Rec3
spaceframe: (twoway smaller rectangular outer grid staggered
over larger 
rectangular inner grid) 
. 
Periodically eliminating some struts in the Rec2 spaceframe results in
the Rec3 design. It 
is
similar to Square3 except for its rectangular grids. 



click image to enlarge 
a) outer grid 
b) inner grid 
c) strut diagram 
. 
Fig. 269  Rec3 spaceframe
[ demonstration model built with RT
(red) and ST (blue) ]* 

* can
also be built with LT and IT to increase depth 
. 
The
instability of the Rec3 unit cell is apparent from Euler's equation for
stable polyhedra. 
The entire structure is
torsionally unstable. Thus adequate perimeter support is necessary. 
. 



◄ Fig. 270  Stability analysis 
of Rec3 unit cell 
RT (red), ST (blue) 
Fig. 271  3 story office
building 
M = 52 J = 20 
with glazed
Rec3 curtain wall ► 
52 < 3 ( 20 )  6 
(scale visualization models) 
unstable, needs + 2 M 
click image to enlarge 



The forgoing section has shown that the omnitriangulated 
geometry of the octet truss harbors a plethora of structural 
designs attesting to its inherent diversity, efficiency, stability. 

◄
Fig. 272 Band shell created from the intersection of 100, 110, 
and 111 slices of the octet truss
(i.e. Square2, Rec2, Tri1) 


These
previous planar spaceframe designs are stabilized by means of
triangulation (lattice 
action),
and/or rigid panels (plate action) combined with adequate perimeter
support. 
However,
just as you saw that beams and vertical trusses can benefit from arching
their 
structures, arching spaceframes can stabilize their structures also.
This allows them to 
span
greater distances more efficiently than their planar counterparts. 
. 
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to Knowhere 

Page 148
 Building stability  Rec3 spaceframe 

