FROM MACHINE CONTROL TO MATERIAL PROGRAMMING SELF-SHAPING WOOD MANUFACTURING OF A HIGH PERFORMANCE CURVED CLT STRUCTURE – URBACH TOWER
Dylan Wood, Philippe Grȍnquist, Simon Bechert, Lotte Aldinger, David Riggenbach, Katharina Lehmann, Markus Rȕggeberg, Ingo Burgert, Jan Knippers, and Achim Menges
1Institute for Computational Design and Construction, University of Stuttgart
2Laboratory for Cellulose & Wood Materials, EMPA
3Institute for Building Materials, ETH Zurich
4Institute for Building Structures and Structural Design, University of Stuttgart
5Blumer Lehmann AG
The Urbach Tower, a high performance timber structure utilising self-shaping wood manufacturing for curved CLT. (Rolland Halbe).
Computational design and digital fabrication for architecture focuses increasingly on advanced robotic machine control for the shaping and assembly of pre-engineered building materials to produce structures with complex functional geometries.
Intelligent digital planning methods and machine material feedback make processes of additive, subtractive and formative manufacturing incrementally more efficient and tuneable. However, complex shaping is still achieved by combinations of pre-shaped formwork, application of brute mechanical force, robotic manipulation, and subtractive machining from larger stock.
The basic self-shaping wood manufacturing process in which curvature is generated from loss of wood moisture content in a designed bilayer structure. A sample 1.2m x 0.6mm x 40mm thick spruce wood bilayer cut from the larger production parts, shown in the flat high moisture (22 % WMC) production state and curved dry (12% WMC) actuated state (bottom). (ICD/ITKE- University of Stuttgart).
In the shaping process, powerful innate material behaviour that influences shape is either viewed as problematic or ignored. In the quest for infinitely more axes, and endlessly more sophisticated end effectors, it’s clear we have overlooked the useful capacities found within the structures and tissues of the materials we fabricate with.
Integration and upscaling of the self-shaping manufacturing process to produce high curvature CLT components for the tower structure. Bilayer design, actuation, combining/ stacking, edge finishing, and connection detailing. (ICD/ITKE- University of Stuttgart)
This research presents a paradigm shift towards a material-driven self-shaping fabrication method for full scale timber building components. Here the 3D geometry emerges from the designed material arrangement in flat 2D parts that are exposed to an external stimulus.
Completed curved CLT rohling after the stacking and combining of bilayer panels to create 5-layer, 90mm thick CLT. Shown mounted on a large scale 5-axis CNC machine used for lightly machining the edges and adding the crossing screw connection detailing.
By utilising the unique capacity of the material to act as an integrated, shaping actuator and the final loadbearing structure, elaborate external forming equipment is eliminated. This simple yet informed material programming replaces typically material, energy and labour intensive shaping process.
Using wood, which exhibits strong anisotropic dimensional instability in response to changes in moisture, we developed a material-specific predictive model, and a physical material programming routine that allows for a selfshaping manufacturing process for high curvature Cross Laminated Timber (CLT) building components.
Completed prefabrication of assembly groups prepared for transport following in the connection of three components and addition of the Larch wood façade with UVood ® surface treatment. (ICD/ ITKE- University of Stuttgart)
Surface active structures benefit tremendously from curvature in both the overall structural geometry and individual building components. For wooden shell structures, curvature is, however, expensive to produce in terms of costs, material, and environmental impact.
In this research, the manufacturability of high curvature CLT components enabled by self-shaping is paired with the development of performative geometry and structural analysis for folded plate cylindrical shell structures.
. FEA modelling of the structural design aspects for the thin shell structure. Global deformations of the structure due to wind loads (left), CLT utilisation including intra component joints (centre) and the range of connection angles for fine-tuning of crossing screen angles per building regulations and fabrication constraints (right). (ICD/ ITKE- University of Stuttgart)
The concept is demonstrated with the design, engineering, manufacture, and construction of a 14m tall thin shell tower structure. Architecturally, the tower serves as a shelter and landmark, showcasing the potentials of innovative high performance and sustainable timber construction.
On-site assembly of the prefabricated groups highlighting the slenderness of the load bearing structural CLT (90cm). (ICD/ITKEUniversity of Stuttgart).
The challenge of applying self-shaping technologies for the building industry is how to upscale basic principles to a size that is suitable for the manufacture of building components while ensuring that both material and building structure are maintained. The fundamental research question centres on how known shape-changing properties of a building material can be used purposely to generate shape.
Programming of the shape changes requires an advanced understanding of the underlying mechanisms of deformation, which can only be gained by employing simulations based on specific material models coupled with experimental testing.
Upward interior view with the locally convex curvature creating a soft billowing aesthetic from fully load bearing structural components with hidden connection details. (ICD/ITKE- University of Stuttgart).
Critical to manufacturing innovation is the development of a materially-informed digital design methodology that could be used to predict and tune the final shape and translate a design geometry to the material information required for production. To be effective, the predictive model must be accurate using material input parameters and sorting ranges that can be collected and implemented in an industrial context.
The construction of the tower demonstrated self-shaping manufacturing for industry level production of curved load-bearing building components. As the same material is both the shaping mechanism and the final structure, the need of larger machines and formwork is greatly reduced.
The current process is directly applicable for the solid wood production of lightweight curved roof components, curved vertical shear walls for multi-storey timber construction and cylindrical structures such as silos or turbine towers. It presents an ecological option for performative curved geometries that are often produced with malleable yet energy intensive materials such as concrete, plastic or metals.
The sharp edges at the intersections of the concave geometry catching the light as the 14.2m-tall structure stands in the natural landscape. (Roland Halbe)
A designed self-shaping process is a new approach to digital fabrication at the scale of building components. Rather than outputting machine codes to communicate a position for additive or subtractive shaping, the selfshaping process means geometry is communicated through the specific characteristic and arrangement of material, providing an implicit understanding of the resulting physical transformation.
As the scale of parts increase, the self-shaping processes become inherently more valuable as the force and coordination required to bend the parts increase. Similarly, self-shaping enables adaptable and parallel manufacturing within a standard setup, which is valuable for large quantity and high variation production.
Rethinking materials’ active role in construction leads to new architectural opportunities as well as increased sustainability in the production and operation of buildings. As our understanding and control of materials become increasingly sophisticated, their symbiotic relationship with the digitally-controlled fabrication machines of the future is brought into question, productively inverting and blurring the relationship between material and machine. Perhaps in the future the materials will do the fabricating and the machines as we know them will rest.