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Rib-stiffened funicular floor system

This research develops the structure for an unreinforced concrete floor consisting of a thin funicular vault stiffened by a series of spandrel walls on its extrados. The structural floor is completed with tension ties, which link the supports and absorb the horizontal thrusts of the funicular shell. A first version of this innovation is built in the NEST HiLo project, realised in 2021 on the Empa campus in Dübendorf, Switzerland.

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Traditional concrete floor slabs working in bending typically consist of a solid section of concrete reinforced with large amounts of steel. In contrast, the HiLo floors use a thin, doubly curved funicular shell with vertical stiffeners to transfer loads to the supports through compression forces only. The forces are accumulated in the corners, where their outward thrust is absorbed in post-tensioned ties.

Thus, by placing material only where it is structurally needed, following the flow of forces in compression and tension, and by keeping all materials separate, the HiLo floor system saves 70% of concrete and 90% of reinforcement steel compared to the standard reinforced concrete slab, and allows for easy recycling at end of life.

Furthermore, the funicular geometry of the floors results in low stresses in the structure allowing low-strength materials with a low carbon footprint to be used, and even high percentages of construction demolition waste instead of our scarce natural resources.

This research was featured in the Beyond Bending exhibition at the Venice Architecture Biennale 2016. 

In HiLo @ NEST, these principles are for the first time demonstrated in a real building, providing an outlook at a real, disruptive opportunity to the construction industry to dramatically reduce carbon emissions by simply replacing an unexpectedly wasteful component of the buildings all around us.

Publications

Ranaudo F., Van Mele T. and Block P.A low-carbon, funicular concrete floor system: design and engineering of the HiLo floor,Proceedings of IABSE Congress 2021,Ghent,2021.accepted for publication.
Block P., Van Mele T., Rippmann M., Ranaudo F., Calvo Barentin C. and Paulson N.Redefining Structural Art: Strategies, necessities and opportunities,The Structural Engineer,98(1): 66-72,2020 (January).
Liew A., López López D., Van Mele T. and Block P.Design, fabrication and testing of a prototype, thin-vaulted, unreinforced concrete floor,Engineering Structures,137: 323-335,2017.
Wu H., Liew A., Van Mele T. and Block P.Analysis and optimisation of a rib-stiffened vaulted floor for dynamic performance,Engineering Structures,213: 110577,2020.
Block P., Van Mele T., Rippmann M. and Paulson N.Beyond Bending - Reimagining Compression Shells,Edition DETAIL,Munich,2017 (October).
López López D., Veenendaal D., Akbarzadeh M. and Block P.Prototype of an ultra-thin, concrete vaulted floor system,Proceedings of the IASS-SLTE 2014 Symposium,Brasilia, Brazil,2014.
ETH ZurichDARCHITA

 

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