Towers and
space trusses |
. |
Non-space enclosing structures such as towers, antennas, and scaffolds can
also be |
triangulated for strength and stability. Another one of the first
structural uses for the octet |
truss
geometry was a twenty-five meter tall observation tower built in Nova
Scotia by Dr. |
Bell in
1907. Notice that the top of the tower is an octet truss that is
sliced parallel to the |
111
plane to form the viewing platform. The legs are sliced from the
octet truss parallel to |
the
squared 100 plane. |
. |
 |
|
 |
◄ Fig. 297 - Bell's
tower (1907) |
|
scale visualization model ► |
(built with all LT) |
|
click image to enlarge |
|
|
. |
Other
freestanding tower designs can incorporate elements of the octet truss.
Fig. 298 |
shows
two tower designs based on the octahedron. Fig. 298 a) is a lattice tower, called |
Type A,
comprised of octahedral cells joined face to face. Readers of
the previous lesson |
. |
 |
|
 |
|
Fig. 298 - Type A and B |
Fig. 299 - Type B |
towers |
unit cell |
|
M = 20 J = 9 |
(demonstration models) |
20 < 3 ( 9 ) - 6 |
click image to enlarge |
unstable, needs +1 M |
|
ST (blue), RT (green) |
|
|
|
. |
on
crystallography will recognize it as being structurally identical to a
section of the HCP |
crystal
lattice structure (a variation of the octet truss). Since the tower
is completely |
triangulated, it is inherently stable. Fig. 298 b) shows a tower, Called type B, built from |
octahedra that are joined vertex to vertex. Vertical braces, or
stays (green), are used to |
position
the octahedra upright. The unit cell of this structure, pictured in
Fig. 299, is not |
stable.
Therefore it must be braced against torsional or twisting movement.
This can be |
done,
redundantly, by cross bracing the face of the rectangular shaped sections
with cable. |
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to Knowhere |
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Page 155
- Building stability - Towers and space trusses |
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