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


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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