Fabrication and Construction - Tensile Fabric Structures: Design, Analysis, and Construction - page 139

subsequently, joined together. The patterns may be developed, for example, from the
three-dimensional “strips” by a “lay down” process which is described approximately
as follows:
1. Take the structure shown in 3D in Figure 9.1 and in plan in Figure 9.2. The
“strip” chosen here to serve as an example is heavily outlined on the figure.
2. Figure 9.3 shows this “strip” enlarged, isolated from the rest of the structure,
and with nodes labeled. At this stage the “strip” is still described in three-
dimensional terms and is not a pattern from which fabrication can be done.
3. Referring to Figure 9.3 since any three points define a plane, triangle 107-
108-124 defines a plane, or a flat surface. For convenience let this plane
represent a horizontal surface, such as a piece of fabric roll goods lying on a
cutting table, a datum plane, as it were.
4. Line 107-124, which is part of triangle 107-108-124 and which lies in the
datum plane, can be taken as a hinge, allowing node #108 to be lowered to the
datum plane. At this stage, triangles 107-108-124 and 107-123-124 both lie in
the datum plane.
5. Line 108-124, which is part of triangle 108-124-125 and which lies in the
datum plane, can be taken as a hinge, allowing node #125 to be lowered to the
datum plane. At this stage, triangles 107-108-124, 108-124-125, and 107-123-
124 all lie in the datum plane.
6. Continue this process of laying down succeeding triangles within the “strip”
until all triangles have been translated into the datum plane.
7. The resulting two-dimensional pattern is shown in Figure 9.4.
A fabric panel cut from this two-dimensional pattern, when joined to the other such
“strips” which constitute the entire fabric structure surface as shown in Figure 9.2,
will approximate the desired equilibrium shape of the tension structure. It should be
emphasized, that, at best, the resulting fabric assembly is only an approximation of
the original mathematical model of the structure. While individual fabric panels will
lie flat on the floor or ground, the assemblage of panels will not.
The amount of fabric pre-stress is determined by the designer. Often, however, this
decision is made with assistance from the fabricator and the material supplier. In
general, the pre-stress level should be set no higher than the minimum amount
necessary to stabilize the fabric, pull out wrinkles, and to keep the fabric from going