Gramazio Kohler Research

The project RIBB3D challenges the conventional design of floor slabs and allows to produce material-efficient reinforced concrete structures in an efficient manner. By using robotic 3D printing to create customised plastic formwork for a non-standard ribbed floor slab, the new approach offers 40 percent lower carbon footprint compared to conventional slabs using the same concrete mix, with no compromise on performance. Emissions can be further reduced with low-carbon concrete.
Reinforced concrete floor slabs typically account for more than half of the C02 footprint of a multi-storey building. Most often, concrete floor slabs are built as solid slabs, not because of their structural efficiency, but rather because of the efficiency of the planar formwork needed to cast them. The new RIBB3D solution succeeds in overcoming these limitations and uses digital fabrication processes to produce non-standard, optimised geometries.

Design and fabrication informed by flow of forces
RIBB3D combines structural engineering with digital fabrication tools to develop a workflow to design ribbed floor slabs based on the alignment of floor ribs along the direction of the bending moments. First, the researchers calculated the directions of the principal bending moments using finite element analysis (FEA) software. Thereafter, they imported the resulting vectors into a parametric design software, where the rib layout was generated. Based on the parametric model, the researchers performed structural analysis and ran optimisations loops to minimise material consumption.
This workflow was then used to design a multi-bay slab supported by columns on a grid of 8 x 8 meters, of which a section measuring 2.7 x 2.7 meters was fabricated. An industrial robot with a thermoplastic pellet extruder 3D-printed the formwork of the full-scale slab prototype. The structure was reinforced with conventional steel reinforcing bars and cast with standard self-compacting concrete.

Less material, same performance
The interdisciplinary research team used widely available technologies for concrete and reinforcement in combination with a novel concept for formwork to ensure compliance with building code regulations. The structural safety test of the full-scale section of the slab revealed that the optimised design could prevent brittle punching failures, and that the column-slab connection reached a capacity 80 percent higher than in a reference solid slab.
The results show that an optimised 2-way ribbed slab topology reduces the use of concrete by around 40 percent with respect to a conventional solid slab, while maintaining the same standards of structural safety, robustness and comfort, using conventional concrete. Combined with low-carbon concrete, the carbon footprint can thus be reduced by roughly two thirds. This highlights the potential of using 3D printed formwork to produce material-efficient floor slabs in an automated process, paving the way towards sustainable concrete construction.

Eggshell

Publications:

Burger J, Huber T, Lloret-Fritschi E, Mata-Falcón J, Gramazio F, Kohler M (2022). Design and Fabrication of Optimised Ribbed Concrete Floor Slabs Using Large Scale 3D Printed Formwork. Automation in Construction 144: 104599 PDF

Credits:

Concrete Structures and Bridge Design, ETH Zurich
Prof. Walter Kaufmann
Tobias Huber
Jaime Mata-Falcón

Gramazio Kohler Research, ETH Zurich
Prof. Fabio Gramazio
Prof. Matthias Kohler
Joris Burger
Ena Lloret-Fritschi
Ping-Hsun Tsai

Support: Structural Lab, ETH Zurich; Robotic Fabrication Laboratory, ETH Zurich; Concrete Lab, ETH Zurich

Sponsors: SACAC AG, Debrunner Acifer Bewehrungen

Funding: ETH Foundation, Siemens, Geberit, NCCR Digital Fabrication.


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