New MIT system using discarded tree forks for use in load-bearing structures

Wood is becoming an increasingly popular building material, but wood is mostly harvested from the long, straight trunks of trees. In an effort to reduce waste, a team at MIT has developed a method to also use bearing seals in shafts.

Led by Associate Professor Caitlin Mueller, the researchers began by collecting pieces of scrap wood from a cluster of previously felled trees in the town of Somerville, Massachusetts.

Scientists have been particularly interested in Y-shaped forks in which the trunk or a large branch splits in two. Normally, these parts are crushed or burned.

Shaft forks are naturally designed structural connections that function as cantilevers on shafts, meaning they have the potential to transfer force very efficiently due to their internal fibrous structure.

If we take a tree fork and cut it in half, we see an amazing network of fibers that intertwine to create these often three-dimensional load transfer points on a tree. We are starting to do the same with 3D printing, but we are far from what nature does.

Caitlin Muller

Once the scientists had a good collection of hairpins, they 3D scanned each one, then added their digital model to a database.

Using what is known as the Hungarian algorithm, it was then possible to determine which forks from this database would best meet the load requirements of a specific Y-shaped node, where two straight pieces of material join together to support a load, to a man-made concrete structure.

The system could also work the other way around, showing how other aspects of a structure should be modified to use a certain tree branch for a specific node.

In the next step of the process, another algorithm was used to guide the robotic cutting of the selected forks so they could better fit and support the load of their respective nodes. Finally, a computer model guided the team through the assembly process, showing which forks went to which node.

Although it may be some time before we see an actual building constructed with this technology, Mueller and his colleagues constructed a test wooden sculpture that has been displayed on the MIT campus.

Because they’ve been delayed by the pandemic, the piece remains a work in progress: it currently incorporates 12 tree fork nodes, but should eventually include around 40. It will be installed in Somerville, where the donor trees grew.


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