Square1 spaceframe: (twoway small square outer grid rotated 45^{o}
relative to twoway 
large square inner grid) 
. 



click image to
enlarge 
a) outer grid 
b) inner grid 
c) side view 
. 
Fig. 258  Square1 spaceframe
(demonstration model constructed from ST
and RT) 

. 
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 
must be given to the perimeter for torsional stiffness. 
. 



M = 16 
J = 8 

16 < 3 ( 8 )  6 
unstable, need +2 M 
RT (blue), ST (yellow) 
(demonstration model) 
click image to enlarge 

Fig. 259  Strut diagram 
Fig. 260  Square1 unit cell 


. 
The
Square1 design is more efficient than Square2 because it has onehalf
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 Square2 design.
As a result the 
Square1
design uses about 80 % of the material used in Square2 for a given span. 
. 





Fig. 261  Square1 glazing 
framework for solarium 

(scale visualization model) 
click image to enlarge 


. 
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Page 145
 Building stability  Square1 spaceframe 

