ETH Zurich has fabricated the world's tallest 3D-printed structure. With the construction of the White Tower in Mulegns, researchers hope to bring innovative technologies to commercial maturity.
Motes of dust hang suspended in the cool air of the Robotic Fabrication Laboratory (RFL). Researcher Che Wei Lin carefully checks the alignment of a yellow formwork panel before giving group leader Ana Anton a thumbs-up. Control unit in hand, she fires up the 3D printer. It clatters into life, pumping smooth white concrete through a nozzle attached to a robotic arm. Whirring softly, the robot evenly extrudes the first layer directly onto the formwork panel, tracing an ornate pattern of two intersecting circles, each with a crenellated inner lining. Following a media event to mark the official start of operations, this is the first regular day of production for what is to be the world's tallest 3D-printed building.
Known as Tor Alva ("White Tower"), this structure has been designed by Benjamin Dillenburger, ETH Professor for Digital Building Technologies, and architect Michael Hansmeyer, working in collaboration with ETH professors Robert J. Flatt and Walter Kaufmann. It is clear, even to the untrained eye, that this is no ordinary piece of architecture. Crafted from gleaming white concrete, its sculptural columns are branched and elaborately textured. Ascending over four storeys, the structure becomes increasingly ethereal, the columns taller, more slender, until they bifurcate once again to create a domed space that crowns the tower. The structural challenges posed by this complex design were formidable. Yet with the help of Swiss engineering firm Conzett Bronzini Partner, a team of ETH researchers - Timothy Wangler, Alejandro Giraldo Soto, Lukas Gebhard and Ana Anton - proved more than equal to the task.
Far from the bustling streets of Zurich, Tor Alva will stand in Mulegns, an isolated village on the Julier Pass in the canton of Graubünden. The idea is that this unique structure - along with a lively arts programme for the tower's dome - will draw tourists to Mulegns and breathe new life into the village, which has been struggling to survive. Once upon a time, skilful artisans from this part of Switzerland - confectioners, master builders, stucco plasterers - exported their expertise around the globe. They brought back wealth to the Alpine villages, building schools and fine houses. Yet the era of prosperity is long gone. Today, fewer than 20 people live in Mulegns. Happily, the Origen Foundation (Nova Fundaziun Origen) has refused to abandon the village to its fate, joining forces with ETH Zurich to create a striking memorial to the artisanal skills for which this Graubünden village was once renowned: a spectacular tower, built with the latest digital construction technology and providing a space for art, music and theatre.
New design language
After just one hour of printing, the column element has grown by 1 metre. It is now clear why the White Tower is perfect for Mulegns: the eight-millimetre-thick extrusions look just like fondant icing piped from a confectioner's bag. At regular intervals, the nozzle at the end of the robotic arm deviates ever so slightly from its circular path. The liquid concrete oozes over the edge of the growing column and hardens to create a small, droplet-like relief. Once a number of layers have been completed, one can see that these droplets form a spiral pattern on the column surface. "The fluidity of the extruded material gives us decorative options," Hansmeyer explains. The droplet motif is set in high relief above the thin strata formed by the extruded layers, giving the column a rich textural depth - simple yet luxuriant, as though created by nature itself. The novelty of the design stems from an underlying algorithm that can generate a host of shapes in different variations. For the robot, it makes no difference: complex curves are just as easy to create as straight lines. For the architect, as Hansmeyer explains, it provides a totally new design language - as well as an efficient and cost-effective way of producing customised and one-off components.
"Digital handicraft" is how Dillenburger and Hansmeyer describe this architecture. Unlike conventional concrete casting, the additive manufacturing process does not require the use of formwork and therefore enables a virtually limitless choice of surface pattern. That said, this requires precise control of not only the robot's movements but also the properties of the material being extruded. In this case, the concrete must be soft and workable enough to form the desired motif yet harden quickly enough to bear the succeeding layers. Robert Flatt, ETH Professor for Physical Chemistry of Building Materials, has devised a new concrete mix for Tor Alva that reconciles these conflicting demands. Just before the concrete leaves the pressurised nozzle, two additives are blended into the mix to facilitate formation of the droplet-shaped motif.
Rebar by robot
Simple one- or two-storey houses produced by additive manufacture are nothing new. What's special about Tor Alva is that the 3D-printed elements are load-bearing. This breakthrough was achieved through collaboration between Dillenburger's research group and ETH professors Kaufmann and Flatt - together with the ETH spin-off Mesh and construction company Zindel United. During the fabrication process, a second robot inserts a ring-shaped steel reinforcement element into the growing column after each 26 centimetres of height. The addition of these rebars makes it possible to produce complex, branched columns that would be difficult to realise using a conventional concrete-casting process. "Quadruple branched columns like those in the domed stage of the Alva Tower are a rarity!" Lin explains.
Funded by the Escher Circle at the ETH Foundation, this project aims to push back the boundaries of additive manufacturing while exploring where 3D printing offers advantages over traditional methods. It also breaks new ground in structural engineering, since no tested norms exist for the reinforcement of load-bearing 3D-printed elements. Kaufmann, ETH Professor of Structural Engineering, and his team have developed a rebar concept and a test procedure that can accommodate the heterogeneous properties of the layered constructions produced in additive manufacture. In conjunction with stress tests on originally sized pillars, this will ensure the structural integrity of Tor Alva.
Mulegns, 30 September 2024
All eyes are turned aloft: suspended from four chains, a gleaming white column is hoisted up by crane. Against the rustic backdrop of Alpine meadows and wooden cowsheds, the flying sculpture looks like something from another world. It finally comes to rest atop the historic coach house. Situated at the heart of the village, this building is to serve as the entrance to the tower and will dovetail to create a structure somewhere between Alpine tradition and 21st century digital architecture. It is the fourth and final storey of the tower that is being delivered and erected today. Two dozen or so spectators - both locals and passers-by - have settled on the meadow opposite to take in the show.
It took 5 months to fabricate a total of 124 elements at ETH's Robotic Fabrication Laboratory. These two-metre-high sections were then joined together with vertical rebars to form finished columns at a warehouse in Savognin, further down the valley from Mulegns. The base and capital for the columns were cast in concrete, but using a new type of 3D-printed mould produced by ETH spin-off Saeki. These horizontal elements incorporate all the holes and fixtures required to join up the elements for the 30-metre-high tower. It's a painstaking business ensuring that everything lines up correctly. But it all goes surprisingly smoothly. In fact, it takes just one day to deliver the modules for a single storey, hoist them into position and bolt them together. "We're trialling a method of circular construction here," Dillenburger explains. Scheduled to stand for five years in Mulegns, the tower can later be dismantled and re-erected at another location.
Who dares wins
Dillenburger is not proposing that this technique will come to replace conventional housebuilding. But, in many cases, he suggests, 3D printing or other forms of automated construction could provide a more economical solution than traditional concrete casting. The extrusion process only applies concrete where it is actually needed, resulting in significant savings on the amount of material used. Similarly, the level of automation involved could provide an answer to the global shortage of skilled labour.
"Before a new innovation can gain a foothold in the construction industry, we need experience of how it works on a large scale and over a substantial period of time," explains research group leader Ana Anton. That's the value of audacious projects such as Tor Alva, which dare to explore the use of new technology in architecture and structural engineering. Due to open in May 2025, the White Tower will provide a spectacular showcase for digital architecture - just as the Graubünden confectioners and master builders once exported their skills to the rest of the world.
