Prestressing: Dodecahedral cage made rigid via prestressed wires

Posted: May 23rd, 2010 | Author: John Zerning | Filed under: Prestressing | Tags: dodecahedron, Prestressing | No Comments »

Once again, curiosity and the pleasure of finding and working things out motivated this DIY project.

Being a keen cyclist, I am fascinated by the lightweight efficiency of the bicycle wheel with tension spokes. This small and inexpensive project is about applying the structural principle of the bicycle wheel to a spatial closed system.

The starting point were the two polyhedra: the great stellated dodecahedron inscribed in a dodecahedron. For the dodecahedral cage I used Herringbone struts (manufactured by Simpson Strong-Tie) and for the great stellated dodecahedron I used galvanised wires.

Instead of the turnbuckles I used long eye bolts with two nuts. To fix the wire end to the eye bolt I threaded the wire through the eye and bent it over by 180 degrees, then pushed a washer over the two wires and bent the end again.

I began by assembling the dodecahedral cage (the ends of the struts had prepared holes). As the form had “hinged” joints and no triangulation it collapsed! To make it stand up I temporarily stabilised all the 12 pentagonal faces with thin wires (radiating from the centre to each of the five vertices).

Next, piece by piece, the 90 prepared wires, with L-shaped ends, were fixed into their correct positions.

Finally, the exciting bit could begin – prestressing the structure one vertex at a time. With each complete cycle the structure became progressively stronger and stiffer – magic. Indeed, prestressed wires resist forces like columns! The larger the structure the more efficient it becomes.

Yes, I do, and I understand!

This is a good model of the synergy between the opposing forces (tension and compression).
The working together of the two forces to produce an effect greater than the sum of their individual parts.

The constant interaction between two opposing balancing forces in this closed system can stand as a metaphor for Yin and Yang!