If you’ve ever held a folded piece of paper, you’ll have realised that the properties (namely stiffness) of the material are drastically different to the flat ‘stock’ sheet. This can be thought of as a ‘meta’ property of the paper.
Metamaterial properties are not born of the crystal structure of the metal, or the grain of the timber, but instead are properties of the geometry and distribution of material. Stiffness or controlled flexibility, control of failure, shear or bending strength and so on. This terminology is applied usually at a very small scale but we can co-opt the idea to demonstrate how foldability or crease patterns can be thought of as a meta-property.
We already manipulate properties in the design of structural sections, but an I-section, or H-section isn’t always the best for say, torsion. So we also have hollow sections – circular and others.
This is basic geometric manipulation of a section. On a larger scale, we manipulate schemes to better suit structural layouts for efficiency, but moving in the other direction – down to a smaller level we can use carefully planned folding to create geometric mechanical advantage for structural members.
Naturally, if you’ve ever worked with composite construction, you’re likely well aware of the folded sheet metal deck that forms the tension flange of a slab. These span a certain distance depending on the depth and thickness of the sheet.
From big to small
If we were to carefully design elements to be folded on-site in a controlled manner, we could transport bulk sheet materials in the form of timber panels with designed hinges, or sheet steel with thinned section in areas where we wish to bend them.
When loaded, a sheet of steel would then fold into a pre-determined ‘service geometry’ in the same way a precambered beam controls deflections.
The advantage to this is that the axial loading of a sheet would cause out of plane bending, and designed carefully can serve to strengthen such a structural element against the design loads.