This structure, known as the ‘future tree’ combines state-of-the-art design techniques, material science, and robotic fabrication to create an eye-catching architectural object. demonstrating the latest research of gramazio kohler research at ETH zurich, the ‘future tree’ consists of a funnel-shaped, lightweight timber frame structure built by a robot, and a bespoke concrete column created using an ultra-thin 3D printed formwork. the entire design and fabrication were developed as inseparable and fully digital processes.
Completed by gramazio kohler research, ETH zurich, the structure is located in esslingen, switzerland and stretches over the courtyard of basler & hofmann — a swiss AEC consultancy company that is also the project’s client and partner. ‘The future tree’s stem is a reinforced concrete column, made using an ultra-thin formwork, 3D-printed by a robot, and filled with a custom developed fast-hardening concrete,’ explains the design team. ‘this novel fabrication process, known as ‘eggshell’, allows for the fabrication of non-standard, structurally optimized concrete structures, whilst being able to integrate standard reinforcement and minimize formwork waste. The eggshell process makes use of fused deposition modelling (FDM) 3D printing in order to achieve a wide design and fabrication space.’
Measuring 2.1 meters in height (6′11′′), the formwork was built in one piece using a large scale printing setup consisting of a six-axis robotic arm combined with a vertical linear axis. ‘fabrication data for the 3D printing process were directly generated from the parametric design model, which allowed for rapid iterations of physical prototypes,’ the team says. ‘a common challenge in large scale 3D printing is shrinkage of the printing material when cooling. in the future tree column this issue was addressed by applying a diamond-shaped micro-pattern on the formwork. this helped to reduce stresses due to shrinkage while printing, as well as stiffening the formwork.’
The column is a first example of thin, 3D printed formworks used in a construction context.‘typically, formworks for concrete are thick sheets of timber or steel, with a support structure to withstand the hydrostatic pressure exerted by the freshly cast concrete,’continues gramazio kohler research.‘however, in the eggshell process it is possible to use a formwork with a thickness of only 1.5 mm by employing a sophisticated casting method. this casting method, first developed within the project smart dynamic casting (SDC) at ETH zurich uses a combination of admixtures to carefully control the setting of the concrete. in this way pressure on the formwork is reduced to a minimum and an 8 kg formwork could be used to fabricate a column of 800 kg.’
The canopy is a reciprocal frame spanning over an area of 107 square meters (1,152 sqf) and made of 380 unique acetylated timber elements that are butt-jointed using screws. the structure rests on the concrete column and is additionally anchored to the building on two sides. ‘thanks to the specific arrangement of its elements, a reciprocal frame can achieve a much larger span than the size of the elements would otherwise allow,’ says the team. ‘here, motivated by the frame’s structural behavior, the honeycomb pattern gradually transforms between a hexagonal and a triangular in order to achieve varying levels of flexural rigidity in different areas of the frame. the increasingly triangular configuration in the cantilevering corner makes this area stiffer and locally minimizes structural deformations.’
In order to study many instances of the design, the entire geometry and evaluation of the structure was programmed (described with an algorithm), including an automated data exchange between the architect’s modelling software (rhino) and the engineer’s structural analysis application (sofistik, autodesk RSA). ‘the computational model also facilitated a concurrent design approach, allowing to solve and coordinate different levels of details (LODs) and disciplines at the same time,’ explains gramazio kohler research. ‘for example, geometry of the screws connecting the timber elements was developed in parallel to the overall design, so that both structural integrity, architectural design but also fabrication feasibility could be continuously assured.’
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