HygroShape: Self-Shaping Structures from ICD/ITKE

The projects introduced in this post are from ICD and ITKE, Both institutes are in the university of Stuttgart in Germany. ICD’s Research and teaching are in the field of computational design and computer-aided manufacturing in architecture. Research and teaching at the ITKE focus on the integration of structural design and architecture.

[Some of the Computation design projects in these institutes.]

The first project is named hygro-shape, which is self-shaping wood furniture.

In this project, the furniture pieces are produced in physically programmed flatpack configurations, to shape themselves when unpacked. The project represents a shift in design and manufacturing processes by using material programming.

[HygroShape – Self-shaping wood furniture]

The project uses the natural, intrinsic properties of wood. This self-shaping emerges from the hygroscopic shrinkage that naturally occurs in wood.

Hygroscopy is the phenomenon of attracting and holding water molecules from the surrounding environment, which is usually at normal or room temperature. Wood shrinks and swells the greatest amount in the tangential direction, about half as much in the radial direction, and a very very small amount in the longitudinal direction. On the other hand, wood has a unique fibrous composite composition of the cell walls which is stronger along the grains than across them. So, The HygroShape concept is based on the utilization of hygroscopic shrinkage that occurs in wood materials after they are harvested and equalized with the surrounding environment.

In timber construction, moisture typically causes problems with cracking and deformation; so, when moisture changes, the stress development must be carefully controlled. In contrast, in this project wood is programmed and arranged in a way to utilize this powerful, naturally occurring deformation to trigger a self-shaping behavior.

Freshly cut timber comes naturally with a high water content. If obtained directly, the wood can be processed and prepared in a way to maintain that high moisture content during cutting and other steps.

In this research, highly tuned computational design methods, and physical and mechanical material characteristics are digitized and used for calculating specific material syntax to direct the material toward a designed shaping sequence. The computational design tool is used to uniquely arrange the boards in tailored layups in a way that will result in the final expected curved geometry. In site, a simple exposure of the pieces to usual indoor climates induces natural drying as the wood material equalizes with its environment and smoothly shapes itself. The outer layers with longitudinal direction will have smaller deformation because of lower shrinkage, on the other hand, wood is stronger along the grain.

After shrinkage and shaping the final geometry, the volume will increase about 30-fold. It happens effortlessly, in silence, without human interaction, tools, or assembly instructions, and as quickly as overnight. It is also interesting to mention that methods of bending wood into different shapes for structure and aesthetics have existed for centuries, but they still mostly rely on the brute mechanical force for the shaping process. However, besides a shift in design thinking, new computational simulations for more accurate prediction, now allow us to use the moisture-induced swelling and shrinking to design and program self-shaping movements at a larger and larger scale.

The larger scale experience with the self-shaping design is explored in the 14 meters tall Urbach Tower, designed and manufactured in a flat state and transformed autonomously into the final, programmed curved shapes. But, contrary to the previous project, here, the flat (CLT) components transform during the industry-standard technical drying process.

Here is the manufacturing process: The structure consists of 12 components made entirely from cross-laminated timber of spruce wood boards sourced regionally from Switzerland. The components are 5-Axis CNC cut and detailed with precise curvature and optimal fiber alignment from the manufacturing process, each component is cut in detail in just 90 minutes of machine time. Individual components span up to 15 m with a thickness of only 9 cm. Manufactured with a high wood moisture content and specific layups. When removed from the drying chamber the parts are precisely curved. The inherent curvature of the whole structure enables a highly slender and lightweight tower structure. A custom-made protective cladding layer consisting of glue-laminated larch wood is added on the outside. This also includes the application of a transparent and durable coating that protects the wood from UV radiation and fungi attack. In the assembly stage, the prefabricated assembly groups of the tower, each consisting of three curved components, were assembled in a single working day by a team of four craftsmen without the requirement of extensive scaffolding or formwork and topped off by a transparent roof. The lightweight building elements are connected by crossing screws. The tower acts as a surface-active structure through its expressive curved geometry.

[URBACH TOWER – Remstal Gartenschau 2019]

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