Tri-3 spaceframe:  (three-way triangular outer grid over three-way hexagonal inner grid)

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The Tri-3 spaceframe is created by periodically removing groups of six struts from the

inner layer of the Tri-1 design.  This forms a honeycomb-like inner layer of edge-connected

hexagons.  Some diagonal struts are also removed.

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tri-3_spaceframe.jpg

tri-3_spaceframe.jpg

tri-3_spaceframe.jpg

click image to enlarge

a)  outer grid

b) inner grid

c) strut diagram

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Fig. 237 - Tri-3 spaceframe  [demonstration model constructed from small triangles (ST) ]

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As with the model of the Tri-1 unit cell shown previously, the depth of the Tri-3 model can

be varied by using right triangles (RT), large triangles (LT), or isosceles triangles (IT).

 

A stability analysis of the unit cell of the Tri-3 spaceframe indicates that it is inherently

unstable (Fig. 238 a)

tri-3_spaceframe.gif

tri-3_spaceframe.gif

tri-3_spaceframe.gif

a)   M = 27     J = 12

b)    M = 30    J = 12

c)    M = 30    J = 12

27 < 3 ( 12 ) - 6

30 = 3 ( 12 ) - 6

30 = 3 ( 12 ) - 6

unstable, need +3 M

stable

stable

click image to enlarge

Fig. 238 - Stability analysis of the Tri-3 spaceframe unit cell  (demonstration models)

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Theoretically, the cell can be stabilized by inserting three more bracing struts as shown in

either b) or c) above to create a hybrid structure.  Or rigid panels or skylights can be

inserted into the hexagonal openings of the inner layer to stabilize the structure by means

of plate action as shown in Fig. 239 following.  Either way, adequate perimeter support

must be provided to help stabilize the structure.

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tri-3_spaceframe.jpg

◄  Fig. 239 Tri-3 spaceframe

tollbooth.jpg

stabilized with skylights

 

Fig. 240 Toll booth with

Tri-3 spaceframe roof ►

(scale visualization model)

click images to enlarge

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Page 138 - Building stability - Tri-3 spaceframe

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