Exoskeleton tower rises in downtown Miami
Every week, a ship leaves Dubai loaded with an entire floor's worth of structural pieces bound for what's likely the most unusual, not to say outlandish, tower ever erected in Miami — One Thousand Museum, one of the last designs from the late superstar architect Zaha Hadid.
The pieces, made of a lightweight concrete reinforced with glass fiber, form the sinuous skeleton that coils up along the exterior of the tower like Jack’s beanstalk or the bones of an alien life form. The assembly of the bones is an intricately coreographed operation of daunting precision, using a construction technique that’s not been tried before.
Once it’s finished, sometime in 2018, One Thousand Museum will be, to the best of anyone’s knowledge, only the second exoskeleton tower in Miami — that is, one in which structural supports lie outside of the building’s skin, like the skeleton of an insect or a crustacean. The One Thousand Museum exoskeleton permits expansive interiors uninterrupted by columns and broad terraces spanning a jaw-dropping 40 feet that jut from the tower’s corners, giving the building a serrated edge.
“Hadid didn’t just design a cool building,” said One Thousand Museum co-developer Kevin Venger. “This side of the world has never seen a building quite like this.”
The key to its construction lies in the use of the prefabricated pieces made from a material known as glass fiber-reinforced concrete, which is typically used as decorative facing. The One Thousand Museum builders opted instead to use GFRC as a mold that’s clamped together around steel rebar. Concrete is poured inside to form a light but super-strong structure of exacting precision.
The novel approach will shave six months off the construction schedule, according to Venger. The precisely shaped GFRC panels, which remain in place, unpainted, after the concrete is poured, also produce a fine, smooth surface that would not have been possible with the use of traditional plywood molds.
Just as significantly, Venger said, the technique means that Hadid’s muscular design — which he and his partners plainly hope will become a symbol of the emerging new Miami — will be translated not into mere decoration but into functional, structural sinew.
“We wanted this fusion of architecture and structure, like something that’s been excavated, something that’s been sculpted,” said Chris Lepine, project architect at Zaha Hadid Architects.
Hadid, who was based in London, died suddenly last year in Miami Beach, where she had a winter home. The first female winner of the Pritzker Prize, architecture’s equivalent of the Nobel, she was famous for innovative structures, designed with the aid of computers, that seem to flow like lava. Though her firm goes on, One Thousand Museum is one of the last buildings Hadid had a direct hand in.
Translating Hadid’s designs from computer to built structure is widely known to be no easy thing, said Irtishad Ahmad, a civil and structural engineer who is director of Florida International University’s school of construction.
“Zaha Hadid is known for exceptional architectural designs which always pose challenges to structural engineers and constructors, for sure,” said Ahmad, who is not involved in the project.
In a typical exoskeleton building, Ahmad said, the core takes most of the tower’s load while a rectilinear exterior structure acts as bracing, making it possible to dispense with interior columns. But One Thousand Museum’s undulating structural shapes make Hadid’s exoskeleton unusually complex, and the way the builders are deploying GFRC to “mitigate” its challenge is unique, he said.
“It’s beautiful,” Ahmad said of the result.
Only one other previously built exoskeleton tower exists in Miami: Not by coincidence, it’s two doors down from One Thousand Museum on Biscayne Boulevard. Ten Museum Park, developed by One Thousand Museum co-developer Greg Covin and designed by Miami architect Chad Oppenheim, features a grid-like, rectilinear exterior structure.
Figuring out how to build Hadid’s design, in which the skeleton varies widely in shape and thickness, Venger said, was a particular challenge. At first his team considered a purely cosmetic interpretation of the bones, but then set to exploring how to make them real, with the collaboration of contractor Plaza Construction and DeSimone Engineering Consultants.
“We went through every iteration of material and process — steel, exposed concrete, pouring concrete in place,” Venger said. “None of them achieved the finish that we all felt this exoskeleton deserved.”
One issue: The concrete trade in Miami is not known for fine or precise work, and the developers and architects didn’t want imperfections. They needed the structure to look silky and flowing, as if it had been extruded from a Mr. Softee ice-cream machine.
Finally they settled on GFRC panels to be made by a company called Radiant Profile in Dubai, in the United Arab Emirates, and came up with the idea of making the pieces an integral part of the skeleton. They used three-dimensional computerized models to design each of more than 3,000 pieces within millimeters of tolerance, Venger said.
“We could otherwise never get to this accuracy that they can get to,” he said. “This way, we know that everything will line up perfectly.”
Up to the 15th floor of the 62-story tower, columns were formed in the traditional way and prefab panels were used as cladding only. That’s because the columns are so thick to that point that they require as many as eight panels to enclose them completely — too many to hold together safely given the heavy tonnage of rebar and concrete needed for support, Venger said.
The Dubai factory turns out the pieces in a precise order, bottom to top, after which they’re nestled in cradles and loaded on ships that take about 42 days to reach PortMiami. They’re then trucked to a storage yard in Northwest Miami-Dade that holds up to eight floors worth of pieces at a time, so that there is no issue if a ship is delayed. The wrapped pieces are stored in the open in special cradles.
When needed, the panels are transported to a prep yard two blocks from the tower’s Biscayne Boulevard site and, once readied, taken to the tower and hoisted into place by crane. There, two pieces are clamped together around rebar and concrete is poured into the assembly. Progress is rapid, at about a floor per week. By the end of February, construction was just past the midway point, at 34 stories.
Other prominent exoskeleton buildings
▪ John Hanckock Center, Chicago; designed by Skidmore, Owings & Merrill (SOM)
▪ Oakland Coliseum (Oracle Arena), Oakland, Calif.: designed by SOM
▪ Alcoa Building, San Francisco: designed by SOM
▪ Macau Hotel, Macau, China: designed by Zaha Hadid Architects
▪ NEO Bankside, London: designed by Richard Rogers
▪ Pompidou Center museum, Paris: designed by Rogers and Renzo Piano
▪ World Trade Center, New York: designed by Minoru Yamasaki