The Cadenza concrete spiral staircase designed by ETH Zurich and ROK Architects in Dübendorf showcases a novel fabrication technique using 3D-printed formwork for lightweight, reusable construction. Installed in the STEP2 Unit of the NEST research building, the staircase consists of 16 prefabricated steps connected through dry joints, allowing easy disassembly and reuse. The structure minimizes concrete use and integrates a post-tensioning system with memory steel for stability. This innovation promotes sustainability and demonstrates the potential of digital design in architectural applications, supporting the facility’s mission of advancing experimental construction methods.
The spine-like Cadenza concrete spiral staircase, designed by ETH Zurich researchers in collaboration with ROK Architects, highlights material-saving and reversible construction techniques. The Cadenza staircase is the newest addition to the NEST building, a lab for experimental fabrication methods shared by ETH Zurich and other research institutes in Dübendorf, Switzerland. The Cadenza staircase was installed between floors in the building’s newest unit, STEP2, and consists of 16 identical prefabricated concrete steps arranged in a helical form.
All the steps were cast from a single 3D-printed mould, reducing waste from traditional single-use concrete formwork, and are secured using dry connections. This allows the steps to be disassembled and reused in other buildings rather than being demolished. The concrete usage was minimized, contributing to the staircase’s distinctive slender, skeletal-like appearance. Benjamin Dillenburger, head of ETH Zurich Digital Building Technologies, stated that the staircase exemplifies the benefits of digital tools in architecture and engineering, and is ready for use in individual building projects.
Dillenburger explained, “Customised concrete structures pose challenges for conventional formwork. Digital design-to-production frameworks using 3D-printed formwork provide significant benefits in architectural expression, structural performance, and material efficiency. The steps are just 20 millimeters thick and have been structurally optimized for significant weight reduction. Their production generates minimal waste, as a single 3D-printed formwork set is used for all the steps.” The moulds for the steps are 3D-printed using carbon fibre-reinforced PET plastic. While some engineers may consider 3D-printing the stairs directly from concrete, the researchers prefer printing the formwork for its advantages.
Research assistant Angela Yoo said, “A compact, reusable set of 3D-printed formwork can be repeatedly used to cast multiple steps. This enables the assembly of multiple flights of stairs with minimal digital fabrication, making it an ideal solution for scalable production of bespoke designs.” Yoo added that this method also allows the integration of steel reinforcement, which is usually difficult with direct 3D printing, as the bars interfere with the fabrication process. The Cadenza staircase was assembled off-site and lowered into the NEST building by crane. However, ETH Zurich notes that it can be assembled and installed without heavy machinery, even in tight spaces such as during retrofits. The individual steps are made from ultra-high-strength, steel fiber-reinforced concrete and weigh 45 kilograms—about 60% lighter than conventional concrete steps. Various designs can be created using the same computational workflow, developed in collaboration with Swiss firm ROK Architects. Assembly is made possible by two key components: interlocking connectors printed into each step, allowing them to attach to one another with precision, and a system of three steel alloy cables that run through channels in the steps along the staircase’s spine.
The system uses post-tensioning, with tension applied to the bars only after the steps are in place, through a brief application of heat via a generator. This process pulls the steps tightly toward the staircase’s center. “The prestressing is based on so-called ‘memory steel,’ which can generate strong forces through heating and cooling,” said ROK co-founder Michael Knauss. “Compared to conventional methods, this system saves space and is easy to use.” The tensioning system is fully disassemblable, allowing individual steps to be removed, contributing to circular construction. The concrete is also expected to have a long lifespan, which some argue offsets its high carbon emissions.
“In many ways, prefabricated concrete parts contribute to sustainability in construction,” said Klaus Einfalt, CEO of fabrication partner SW Umwelttechnik. “Their stability, longevity, and recyclability make them a key factor for a sustainable future in construction.” The NEST building, led by Swiss research institutions Empa and Eawag, was opened in 2016. It features three open platforms where modules like the STEP2 Unit can be temporarily installed and later dismantled once the research is complete. Previous projects at the facility include the HiRes Concrete Slab ceiling with 3D-printed ventilation ducts and a robotic construction method for timber structures.
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Address: STEP2 Unit, NEST Building, Ueberlandstrasse 129, 8600 Dübendorf, Switzerland
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