Materials researchers from ETH Zurich has revealed a prototype for an ultra-thin, sinuous concrete roof system with an average thickness of just 5 centimeters. Using digital design and fabrication technologies, the team was able to calculate and construct a self-supporting shell structure using the minimal necessary material. This was facilitated through the use of a novel formwork system consisting of a net of steel cables and a polymer fabric stretched into a reusable scaffolding structure.
The prototype covers a floor area of 120 square meters with a 160-square-meter surface area. Structural analysis calculated the exact thickness of the material throughout the shell, with thickness varying between 3 centimeters along the edges of the roof to 12 centimeters at the crucial support surfaces.
The researchers, working under Block Research Group, believe that the unique steel-net formwork system developed for the project could quickly be adopted in the construction industry as it allows for reduced material cost and less invasive structuring – during the concreting of the roof, the area underneath remained unobstructed, allowing interior work to continue simultaneously.In a four-year-long research process, the team also developed a proprietary spraying technique that allows the concrete to be viscous enough to stick to the formwork while staying liquid enough to be sprayed through a nozzle.
This new formwork technology will be utilized for the first time in a real-world project in a planned roof-top residential unit called HiLo, built on top of the NEST living laboratory in Dübendorf, Switzerland. This project will integrate insulation and heating and cooling coils on top of the inner concrete layer, upon which a second layer of concrete will be sprayed. The upper surface will then be clad in thin-film photovoltaic cells to allow the residence to be energy-positive.
“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,” says Prof. Block, leader of Block Research Group. “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.”
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