Square3 Spaceframe: ( twoway small square outer grid over
twoway larger square 
inner grid) 
. 



click image to enlarge 
a) outer grid 
b) inner grid 
c) strut diagram 
. 
Fig. 262  Square3 spaceframe
[demonstration model built with
small triangles (ST) ]* 
* can also be built with LT, and IT 


The
openness of the large square grid pattern of the inner layer is apparent.


The unit
cell is inherently unstable against torsional movement. Like
Square2, the entire 
structure
lacks torsional stability since both the outer and inner square grids run
parallel 
to each another. Therefore its perimeter must be adequately
supported to resist twisting. 
The framework can be
stabilized with panels or skylights inserted in the square openings. 





Fig. 263  Square3 unit cell 


click image to enlarge 
M = 52 J = 20 


52 < 3 (20 )  6 
(demonstration model) 
unstable, need +2 M 





In terms
of structural efficiency, it is midway between the more dense Square2
design 
and the less
dense Square1 spaceframe. 





Fig. 264  Carport with 
Square3 roof 

(scale visualization model) 
click image to enlarge 


. 
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to Knowhere 

Page 146
 Building stability  Square3 spaceframe 

