Octet Truss Screen

The archetypal element to shape space in the garden is the screen. Traditional screens are two-dimensional constructions. Three-dimensional screens require less material, enable sculpted shapes and a richer planting scheme. They also touch the ground very lightly with minimum disturbance to the soil. The modular units of an octet truss are alternating octahedra and tetrahedra, thus it is a truss with omnitriangulation, which results in a highly efficient space frame configuration. Generally octet trusses are constructed of struts all with equal length, in order to simplify construction.

However, with my simple universal joint the strut lengths can vary, allowing easy low tech fabrication. I do not see these minimal octet trusses as sculptures. Their job is to support, train and display plants and thus they become invisible, analogous to the skeletons in animals.

1. Building blocks – octahedron and tetrahedron – of the octet truss. This example has five different strut lengths.
2. Octet truss screen with a chamfered top edge.
3. Octet truss screen on an inclined ground.
4. Octet truss forming a curved screen.
5. Octet truss forming a curved screen.
6. Octet truss forming a screen with a right angle.

Building blocks - octahedron and tetrahedron - of the octet truss. This example has five different strut lengths.Octet truss screen with a chamfered top edge.

Octet truss screen with a chamfered top edge.

Octet truss screen on an inclined ground.

Octet truss forming a curved screen.

Octet truss forming a curved screen.

Octet truss forming a screen with a right angle.

Toroidal Pergola

A toroidal trellis on stilts gives climbing plants optimum growing conditions due to the hole in the middle, thus minimising shading from the leaves. Also, the open centre is like a clearing in the forest, permitting light to enter the ground.

So why are we not seeing toroidal trellises in our gardens?

1. Doughnut shaped space frame trellis formed by an octamast (assembly of octahedra) bent into a ring and supported on two octahedra. This toroidal pergola clothed with climbing roses will be a magnificent sight and also perfume the air.
2. Plan view.

Doughnut shaped space frame trellis formed by an octamast (assembly of octahedra) bent into a ring and supported on two octahedra. This toroidal pergola clothed with climbing roses will be a magnificent sight and also perfume the air.

Plan View.

Geodesic Gridshell Pergola

The flat “lattice” (beams and cross members) roofs supported on columns are the most common trellises in our gardens. They are heavy in every sense, materially and visually. Yes, they are easy to make/erect and inexpensive. And these are good reasons why they will continue to be ubiquitous.

However, occasionally we should aim a bit higher and design/build trellises that express contemporary ideas about the geometry of spatial forms. For me this means doing more with less.

The illustrations here show a gridshell pergola. Its surface is synclastic, i.e. having curvatures in the same sense (concave or convex) in all directions through any point. The geometry of this geodesic gridshell is generated by projecting (from the centre) the edges of a cube onto the circumsphere. It is 1/6th of the sphere’s surface. This surface is further subdivided forming a quadrangular mesh following great circle arcs.

Note, a geodesic gridshell lattice cannot be laid out flat, which gives the structure extra stiffness. Structural designs that follow nature’s example, i.e. geodesic principles, will result in obtaining minimal, highly efficient forms which are beautiful, in harmony and at ease with nature.

1. Sphere with a geodesic quadrangular pattern.
2. Geodesic gridshell supported on four tetrahedra.
3. Horizontal projection of the gridshell.
4. An aggregate of gridshells.

Sphere with a geodesic quadrangular pattern.

Geodesic gridshell supported on four tetrahedra.

Horizontal projection of the gridshell.

An aggregate of gridshells.

Postscript

Space frame trellis design and construction, which is essentially spatial model building on a bigger scale, is an excellent vehicle for structural explorations that can be applied to numerous structural design problems, on many different scales. For the structural maquettes I use paper straws and for the connectors short lengths (30mm) pipe cleaners. You can make a many-way joint (2, 3, 4, 5, 6, 7 etc).

For example, in case of a three-way joint you will need three short lengths of pipe cleaners.. Two go into each end of the straws, thus forming a universal joint.

Explorations in geometry based on the polyhedral approach are the stuff of creativity.
A famous Chinese proverb says:

I hear, I forget; I see, I remember; I do, and I understand.