Rec-3 spaceframe:  (two-way smaller rectangular outer grid staggered over larger

                                rectangular inner grid)


Periodically eliminating some struts in the Rec-2 spaceframe results in the Rec-3 design.  It

is similar to Square-3 except for its rectangular grids.




click image to enlarge

a) outer grid

b) inner grid

c) strut diagram


Fig. 269 - Rec-3 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 Rec-3 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 Rec-3 unit cell

RT (red), ST (blue)

Fig. 271 - 3  story office building

M = 52    J = 20

with glazed Rec-3 curtain wall ►

52 < 3 ( 20 ) - 6

(scale visualization models)

unstable, needs + 2 M

click image to enlarge



The forgoing section has shown that the omni-triangulated

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. Square-2, Rec-2, Tri-1)


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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Page 148 - Building stability - Rec-3 spaceframe

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