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).

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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.”

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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.

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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.

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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.

A park or farm in the last place you’d look

Inventive designs cram bounties of vegetation into unexpected spaces

In dense and growing cities, plant life is at a premium. Urban planners know the benefits of a bit of botany. As San Francisco-based advocacy group Canopy explains, trees suck up carbon dioxide while they pump out oxygen, making our air cleaner. Trees’ leafy cover provide shade, while their roots mitigate flooding. Grassy parks visually break up our concrete streetscape with green space, and they promote community interaction and physical activity. All of this makes city living healthier than it would be otherwise.

But designers have to be pretty creative to pursue these goals in the midst of a development boom. That’s why around the world, architects are finding innovative ways to carve out some elbow room for greenery in the built environment.

green2Pictured above and at right, the Botanic Center in Brussels represents one such solution. The architect, Vincent Callebaut, has proposed dramatically sprucing up a 1977 concrete apartment block with the addition of 274 planter beds to the façade and a striking “Chrysalis” on the roof—a steel-and-glass observation pod filled with a variety of plants and topped with wind turbines and a solar panel array.

From Tapei to New York City, from structures that reach the sky to tunnels that run beneath our feet, here are a few other designs that feature flora in unlikely quarters.


Agora Garden

Another Callebaut creation, this twisting tower in Tapei topped out last November and is slated for completion next September. (Inhabitat has a very cool slideshow of Agora Garden under construction.) As you can see from the above rendering, every one of its 22 stories will be packed with tree- and shrub-laden balconies. And these aren’t simply aesthetic amenities. Callebaut intends for residents to have sufficient outdoor space to grow their own produce. He estimates the plants will absorb 130 tons of carbon dioxide a year. On top of that, the building will incorporate solar energy, rainwater recycling, composting and other measures to further limit its impact on the environment.

Low Line

The Lowline

You may have heard of New York’s High Line, a park running along a disused section of elevated rail tracks. The Lowline takes that idea underground. An abandoned trolley subway tunnel beneath the streets of the Lower East Side will serve as the site for the world’s first underground park. How will the park’s plants flourish? Solar irrigation. A network of mirrors brings sunlight through pipes down into the tunnel, where the sun, normally, wouldn’t shine. The development team built a proof-of-concept Lowline Lab that proved a popular attraction over the past year or so. That bodes well for the full Lowline, projected for completion in 2021.

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Pier 55

British starchitect Thomas Heatherwick designed this 2.4-acre park to be sited atop an artificial island in New York’s Hudson River. Alternately called Diller Island after its developer, Barry Diller, Pier 55 is slated for completion in 2019. A distinctive element of the island is its support system. Heatherwick designed it to lie upon hundreds of concrete columns rising out of the water to varying heights, for a rolling landscape effect, up to 62 feet. While traditional steel piles have already been driven into the bedrock in the center of the site, the mushroom-shaped columns about the perimeter will be hollow precast concrete piers, to be filled with concrete on site.

Although the Army Corps of Engineers signed off on the design, the project recently stalled in federal court. However, it has weathered several court challenges so far, and it has the support of the mayor, the governor, and neighborhood groups. In any case, the design suggests the possibilities opened up by building on water—a long tradition in coastal cities. (Stay tuned to this blog for more on artificial island construction.)

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Mashambas

Skyscrapers are typically found in cities. But the winners of the eVolo Magazine 2017 Skyscraper Competition, Polish architects Pawel Lipiński and Mateusz Frankowski, instead direct our attention to rural, sub-Saharan Africa, where more than 40 percent of people live in absolute poverty. (The United Nations defines absolute poverty as a condition in which people suffer from not only low income but also a lack of access to food, safe drinking water, shelter, and other resources.) To attack this problem, Lipiński and Frankowski imagine a farming and educational center in a temporary, modular high-rise that can be assembled, disassembled, and transported from one site in need to another.

The Polish team’s prize-winning concept, Mashambas (from a Swahili word meaning farmland) would feature a permanent farmer’s market on the ground floor, with elevated “fields” for farming on the floors above. The structure would also contain warehouses—for fertilizer, seeds, drones, and equipment—and classrooms. In the architects’ vision, staff would use those classrooms, as well as the farming modules, to train local subsistence farmers in modern agricultural practices. The farmers would then move on to growing crops in their own fields nearby. Eventually, the community would become self-sufficient, and the Mashambas tower could be dismantled and shipped to the next village, leaving behind the anchoring farmer’s market and one-story warehouses.

To be sure, a vertical farm might work at least as well in a cramped urban environment, but by siting their winning eVolo design in a developing rural region, Lipiński and Frankowski are raising awareness of the struggle farmers there face.

Mashambas interior

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 Space Needle, the Jetsons, and what today’s futurists see for tomorrow

It looks like a flying saucer, perched atop spindly, upward-swooping legs. It’s as if a UFO and its exhaust trail were frozen mid-takeoff. Like something out of a sci-fi movie. And that’s the point.

In case you missed it, the Seattle Space Needle recently turned 55—old enough to get the senior discount at Old Country Buffet. Much like the Eiffel Tower in Paris, the Space Needle was built for a World’s Fair; attracted its share of criticism; and is now a landmark that defines its city’s skyline. And while this Space Age artifact may seem a tad dated now, its influence has rippled across the decades and perhaps—if a company called Arconic fulfills its vision—will continue to alter skylines in 2062.

Speedy in Seattle

The Space Needle was conceived as the centerpiece of Seattle’s Century 21 World’s Fair, a showcase of tomorrow’s technology. It was vintage midcentury: can-do optimism, tinged with Cold War urgency. The Soviet Union had shocked Americans when it sent the first satellite into orbit in 1957, kicking off the international space race. But in the JFK era, with federal dollars flowing to scientific research, and finned automobiles speeding down superhighways, anything seemed possible.

Rising 605 feet high—then the tallest structure west of the Mississippi—the Needle was built in just 400 days, at a cost of $4.5 million. The foundation, which was 30 feet deep and 120 feet across, took 467 cement trucks about twelve hours to fill. It was the longest continuous concrete pour attempted in the West at that time.

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Work on the Space Needle’s immense foundation. (Photo courtesy of the Museum of History & Industry)

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The Needle’s top house under construction. (Photo courtesy of the Seattle Post-Intelligencer)

Including 250 tons of rebar, the foundation weighs 5,850 tons; the Needle structure itself weighs 3,700 tons. This means its center of gravity is just five feet above the earth’s surface. The Needle is fastened to the foundation with 72 thirty-foot bolts.

Not only can the Needle survive earthquakes (e.g., one in 2001 that measured 6.8 on the Richter scale), but it was designed to withstand winds of up to 200 miles per hour—double the code requirements in 1962.

But what struck most was the daring design of the tower and its bulbous top house. The spacecraft look was deliberate. Initially, the building was painted with colors “Astronaut White,” “Orbital Olive,” “Re-entry Red,” and “Galaxy Gold.” As the building seemed to reach for the stars, it signaled a nation’s upward progress.

Construction was completed in December 1961. The Needle’s signature rotating restaurant held an opening gala on March 24, 1962. The Century 21 World’s Fair officially opened on April 21.

Seattle_Space_Needle_CropUnlike other architectural relics of the period—e.g., unloved Brutalist exemplars such as Boston’s City Hall and the Salk Institute in La Jolla, California—the Space Needle appears on T-shirts and postcards, earned official Seattle landmark status at age 37 (in 1999), and remains one of the city’s most popular tourist destinations. While many Sixties buildings raised eyebrows, the Needle prompts smiles as well. It may be that, along with its aspirational spirit, the tower’s very cartoonishness is what makes it so endearing—and enduring.

The Jetsons connection

That drawn quality quickly translated into actual cartoon form when The Jetsons debuted on TV in September 1962. The series imagined a family in 2062. The Jetsons and their contemporaries drove flying cars, employed robot maids—and lived in high-rises that looked a lot like the Space Needle. In case you were deprived of re-runs as a child, here’s the program’s opening:

The resemblance of the Jetsons’ home to the Space Needle was no accident, animator Iwao Takamoto told the New York Times in 2005. The “skypad” on stilts took direct inspiration from the Seattle tower.

Art imitates life, and vice versa. A new engineering company called Arconic—spun off the aluminum giant Alcoa—has taken inspiration from The Jetsons to reimagine the world of 2062. Arconic’s updated Jetsons drive flying cars and live in skypads that make use of technologies currently in development or, in some cases, available already. The company hired filmmaker Justin Lin (Star Trek Beyond) to illustrate their vision with this video:

Arconic’s futurists predict that three-mile-high skyscrapers will be built using 3D printing. The technology will allow for more organic, nature-inspired shapes. “I think you will see less of the square, boxy shape of current skyscrapers,” Arconic’s Don Larsen says in another promo video.

Arconic skyscraper

Furthermore, Arconic hopes those skyscrapers will employ their products such as Bloomframe. This is a motorized window that transforms into a balcony in less than 60 seconds.

hofmandujardinwelcomebloomframe03tileMoreover, those windows would clean themselves—and the environment—if coated with EcoClean, an Arconic product already on the market. This titanium dioxide coating absorbs light and water vapor, activating free radicals (the atom-sized variety), which suck up and eliminate dirt as well as pollutants in the air around a building.

Will Arconic’s vision come to pass by 2062? Nobody can answer that. But the company is making a big bet on it, investing millions in advanced materials and technologies. At a time when much of the talk nationally is about fear of the future and a return to the past, Arconic’s embrace of a bright tomorrow is refreshing. So it’s no surprise we can trace the roots of this campaign to the audacious tower that rose over Seattle to celebrate and imagine the 21st century, back in 1962.

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.

Our preference for detail? It’s by design

The case for basing buildings on biometrics

A developer caused a minor uproar late last month when he criticized the Boston Seaport’s “uninspiring architecture.” Of course, it’s common for ordinary citizens across the country to air complaints about plain, boxy towers—for example, Curbed readers rated their choices for the ugliest buildings in San Francisco and New York. But in the February incident, an audience of architects found it jarring to hear an industry insider speak ill of their work.

Yet nobody seemed to notice back in November when architect Ann Sussman made even stronger comments about the corridors of glass boxes built lately in the Seaport, which is sometimes called the Innovation District. People just don’t like sheer walls, Sussman said in a talk at last fall’s ABX conference. “That’s one reason why the Innovation District fails. Too many blank facades.” The district’s streetscape even poses a “health issue,” she said. “Our cortisol level goes up” in such bland environments.

Maybe builders and designers should start paying attention to this argument. Sussman wasn’t merely expressing an opinion. A growing body of research suggests that humans are hard-wired to prefer lush details over clean lines, thanks to millennia of evolution in the wild. And Sussman says there’s nothing architects can do about that preference, except design to it.

Mind over matter

When she lived in Paris for a time, amidst the Mansard roofs and street-level cafés, Sussman noticed that her fellow visiting Americans walked everywhere. Back in the States, the same people would rather drive everywhere. She began to wonder: Why is that, really?

Sussmann sought real data on why people seem to prefer some kinds of buildings over others. Last year, relying on biometric-measuring software, Sussmann and co-researcher Justin Hollander analyzed eye movements and unconscious response to a variety of images. Their findings were eye-opening.

In one test, two sets of volunteers were shown two different photos of the Stapleton Library in Staten Island, New York—one with the windows Photoshopped out, and one unretouched. See the images side by side below. The dots indicate what parts of the building one subject looked at in each. (The human eye can make four to five rapid movements between fixation points per second.) Notice that the de-windowed walls got hardly a glance.

Stapleton Library

The researchers found the same preference in test after test. Subjects barely registered the blank or sheer walls of a library in Queens and a museum in Brooklyn, focusing instead on billboards, cars, and pedestrians.

This raises two immediate questions: First, how the heck does the eye-tracking software work? And why do people unconsciously avert their gaze from plain facades?

Programs that measure people’s reactions to images have been around for years, Sussman pointed out in her ABX talk and in a later e-mail exchange. At multi-billion-dollar companies, the designers of packaging and automobiles use the insights they gain from biometric testing to determine a look that will have mass appeal.

Fortunately, the cost of such software has come down recently, to the point where curious architects can get in on this research. For her study, Sussman used a program called iMotions to measure eye movement as well as facial recognition—e.g., picking up on our barely perceptible lip and forehead movements that indicate joy, fear, or surprise. (Other features of iMotions include tools to measure heartbeat and electromagnetic activity in the brain.)

As a test subject looks at an image on a computer, an infrared light shines on her eye. A high-resolution camera records the eye’s rapid movements, capturing the flashes of infrared as the light bounces off the eye. If the eye is looking up and to the left, a burst of red will appear on the lower right part of the eye. (At least, that’s the broad-strokes explanation.) That data is linked to the photo being shown, and the software spits out a graphic representation. For example, the below video shows the gaze path of one subject viewing an image of the Villa Rotunda in Italy.

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High tech, low bar

No learning curve with these AEC innovations

Your workload is big enough already. You don’t want to spend a lot of time learning how to use a new tool. Of course, the up-front investment of time should translate into time savings down the road. Yet the reluctance to learn something new, along with other factors, can pose a big barrier to tech adoption.

So it’s welcome news when an innovation promises to improve practices or workflow without requiring a day to figure out how to use it. In that vein, we take a look at some new products with potential. These advances in familiar technology aim to improve upon things you already use, whether in the office, trailer, or job site.

A VR vision, easy to view

“For a technology to crack the mainstream,” wrote the New York Times in January, “there is an unspoken understanding: It shouldn’t make the people who use it want to throw up.” And yet, the Times reported, at the International CES trade show in Las Vegas, the presenters of one 3D headset made barf bags available to users, just in case. It seems that wearing virtual reality goggles can be not only disorienting but sometimes literally nauseating.

A new app called Building Conversation removes these barriers by putting virtual and augmented reality on a tablet or smart phone. Imagine an architect and a developer standing at the edge of an empty lot. The architect simply hands over an iPad; the developer aims it at the site; and a 3D vision of the tower appears on the screen, overlaid atop the real-life view. If their meeting takes place instead in a boardroom, the tablet can be pointed at the table, where, through the screen, a holographic model of the building appears. A contractor and subcontractor can use the app to virtually walk through a model of the building. In whichever mode users select, they can pan through or around the image as they move. No goggles—or barf bag—required.

There’s less of a “wow” factor than with an immersive headset, but the image is clear enough and the ease of use can’t be beat. Plus, by allowing stakeholders to literally share the vision, passing the tablet back and forth and looking at the same 3D image together, this twist on VR/AR technology brings back the human interaction that is essential in project development.

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Throwback Thursday: Proof testing bridges with living subjects

It sounds crazy now. In an era when iron bridges routinely collapsed under the weight of marching soldiers, the builders of a high-profile exhibit hall chose to prove the sturdiness of their elevated iron walkways by . . . marching soldiers across one. And running them across it. Oh, and having 300 construction workers jump up and down on it, in unison, “for some time.”

Why did they think this was a good idea? And what was the result?

To illuminate this historical nugget, we spoke with Henry Petroski, an expert in failure analysis. A professor of civil engineering and history at Duke University, Petroski included the anecdote in his book To Engineer is Human: The Role of Failure in Successful Design.

A cathedral to progress . . . but would it hold up?

To be clear, the exhibit hall in question was quite innovative in many ways. The Crystal Palace (below) housed the first World’s Fair, in London in 1851. Its soaring glass-and-iron design was like nothing ever seen then. (Almost a horizontal skyscraper, it continues to influence design today.) Cutting-edge tools such as circular saws and steam-driven drills were used in the palace’s construction.

crystal_palace_-_interiorBut as impressive as the Crystal Palace appeared, contemporary Britons raised questions about the strength and stability of the temporary structure, especially its elevated walkways. “After all, during this time iron railway bridges were failing at a rate of almost one in four, and suspension bridges were collapsing under marching soldiers,” wrote Petroski. “The safety of the Crystal Palace galleries had yet to be demonstrated.”

And so, “a 24-foot-square section of gallery was constructed just off the floor on four cast-iron girders,” Petroski wrote. Queen Victoria and the press were invited to witness a proof test. The project’s 300 tradesmen and laborers were assembled, along with a company of sappers and miners (the British military’s engineering corps).

Let’s pause here a moment. Petroski has studied design failure for decades, and he has many thoughts on pedestrian walkways. “I think they’re not taken as seriously, perhaps, as they should be, because the load is considered lighter” than vehicles, he told us. “But when you jam people shoulder-to-shoulder on every square foot of a bridge,” as happened, for example, during the 50th anniversary celebration on San Francisco’s Golden Gate Bridge in 1987, “it’s actually far heavier even than bumper-to-bumper [auto] traffic.” In that case, he said, “the bridge visibly sagged in the middle.”

As to the temporary walkways inside the Crystal Palace in 1851, here’s what happened, according to the London Illustrated News:

The first experiment was that of placing a dead load of about 42,000 lb., consisting of 300 of the workmen of the contractors, on the floor and the adjoining approaches.

The second test was that of crowding the men together in the smallest possible space; but in neither case was there any appreciable effect produced in the shape of deflexion. So much for dead weight.

The third experiment—which was that of a moving load of 42,000 lb. in different conditions—consisted in the same party of workmen walking first in regular step, then in irregular step, and afterwards running over the floor, the result of which was equally satisfactory.

The fourth experiment—and that which may be considered the most severe test which could possibly be applied, considering the use to be made of the gallery floors when the Exhibition is opened to the public—was that of packing closely the same load of men, and causing them to jump up and down together for some time: the greatest amount of deflexion was found to be not more than a quarter of an inch at any interval.

The third experiment was then repeated, substituting, however, the Sappers and Miners engaged at the works, for the workmen of Messrs. Fox, Henderson, and Co.; and this last trial, which was quite as satisfactory as the others to all present, is represented in our illustration [below].

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Girding for success

So the walkway held up. How had the palace’s structural engineers been so sure they would avoid embarrassment—and their men would avoid injury—in the presence of their queen and London’s reporters?

As it turns out, the engineering team had tested, individually, all cast-iron girders to be used in the palace and walkways, with a brand-new machine invented specifically for the project. “The ordinary means of testing girders, by loading them with weights, would have occupied far too much time,” according to the fair’s official chronicle. A Mr. C.H. Wild devised “an ingenious apparatus” to accomplish the task in a few minutes (per girder).

hydraulic-pressWild’s apparatus (above) built upon technology developed by Joseph Bramah in the 18th century, and prefigured today’s universal testing machines. It was a hydraulic press that used pistons to squeeze girders “precisely at those points, and in the same manner, as the load from the gallery or the roof would do.” Using the press, Paxton’s engineers calculated that the gallery girders would withstand a pressure of 15 tons, while they estimated that the girders would only be subject to a pressure of 7.5 tons.

Making a circus out of it

The proof test with the jumping and the sappers and miners, then, was done largely for the benefit of the press, said Petroski. And if that sounds risky, get a load of this: “Sometimes bridge designers would walk elephants across them,” Petroski said. For example, in 1874, a test elephant lumbered across the Eads Bridge, over the Mississippi at St. Louis. A decade later, the famous Jumbo did the honors at the Brooklyn Bridge. “It was a mixture of publicity and practicality and superstition.”

The more common way to test bridges back then evokes a classic Calvin and Hobbes strip.  “Once the structure was completed,” said Petroski, “very heavy railroad engines or something equivalent would be driven across the bridge to, quote-unquote, ‘prove’ it would handle the load. That’s a long tradition in bridge-building. And in fact, in Eastern Europe, the engineer who designed the bridge would stand under it—sometimes even with his family—to show this was a solid design that he had all the confidence in the world about.”

But lest you think such stunts are wholly outdated, Petroski pointed to the Millennium Bridge in London. The pedestrian bridge across the Thames opened in June 2000. It swayed noticeably, and was closed three days later. After shoring up the bridge, engineers held a successful test with a hundred volunteers walking over it in 2002.

Lock and load

Nevertheless, in 2017, you probably won’t see human (or elephantine) subjects proof-testing a new structure. Today’s engineers test individual girders and other structural elements before assembly and use the results to calculate the maximum load—as the Crystal Palace team did. But if the public demanded further proof after assembly nowadays, engineers would conduct a load test with simulated human weight.

“They often do ‘drop tests’ with elevators,” said Suffolk Northeast Regional Safety Director Martin Leik, “to test that they can handle the weights they are to be loaded with when in full use.” These are “artificial weights,” noted Leik. “No one would even think about using real human beings for something like this now.”

Well, that is a relief. You might even call it a weight off the shoulders.

Final note: want to learn more about failing bridges? Petroski’s latest book, The Road Taken: The History and Future of America’s Infrastructure, was just released in paperback last week. It’s more timely than ever now.

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.

Can you tell which roof has hidden solar panels?

Would you believe all of them? Meet integrated rooftop solar.

In the dark of winter, when days are shortest, those of us in northern climes long for the sun. What better time to think about capturing and storing that sun’s energy? Solar electric power has been around for decades, and advances in the technology keep making it more efficient and practical. But for many, the desire to cut the household carbon footprint is tempered by aesthetic concerns. Rooftop solar panels don’t exactly look pretty, unless you’re going for Wall-E-meets-Windows chic.

Enter Tesla Motors. Not just a car company anymore, Tesla recently acquired SolarCity, the nation’s largest solar service provider. And the combo’s flagship product? A solar roof. It’s an array of photovoltaic panels, custom installed, that looks pretty much just like an ordinary roof. It will come in styles including slate and Tuscan tile. And with the star power of CEO Elon Musk, this product with curb appeal just might do for solar rooftop panels what Tesla has done for electric cars—make them cool. All part of the company’s professed mission: to accelerate the world’s transition to sustainable energy.

Musk unveiled the roof last fall at a shareholders’ meeting held in Universal Studios’ backlot. Investors gathered on a street that has served as the generic suburban setting for TV fare from Leave it to Beaver to Desperate Housewives. To hit the market some time this year, the panels are printed with the shingle-looking designs in a process called hydrographic coloring. They’re made of exceptionally durable tempered quartz glass. See how the material holds up compared to conventional roofing tiles:

Hidden underneath the glass are photovoltaic cells that will harvest the sun’s rays, feeding the energy to Tesla’s Powerwall 2 battery. The company says the battery can power an average two-bedroom home for a full day.

“It looks viable,” said Josh Rollins, LEED AP BD+C. “If it is, it’s a total game-changer.” A senior manager of marketing at Suffolk Construction, Rollins is also a leading member of the company’s Green Committee. “Elon Musk reminds me a bit of Steve Jobs in the way that he hypes his products, but this one is particularly exciting for anyone who’s passionate about reducing their carbon footprint,” Rollins said.

Musk’s presentation lacked some details, but flurries of informed speculation on the part of industry professionals help fill in the blanks. The biggest question to many is the roof’s cost. Musk says Tesla’s system will be cheaper than a traditional roof, when you factor in projected savings on your utility bill over the Tesla roof’s lifetime (50 years).

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Image courtesy of Tesla

How could Tesla achieve that lower price tag? For one thing, the quartz glass is a fifth as heavy as typical roofing materials; meaning lower shipping costs. For another, Musk hinted that he’ll cut out middlemen in the current roofing supply chain, with Tesla doing the installations itself.

All that said, the cost of a traditional roof plus the cost of grid electricity is quite steep, so even a figure smaller than that sum will likely still be large. Consumer Reports put the total as high as $70,000, too much for many homeowners to bear up front. Will the company offer financing? What if a homeowner defaults on the loan? Will Tesla rip the roof off and take it back? Unclear as of yet.

But Tesla’s entry into the residential solar market can only be a good thing if you’re rooting for the environment. As many as five million roofs per year need to be replaced. If you need a new roof anyway, why not make it one that will save you money on utilities? At least a certain segment of homeowners will be able to afford the premium Tesla product. And for those who can’t, Tesla’s announcement should bring more attention to other, relatively affordable integrated rooftop solar products.

That’s right, Tesla has competitors in this niche—companies like SunTegra and CertainTeed. Though none of their solar products are quite as invisible as Tesla’s, many are pretty darn unobtrusive, especially compared to the standard rack-mounted panels. (Check out the examples below.) These companies welcome the new publicity. “I have to agree with Elon Musk: the future for roof integrated solar is bright,” wrote SunTegra CEO Oliver Koehler in a trade publication. “It’s going to be an exciting next couple of years.”

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Image courtesy of CertainTeed

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Image courtesy of SunTegra

What we really look forward to is learning whether the integrated technology can be scaled up to apartment complexes, and perhaps to even bigger projects—maybe even high-rises. After all, said Rollins, “Why stop at the roof?” Rollins recalled a previous Build Smart blog post about harnessing solar energy with windows, something a skyscraper in Australia plans to do. “Why not cover the skin of the entire building in solar panels? That’s another whole surface area that could be generating electricity,” Rollins said.

Perhaps we can yet break our addiction to supply-limited fossil fuels, thanks in part to visionaries such as Musk. Heck, the last time a Tesla release made us this optimistic, it was an awesome late-1980s power ballad. Here’s to solar finding a way.

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.