Square-1 spaceframe: (two-way small square outer grid rotated 45^o relative to two-way

                                     large square inner grid)

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The struts of the inner grid are 1.414 times longer than the struts of the outer grid.

The unit cell is inherently unstable.  The lattice can be stabilized by adding extra bracing

struts to its perimeter cells as shown in Fig. 258 b) above (orange).  Panels or skylights

inserted into the square openings will further stabilize the structure. Also, sufficient support

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The Square-1 design is more efficient than Square-2 because it has one-half the number of

diagonal struts and fewer, longer struts in its inner grid.  This is an advantage for long

spans since the inner struts experience tensile stresses primarily.  Thus their slenderness

ratio is not a concern.  Also the diagonal arrangement of the inner grid relative to the outer

grid gives it increased torsional stability compared to the Square-2 design.  As a result the

Square-1 design uses about 80 % of the material used in Square-2 for a given span.

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