MIT system assigns unwanted tree forks to use in load-bearing structures
Wood is becoming an increasingly popular building material, but the timber is harvested mainly just from the long, straight trunks of trees. Aiming to reduce waste, an MIT team has developed a method of also using a tree's load-bearing junctions.
Led by Assoc. Prof. Caitlin Mueller, the researchers started by collecting sections of waste wood from a group of trees that had already been cut down in the city of Somerville, Massachusetts. The scientists were specifically interested in the Y-shaped forks where the trunk or a large branch divides in two. Ordinarily, such parts are just chipped into mulch or burned.
"Tree forks are naturally engineered structural connections that work as cantilevers in trees, which means that they have the potential to transfer force very efficiently thanks to their internal fiber structure," said Mueller. "If you take a tree fork and slice it down the middle, you see an unbelievable network of fibers that are intertwining to create these often three-dimensional load transfer points in a tree. We’re starting to do the same thing using 3D printing, but we’re nowhere near what nature does."
Once the scientists had a good collection of forks, they proceed to 3D-scan each one, then add its digital model to a database. Utilizing what's known as a Hungarian algorithm, it was subsequently possible to determine which forks within that database would best meet the load-bearing requirements of a specific Y-shaped node – where two straight pieces of material come together to support a load – in a particular human-made structure.
The system could also work in reverse, showing how other aspects of a structure should be altered in order to utilize a given tree fork 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 were able to best fit into and bear the load of their respective node locations. Finally, a computer model guided the team through the assembly process, showing which forks were intended for which nodes.
Although it may be some time before we see an actual building constructed using the technology, Mueller and colleagues did build a proof-of-concept wooden sculpture which was displayed on the MIT campus. Because they were delayed by the pandemic, the piece is still a work in progress – it presently incorporates 12 tree-fork nodes, but should ultimately include approximately 40. It will then be installed in Somerville, at the site where the donor trees once grew.