A Practical Guide to Tensegrity Design

Table of Contents

4 Higher-Frequency Spheres

Chapter 5

Double-Layer Tensegrities

5.1 Double-Layer Tensegrities: Introduction

For most of the tensegrities discussed so far, the tensile members
compose a single continuous spherical
layer.^{1}
Such structures are resilient, but are not very rigid and tend to
vibrate too much for many practical applications. Also, it seems
likely that large-frequency realizations of these structures, as
can happen with geodesic domes, have little resistance to
concentrated loads, so that it would be difficult to suspend
substructures from the their roofs, and they might cave in
excessively under an uneven load like snow.

These considerations
are a strong motivation for the development of a space truss
configuration for tensegrity structures. Such a configuration
would be analogous to the space truss arrangements developed for
the geodesic dome, like the Kaiser domes of
Don Richter,^{2}
or Fuller and Sadao's Expo '67
Dome,^{3}
and serve the same purpose.
Tensegrity space trusses are characterized by an outer
**and** inner shell of tendons interconnected by a collection
of struts and tendons. The result is a more rigid structure which is
more resistant to concentrated loads.

Designs for tensegrity trusses have been developed
in a planar context by several authors. The trusses
described in this book, especially the geodesic one described
in Section 5.3, are akin to those experimented
with by Kenneth Snelson in the
1950's.^{4}
Appendix A compares the truss of
Section 5.3
with an example from Snelson's work and another similar approach
from other authors.

In Section 5.2, a general approach to the design of tensegrity trusses is outlined. Then, in Sections 5.3 and 5.4, two examples are given of geometries which implement this approach. The second example demonstrates incidentally how icosahedral symmetries can be handled within the Cartesian framework.

^{1}
The only exception is the t-prism of
Section 2.2
which has a more cylindrical shape.

^{2}
*Fuller73*, pp. 62-63, 224-227.

^{3}
*Kenner76*, p. 115.

^{4}
See photos in *Lalvani96*,
p. 48.