TrussFab: creating large-scale structures from PET bottles
There are many materials available that are made from recycled plastic bottles, or even projects using them as a whole in an attempt to combat the plastic waste problem. PET bottles can be very sturdy when used right, creating new construction possibilities. To make it easier for even non-engineers to build with plastic bottles, a team from the Human Computer Interaction Lab at the Hasso Plattner Institute in Potsdam, Germany, created TrussFab, an end-to-end plugin for Sketchup.
In other systems, the bottles are considered as if they were bricks, but TrussFab sees them as beams. To form structurally sound node links, the bottles are used in triangles, also known as trusses. Freestanding bottle constructions tend to break easily, but in triangle structures, this is not the case. Plastic bottles buckle easily when pushed from the side, whereas they are very strong when pushed or pulled along the main axis. Trusses turn lateral forces (bending moments) into tension and compression forces along the length of the edges, creating structures that can hold a lot of weight.
The programme is available as a plugin to Sketchup. It does the engineering for you, so that even non-engineers can use it to build structures from PET bottles. TrussFab offers primitives as building blocks in tetrahedron and octahedron shapes. The initial shapes can be manipulated, and the programme adjusts the model in a way that automatically maintains the truss structure and the overall structural stability. It is also possible to convert an existing 3D model automatically in a structure made from bottles.
To build the structures, the system designs and generates connections to connect the bottle openings together. These connection hubs can be 3D printed or, in case of 2D constructions such as façades, laser-cut.
The programme designs constructions with ‘beams’ made from two bottles connected at the bottom. These bottoms can be connected with, for example, dowel screws, but a downside to this is that this damages the bottle. Non-destructive methods to connect the bottles include using tape, rope or shrink tubes.
When the hubs and beams are ready, the designer can construct the structure.
To test their own system, the team designed and fabricated tables and chairs, a 2.5 metre (8.2 feet) bridge strong enough to carry a human, and a 5 metre (16.4 feet) high pavilion, consisting of 1,280 bottles and 191 3D printed hubs, presented at CHI 2017 in Denver, as you can see in the video below.
Photos: Hasso Plattner Institute