Perspective - Image: AGENCE TER
In this project, we are working as structural engineers for the landscape design firm TER in Paris. TER is a landscape architecture and architectural studio that operates globally (they have projects in Paris, Los Angeles, Shanghai, Hamburg, Barcelona, etc).
Their most notable projects can be seen on their website: http://agenceter.com.
The structure we analyzed is part of a public park project with various facilities in Porte Pouchet, located north of Paris. The structure is a concrete sculpture made up of folded sheets, visually resembling the paper origami technique. Between the two sheets, there is a slide and a network of cables and tensioned meshes, forming a playground for children.
It is a large-scale element (12 meters in height) that serves not only as a recreational feature but also as a reference point.
1. BASIC CONCEPTS OF LAMINAR STRUCTURES
Experimenting with Sheets
The shapes of structural sheets are very diverse, and each of them determines a specific resistance behavior. The key is to mobilize resistance either through a locking system such as an arch or catenary, or by folding that provides inertia to the element.
Let’s explore these concepts using a sheet of paper.
First, let’s make the sheet of paper act as a cantilever:
If we hold the sheet of paper by two points, it will deform due to bending at a section near the clamping point where our fingers apply pressure. In this case, as the self-weight loads are perpendicular to the surface, the sheet must resist bending within the plane of the sheet. The bending resistance of a flat sheet, characterized by inertia, is virtually null since its thickness is very small (its inertia is exactly one-twelfth of the width multiplied by the thickness cubed)
If we fold the sheet in half and hold it, we can observe that the sheet shows almost no deformation. In this case, the inertia of the section resisting bending is increased. The same is observed if the sheet is placed vertically. As we add folds, the inertia decreases. In practice, the aim is to have the edge that minimizes its size or the weight of the structure.
Secondly, we will make the sheet of paper work as an arch or as a catenary.
By blocking the movement of both ends, the sheet of paper resists its own weight and can also bear additional loads. This happens because a resistant arch is formed, and the paper is compressed within its plane. The function of the structure is primarily compression, not bending, as in the previous case.
If we hang the sheet by its ends, we will have a work in a tensioned sheet, which is much more suitable for the properties of the paper. The load it can bear is much higher because we do not have the instability phenomenon that occurs when the paper is compressed (buckling or denting).
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