leaks in pipes,” Malsch said.

Like the PTMD out of Virginia Tech, the fluid harmonic absorber can be installed after initial construction is complete, if a structure turns out to behave differently than predicted in high winds. The Smithsonian speculated that historic landmarks built before earthquake codes might be retrofitted with the NASA-bred system, another benefit of which is its fast-acting nature. (Skyscrapers can still sustain damage during the few seconds it takes for a quake to activate a conventional, pendulum-style damper.)

Malsch can attest that older buildings are good candidates for the addition of such a cutting-edge streamlined damping system. Her office is in Manhattan’s 40 Wall Street, at 71 stories the world’s tallest tower when it was completed in 1930 (before being surpassed by the Chrysler Building a few months later). On windy days, the structure’s age is apparent—or audible.

“Every six seconds,” said Malsch, “you can hear it creak.”

This post was written by Suffolk Construction’s Content Writer Patrick L. Kennedy. If you have questions, Patrick can be reached at PKennedy@suffolk.com. You can connect with him on LinkedIn here or follow him on Twitter at @PK_Build_Smart.

The wows, what-ifs, and “What is that?” of high-rise design

There’s still time to enter your jaw-dropping design in eVolo Magazine’s 2017 Skyscraper Competition. But you’d better draw fast if you want to make the early-bird deadline: it’s today, November 15. (The final deadline is January 24, 2017.)

The contest awards architects with the biggest and boldest imaginations, recognizing “outstanding ideas that redefine skyscraper design [using] novel technologies, materials, programs, aesthetics, and spatial organizations,” according to the entry guidelines. Check out some of last year’s winners below. Even if none of these structures ever end up being built, the renderings provoke thought about what a skyscraper could be, and perhaps some elements of these far-out designs will be incorporated into the tall towers of tomorrow.

drone-skyscraper

Photo courtesy of v2com

The Hive: Drone Skyscraper, by Hadeel Ayed Mohammad, Yifeng Zhao and Chengda Zhu. (Second place in 2016) The architects envision this vertical drone hangar as “an infrastructure project that can better meet the emerging demand for incorporating advanced drone technology into daily life in New York City.”

 

sustainable-skyscraper-enclosure

Photo courtesy of v2com

Sustainable Skyscraper Enclosure, by Soomin Kim and Seo-Hyun Oh. (Honorable mention in 2016) The design repurposes an existing skyscraper, encasing it in a climate adjusted zone and installing an “energy purifying system” that captures solar energy and harvests rainwater.

 

air-stalagmite

Photo courtesy of v2com

Air-Stalagmite, by Changsoo Park and Sizhe Chen. (Honorable mention in 2016) In this towering air purifier, “a gigantic vacuum placed at the bottom of the building sucks polluted air to be cleaned by a series of air filters located on the higher levels. The particles are then accumulated and used as building material to further construct the skyscraper.”

 

valley-of-the-giants

Photo courtesy of v2com

The Valley of Giants, by Eric Randall Morris and Galo Canizares. (Honorable mention in 2016) In a barren area of Algeria, the architects propose “a series of towers that would (1) house plant-spores, (2) produce, collect, and treat water, and (3) pollinate the surrounding landscape, catalyzing the production of an oasis in the region.”

 

vertical-shanghai

Photo courtesy of v2com

Vertical Shanghai, by Yuta Sano and Eric Nakajima. (Honorable mention in 2016) It may look like a pile of houses that tumbled out of a toy chest, but the architects designed this structure as a homey, diverse antidote to the waves of plain high-rises wrought by China’s rapid urbanization. This one deserves a second look—see the sectional rendering below. Any contractor care to bid on the project?

vertical-shanghai-2

This post was written by Suffolk Construction’s Content Writer Patrick L. Kennedy. If you have questions, Patrick can be reached at PKennedy@suffolk.com. You can also connect with him on LinkedIn here or follow him on Twitter at @PK_Build_Smart.

It’s a building, it’s a city, it’s a “super building”

Imagine leaving your apartment one Friday morning to get in some shopping at the mall before your doctor’s appointment at the local hospital. Then, you decide to take a long stroll on your favorite nature trail through the park with plenty of time to pick up the kids from school. Later, with the kids and their friends in tow, you take public transit to the movie theater to celebrate the start of the weekend. After your busy afternoon, you drop off the kids’ friends at their apartments and you head home to tuck your children into bed.

Now, imagine you did all that without ever stepping foot outside your building. The year is 2050 and you live in a “super building.”

Like today’s major cities, super buildings will consist of millions of inhabitants and their own infrastructure with shopping, recreation, medical facilities, theaters, schools and even parks. The major difference is that the entire “vertical city” will be concentrated under one roof within a single massive structure. Super buildings could stretch miles into the sky and consume entire city blocks. They could recycle their own water and generate more energy than they consume. Sound like something straight out of the Jetsons or Interstellar? Maybe. But the truth is that super buildings could be closer to becoming a reality than you think because there are developers and architects among us who believe these enormous structures may be our best option for dealing with the rapid demographic and environmental changes that are affecting our planet.

Continue Reading ›