Citation: Limb, a Fantastical Take on Timber Construction

“This project reinterpets a very natural organic form through digital fabrication technology to create new shapes that retain the same sense of tree members, but go beyond that.” —Juror Tom Chung, AIA

Sometimes the best innovations are hidden in plain sight—or in the pages of an 18th-century how-to manual for France’s navy. Such is the case with Limb, a project inspired by the lost art of using tree crotches in lieu of traditional woodworking joints that is detailed in Encyclopédie Méthodique: Marine.

“I have been looking at pre-electric technologies for a while, and what impressed me was the ways that people managed to be very innovative with the materials they had at hand,” says Steven Mankouche, head of Ann Arbor, Mich.–based Archolab and an associate professor of architecture at the University of Michigan (U-M).

Because the crotches—the connection points between a trunk and a limb, or between a main limb and an offshoot—are a single integrated piece, they are stronger than a joint that forces together disparate vertical and horizontal members. “Shipbuilders in particular liked to use tree crotches as joints,” Mankouche says. “Especially in a sea battle, you don’t want your joinery to fail.”

Once Mankouche became aware of tree crotches, he started seeing them everywhere—in construction, furniture, and more. “I was so impressed with the joinery,” he says of historical farm buildings. “These barns last forever.” Furniture makers, meanwhile, prized such elements for their ability to provide function without drawing attention to the joint.

But precisely because they are organic in nature, tree crotches are hard to replicate, and their use in construction fell off during the Industrial Revolution, which required uniform components for mass manufacturing.

Most large trees have several crotches but, because of the joints’ density and complicated grain pattern, they often end up in landfills. Mankouche with fellow researchers and U-M colleagues Peter von Bülow and Kasey Vliet wondered whether they had a place in 21st-century design.

His first insight was that while every crotch is a little different, most fall within a narrow range of angles—between 20 and 60 degrees— particularly once they have been milled. He and his team then built a database of hundreds of the most commonly found angles. “A lot of digital work is focused on customization,” he says. “The idea here is to have a vocabulary of components.”

In practice, an architect using the database would collect a set of tree crotches and then input their angles into their database. An algorithm would then crunch the values into an optimal arrangement for whatever structure the user wants to build. “Our project reduces a number of common angular occurrences, within unique limb bifurcations, down to a set of shared parts that can be ‘tuned’ to and reused in different structural systems,” Mankouche and his team describe in their submission.

As a start, the team has identified four potential forms of increasing scale—a frame, a column, a shell, and a semi-rectangular structure they call a “hedge”—and designed prototypes for each, as a demonstration of what the database can do.

Limb, Mankouche stresses, is not about mimicking nature, but rather about drawing on its genius for efficient, strong construction.

Project Credits
Project: Limb
Design Team: Archolab, Ann Arbor, Mich. . Steven Mankouche; University of Michigan Taubman College of Architecture and Urban Planning . Peter von Bülow; Kase Studio, Ann Arbor, Mich. . Kasey Vliet
Research Assistants/Partners: Robert Allsop, Kevin Bukowski, Cody Gilman, Andrew Thompson, Omid Torghabehi, Benjamin Wichman, Shaobo Niu
Funding: University of Michigan Taubman College, University of Michigan Office of Research
Special Thanks: 2017–2018 Taubman College’s Research Through Making grant

Note: This story has been updated since first publication.

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