Researchers from ETH Zurich have built a prototype of an ultra-thin, curved concrete roof using innovative digital design and fabrication methods. The tested novel formwork system will be used in an actual construction project for the first time next year.
A prototype for an ultra-thin, sinuous concrete roof using innovative design and fabrication methods has been designed and built by researchers from the ETH Zürich. The shell is part of a roof-top apartment unit called HiLo that is planned to be built next year on the NEST, the living lab building of Empa and Eawag in Dübendorf. The penthouse will provide living and work space for guest faculty of Empa. Researchers led by Philippe Block, Professor of Architecture and Structures, and Arno Schlüter, Professor of Architecture and Building Systems, want to put the new lightweight construction to the test and combine it with intelligent and adaptive building systems.
The self-supporting, doubly curved shell roof has multiple layers: the heating and cooling coils and the insulation are installed over the inner concrete layer. A second, exterior layer of the concrete sandwich structure encloses the roof, onto which thin-film photovoltaic cells are installed. Eventually, thanks to the technology and an adaptive solar façade, the residential unit is expected to generate more energy than it consumes.
Tried and tested to scale
The building technique for the roof was developed by the Block Research Group, led by Prof. Block and senior researcher Dr. Tom Van Mele, together with the architecture office supermanoeuvre, and tested out on a full-scale prototype. The prototype, which has already been dismantled to make space for future experiments, was 7.5 m high with a surface area of 160 m2 (covering an area in plan of 120 m2). The thickness of the concrete has an average thickness of 5 cm varying between 3 cm along the edges of the roof to 12 cm at the support surfaces.
Instead of formwork using non-reusable custom-fabricated timber or milled foam, which would be needed to realise such sophisticated form, the researchers used a net of steel cables stretched into a reusable scaffolding structure. This cable net supported a polymer textile that together functioned as the formwork for the concrete. This not only enabled the researchers to save a great deal on material for construction, they were also able to provide a solution to efficiently realise completely new kinds of design. Another advantage of the flexible formwork solution is that during the concreting of the roof, the area underneath remains unobstructed and thus interior building work can take place at the same time.
Algorithms for controlling the shape
The cable net is designed to take on the desired shape under the weight of the wet concrete, thanks to a calculation method developed by the Block Researcher Group and their collaborators in the Swiss National Centre of Competence (NCCR) in Digital Fabrication. The algorithms ensure that the forces are distributed correctly between the individual steel cables and the roof assumes the intended shape precisely. The cable net weighs just 500 kg and the textile 300 kg; thus, with a total of only 800 kg of material the 20 tons of wet concrete are supported.
The construction of the roof would be inconceivable without state-of-the-art computation and fabrication techniques, but the project also heavily relied on the expertise and experience of several craftspeople. Experts from Bürgin Creations and Marti sprayed the concrete using a method developed specifically for this purpose, ensuring that the textile could withstand the pressure at all times. Together with Holcim Schweiz, the scientists determined the correct concrete mix, which had to be fluid enough to be sprayed and vibrated yet viscous enough to not flow off the fabric shuttering, even in the vertical spots.
Proof that it works
Block’s team built the prototype over the course of six months in ETH Zurich’s Robotic Fabrication Lab. It represents a major milestone for the NEST HiLo project: “We’ve shown that it’s possible to build an exciting thin concrete shell structure using a lightweight, flexible formwork, thus demonstrating that complex concrete structures can be formed without wasting large amounts of material for their construction. Because we developed the system and built the prototype step by step with our partners from industry, we now know that our approach will work at the NEST construction site,” says Block.
The process to get to this point took almost four years, from the start of the project to the finished prototype, partly because Block wanted to involve several industry partners in development of the prototype. Next year, he plans to build the roof once again at the NEST building in eight to ten weeks. The individual components of the roof structure can be reused as often as needed. The cable net can be dismantled into a few parts that can be quickly reassembled and rehung.
Block Research Group:
Throughout history, master builders have discovered expressive forms through the constraints of economy, efficiency and elegance, not in spite of them. We have much to learn from their architectural and structural principles, their design and analysis methods, and their construction logics. Inspired by master builders and learning from the past, the BRG aims to provide appropriate assessment strategies for architectural heritage, develop novel structural design approaches for highly efficient and expressive structural form, and propose and implement new and economical construction paradigms.
Analysis of masonry structures
Much of our architectural, cultural and structural heritage consists of unreinforced masonry. These historic structures fail mostly due to instabilities caused by large deformations and displacements. The standard structural analysis tools used in engineering practice today are not well suited to deal with these types of structural problems, not in the least because of the unknowable material properties of historic masonry constructions. The BRG develops a robust computational basis for a fully three-dimensional method for limit analysis of vaulted masonry structures with complex geometry. In addition to computational methods, the BRG also studies masonry structures by means of scaled models. Collapse mechanisms can be simulated using an actuated testing table, an optical registration system, and 3D-printed scale models. Learn more.
Graphical analysis and design methods
The BRG develops structural design, form finding and analysis methods, such as three-dimensional graphic statics, that rely on geometrical rather than analytical or numerical representations of the relation between “form and forces” in a structural system. Such explicit approaches provide continuous, bi-directional control over both spatial and structural characteristics in a common visual language that is equally accessible to architects and engineers and therefore extremely useful during early shape and equilibrium explorations. Learn more.
Computational form finding and structural design
The BRG has developed a computational framework that contains several flexible data structures, novel and efficient solving algorithms, and numerous nonlinear optimization and solving procedures. This allows us to develop new (hybrid) solving strategies for equilibrium problems, often significantly improving solving times and robustness compared to existing approaches. Ultimately the computational methods developed have led to novel structural typologies and structural design approaches for highly efficient, expressive forms. They have enabled the extension of our expertise in compression-only problems to other structural systems, such as thin concrete shells, “bending-active” membrane structures, fabric formwork systems, and general spatial systems of forces with applications in bridge design and large-span roofs. Learn more.
Design of discrete assemblies
Discrete-element assemblies are structures formed by individual units. These range from structures consisting of relatively small units, such as historical masonry structures, to contemporary large-scale assemblies composed of prefabricated, multi-material building parts or entire building units. Favouring no-tension connections, this research extends and develops novel digital design and engineering approaches that address structurally informed discretization (digital stereotomy), stability during and after assembly, and structural optimization of discrete-element assemblies. Learn more.
Fabrication and construction technologies
The objective of this research is to develop and implement new, economical construction techniques for structural systems with complex geometries. We propose and instigate new paradigms for structurally informed, optimised building processes in architecture as well as innovative structural design strategies that utilise bespoke fabrication. We seek to define mechanisms to intelligently and efficiently include structural performance information explicitly into architectural geometry and digital fabrication algorithms. Imposing structurally informed constraints allows for more holistic design processes that do not detach formal design from limitations on cost, construction, longevity or structural properties of the chosen material systems.
Part of the National Centre of Competence in Research (NCCR) in Digital Fabrication, the BRG develops structurally informed, optimised building processes in structural design and innovative solutions in prefabrication. Learn more.
The BRG does not stop at developing new computational design strategies that generate expressive and efficient structural form, but also develops novel solutions to realize these complex shapes. This puts the BRG in the unique position to participate in real construction projects that showcase the innovative structures developed while also feeding valuable insights back into the academic research. Choosing projects in both high- and low-tech contexts further forces the adaptation of the developed methods and tools to varied social, cultural, and geographical conditions. Check out the Projects page to see some of our latest research being applied in exciting demonstrators or real constructions.
Innovation in Teaching
The BRG’s research on graphical methods is also applied in the teaching of architecture students at ETH Zurich. Structural design courses are team-taught together with the Chair of Structural Design Prof. Dr. Joseph Schwartz. This collaborative teaching effort, which began in 2015, is funded by an Innovedum grant and seeks to continue the legacy of former ETH educators including Karl Culmann, Karl Wilhelm Ritter, and Pierre Lardy. Particularly through the use of the interactive and dynamic learning and teaching platform eQUILIBRIUM, students gain an understanding of the relationship between the shape of a structure and the forces in it.
The goal of all BRG-produced tools and platforms including eQUILIBRIUM and RhinoVAULT is to “whiten the black box,” making the methods and their implementations explicit and intuitive to the user throughout the early stages of the design process.