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Penthouse protection

Assisted by a technical arm of Switzerland’s Holcim Ltd., researchers deployed digital design and placement methods for an ultra-thin, curved concrete roof prototype at the ETH Zürich Robotic Fabrication Lab. The late-2017 demonstration of sprayed concrete on cable-bound, fabric formwork ushers a commercial premier at NEST, a project on the Empa-Wawag campus in Dübendorf, Switzerland.

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Researchers tested the ultra-thin concrete concept with an eye to NEST, a project under way on the Empa-Wawag campus and characterized as “a dynamic, modular research and demonstration platform for advanced and innovative building technologies.” Rendering: Doug & Wolf
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PHOTOS: Naida Iljazovic (formwork, shotcrete) and Michael Lyrenmann (finished shell) for Block Research Group/ETH Zürich
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The prototype took shape at the ETH Zürich Robotic Fabrication Lab. With participation from Holcim Schweiz staff, the Block Researcher team pegged a concrete mix fluid enough to be sprayed and vibrated, yet sufficiently viscous to remain on the fabric.

The prototype structure displays hyberbolic paraboloid forms across 1,722 square feet of surface area over a 1,290-sq.-ft. space. The shell reaches nearly 25 feet high and averages 2-in. thick, with a thickness range of 1.2-in. (edges) to 4.75-in. (support surfaces). The self-supporting shell has an inner concrete layer bearing heating and cooling coils plus insulation; an exterior concrete layer completes a sandwich-style cross section.

Researchers used a net of steel cables stretched into a reusable scaffolding structure and supporting a polymer textile functioning as formwork. The cable net is designed to take on the desired shape under the weight of the wet mixes, owing to a calculation method developed by the Block Researcher Group and Swiss National Centre of Competence in Digital Fabrication collaborators. Their algorithms ensure that forces are distributed correctly between the individual steel cables and the roof precisely assumes the target geometry.

The shell is envisioned for HiLo, a NEST penthouse apartment unit for guest faculty. Leading the ETH Zürich prototype and NEST projects are Empa-Wawag Professors of Architecture Phililppe Block and Arno Schlüter, who seek to integrate the new lightweight concrete construction with intelligent and adaptive building systems.