Where Structure and Ornamentation Merge
Just 20 mm thick at its thinnest point, decoratively ribbed and not even half as heavy as a conventional concrete ceiling: with “Smart Slab”, the name says it all. The slab combines the structural strength of concrete with the design freedom of 3D printing. Developed by the research group of Benjamin Dillenburger, assistant professor for Digital Building Technologies at ETH Zurich, Smart Slab is one of the core elements of the residential unit DFAB House (see box) at Empa’s and Eawag’s research and innovation platform NEST in Dübendorf. The 80 m2, 15 t, ceiling consists of 11 concrete segments and connects the lower floor with the 2-story timber volume above.
Only as Much Concrete as Needed
Formwork production is the most labor-intensive step in concrete construction, particularly for non-standardized components. Since concrete is relatively cheap and readily abundant, the temptation is for the construction industry to produce the same solid ceilings over and over again, but the disadvantage is excessive material consumption and implicitly, a big carbon footprint. Digital fabrication methods can make a key contribution here: components can be optimized, enabling the necessary stability with far less material. The geometric complexity of a component does not matter in 3D printing, nor does it cause any additional costs – the printer simply prints what it is told to.
Computational Design Coordinates Parameters
“We didn’t draw the slab; we programmed it,” says Mania Aghaei Meibodi, Smart Slab project lead and senior researcher in Dillenburger’s group. “It would not have been possible to coordinate all these aspects with analogue planning, particularly with such precision.”
If you look at the ceiling from below, you see an organic ornamental structure with different hierarchies. The main ribs carry the loads, while the smaller filigree ribs are mainly used for architectural expression and acoustics. Statics and ornamentation go hand-in-hand.The lighting and sprinkler systems are also integrated into the slab structure. Their size and position were similarly coordinated with the planning software. In this way, the building technology disappears elegantly into the slab to occupy very little space. This saves only a few centimeters in the DFAB House project, but in high-rises this may mean a few extra floors could be fitted into the same height.
Fabrication at the Push of a Button
The 2 types of formwork for the concreting were then brought together by a third company, which first sprayed the fibre-reinforced concrete onto the sand formwork to produce the finely ribbed surface of the lower concrete shell and then casted the remaining concrete into the timber formwork.
Strong Thanks to Prestressing
Workers pulled steel cables lengthwise and crosswise through the concrete support and into the channels already inserted in the formwork. Tensioning the cables massively increases the system’s load capacity.
“It was spectacular to see on the construction site how seamlessly our elements fitted with each other and with the existing components of the DFAB House,” says Benjamin Dillenburger. “We owe this in part to the outstanding interdisciplinary collaboration with our partners. The meticulous work that we had invested into planning completely paid off.”
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