New book explains the secrets behind famous skyscrapers, other structures

Mar 23, 2018

Roma Agrawal spends a lot of time thinking of the sheer power of concrete. She’s a structural engineer who helped design The Shard in London, an iconic 95-story skyscraper that opened in 2012.

“What I really like about it is that it has so many different forms,” Agrawal says. “It's quite an indeterminate material … I just love the fact that it can be anything you want it to be."

Agrawal’s recently released book, “Built: The Hidden Stories our Structures,” provides insight on how skyscrapers like The Shard are constructed and other fascinating tidbits behind iconic buildings and structures across the globe. And yes, the book includes an ode to concrete and the Romans’ mastery of the building material.

It was the Romans who developed a type of concrete using a specific volcanic ash that could dry underwater. The mixture of concrete and ash did not need air for the final solidification stage.

“The Romans had, I think, this amazingly can-do attitude about construction as well. And they just built. They built big. They built complicated. They tried new materials that were really, really experimental,” says Agrawal, whose favorite structure in the world — or at least one of them — is the Pantheon.

Every large structure comes with its challenges. With The Shard, the biggest obstacle was its location on the banks of the River Thames next to London Bridge. Compared to a city like New York City, built atop Manhattan’s strong bedrock, the land underneath The Shard is composed of soft, wet clay. To establish a firm foundation, the solution was to install gigantic concrete piles “to basically anchor it like the tree roots do for the tree.”

Then there was the wind coming off the river.

“So we think, ‘Oh, the wind is quite harmless.’ We like a nice little breeze. But it can play havoc with skyscrapers, so we need to make sure that the buildings are stable when wind hits from all the different directions,” Agrawal says.

Another challenge comes from making sure a skyscraper’s massive weight is equally distributed so that the building’s lower levels are not crushed beneath the floors above them.

“All of this comes down to getting the right materials, so we have a lot of experience,” Agrawal says. “Now we've got computing power, so we can do a lot of mathematical analysis to understand how heavy the building itself is — but also all the stuff that's going inside the buildings: like people, like books in a library or [whatever] else. We basically crunch the numbers, and then we make sure that the base of the columns are the right material and there's enough material there to resist those forces."

Part of that analysis includes how much a building can sway without making people inside it nauseous. Agrawal says engineers generally know what level of a building's acceleration humans can perceive as it sways.

“When we do our analysis, we're looking at how much the building is moving, but more importantly, how quickly the building is moving,” she says. “We try and make sure that that movement is slower than we can really perceive, or that makes us feel nauseous."

The book also goes into detail about the Brooklyn Bridge, the suspension bridge designed by renowned architect John A. Roebling. Lesser known is the role his daughter-in-law, Emily Roebling, played in the bridge’s construction. Even though Emily Roebling was not allowed to pursue an engineering degree, given the late 1800s-era in which she lived, she managed to finish the massive project after her father-in-law died of tetanus and her husband became bedridden with what is now known as decompression sickness.

“She's such a heroine of mine… What I really particularly admire is that, not only did she learn all the technical skills you need as an engineer, but Washington Roebling, her husband, said her biggest contribution to the build was her talent as a peacemaker. And that is such an important part of engineering structures,” Agrawal says.

Construction materials used for skyscrapers and bridges has been tremendously influenced by climate change, Agrawal says. Although concrete — the most-used manmade material on the planet — has remarkable properties, it emits a substantial amount of carbon. There have been extensive efforts to make it more eco-friendly. Almost 95 percent of steel, the backbone of most large structures, can also be recycled and reused.

“When you think about buildings more broadly, we're thinking about energy consumption, because our buildings use a lot and lot of energy,” she says. “So we're also thinking about, how can we insulate them better? What kind of cladding can we use? Can we use more efficient air conditioning? There's lots of different angles that we need to look at from a building point of view."

Building cities, she adds, are "another level" of consideration. 

Agrawal hopes her book will cultivate a deeper appreciation for the immense calculations and details that go into building skyscrapers and other large structures that city dwellers may take for granted.

“I want everyone to look at our world through the eyes of an engineer. So when I go up to the viewing gallery in The Shard, for example … everyone's taking photographs of the river and of St Paul's Cathedral, but I'm looking up at the steel and I'm looking at the bolts and the welds, and I'm thinking about how I can see how it was put together,” Agrawal says.

“I feel like you should be looking for peculiar details. You should be looking for the materials, but you should also very much try and look beyond what you can actually see and try and delve deeper into our structures."

This article is based on interview on PRI’s Science Friday with Ira Flatow.

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