The Exoskeleton: an empirical investigation into a bottom-up approach to structural design

As a part of their master dissertation, Thibaut Van Dousselaere and Silke Van Geeteruyen investigated a ‘bottom-up’ approach to structural design by means of prototyping, a subcategory of digital fabrication. The design of a small pavilion, the Exoskeleton, served as a test case. The Exoskeleton is a pavilion that shows how Computer Aided Manufacturing can create rapid prototypes. This manufacturing process also allows for real-scale construction and experimentation with limited resources. In this project, a system of modules, designed with different dimensions, is put together with simple joints without nails or screws. This allows for different surfaces to be formed and for the pieces to be rotated and assembled at various angles and heights.

The ‘bottom-up’ approach allowed the students to work in an empirical way; with new ideas being validated through immediate physical testing of their constructional behavior. In this way the total design does not arise from an overarching 3D-model, deriving components from the overall shape, but instead from an iterative design process, whereby first the components and only then the overall shape is determined through prototyping. Applying this bottom-up approach to structural design enables a detachment from well-defined structural typologies. Since knowledge is gradually built up during the design process, this approach enabled them to investigate innovative structural principles or a new application of a certain material. A hands-on understanding of the structural behavior of a certain construction was also developed during the design process.

Computer Aided Manufacturing was instrumental to this approach, as it allowed for rapid fabrication of numerous prototypes. This rapid prototyping method enabled them to quickly test and learn. Making the design process affordable, was only possible if the materials used for the physical models were cheap and the fabrication techniques were fast. Hence limitations concerning budget and availability of fabrication techniques were taken into account from the start of the design process itself. Thin plywood panels were chosen as material, and 2D CNC-techniques (laser-cutting and milling) as form process. An investigation into the characteristics and physical behavior of the material is ongoing, since this bottom-up design process starts from the possibilities that lie within the material itself.

Applying a bottom up design approach, the students did succeed to investigate the innovative structural principle of active bending. Active bending refers to the systemized elastic deformation of a certain material, as a form-giving and self-stabilizing strategy for static structures. Handling this bottom up approach, it was possible to build a pavilion demonstrating this innovative structural principle in a short time-span, using only limited resources. As a consequence of the bottom up design approach, they designed a parametric system rather than a single pavilion. By applying the same assembly system to the designed modules with varying dimensions, different surfaces can be generated.

Only two types of connections were used in the pavilion: sliding joints and tie straps. The sliding joints are a straightforward and elegant solution to connect the panels on the inside of the pavilion to those located on the outside (and the other way around). Since the panels are actively bent, the resilience force in the panels plugs them into the sliding joints. As such, these joints are very simple, no attached parts such as nails or screws needed. Tie straps are used to keep the panels in their bent position. Tie straps enable a fast and easy assembly, but they also serve as an important control mechanism.

During construction, the more panels that are assembled, the higher the pavilion rises and the closer it gets to its final shape. It was thus necessary to have a connection that could be gradually tightened during construction. Tie straps provided the ideal solution given that all panels could be bent just as far as needed and the straps could be tightened further as the pavilion rises. Overall, the objective was to build a structurally challenging pavilion that is digitally fabricated, in a limited time span and using only limited resources. This makes the pavilion accessible for everyone with access to a fablab, since the pavilion does not rely on complicated digital fabrication techniques.

In addition, specific targets were being put forward for the design of the pavilion itself. First of all, the amount of resources necessary to assemble and construct the overall pavilion should be as limited as possible. This decreases the total cost and creates an affordable pavilion. Also, the pavilion was meant to be assembled by hand and with easy disassembly being a possibility. Lastly, only materials and fabrication techniques that are widely available should be used, making the assembly of this pavilion accessible to a large group of people.

Technology has changed the way everything is done, even in the world of architecture. The Exoskeleton is a unique design that was not only inspired by technology, but also built with the help of technology. A closer look at the finished product reveals that the objective of their research has been accomplished. In a limited span of time and with limited resources, the students were able to design and construct a full-scale pavilion as a case study to evaluate a bottom up approach to structural design. More importantly, their work lays the ground for further development and potentially application in the real world.

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