Thursday, February 16, 2006

Octet Truss

Portland World Trade Center
(photo by K. Urner, Olympus Stylus 500)

I took a series of photos yesterday focusing on an architectural feature of one of our downtown buildings: a spaceframe known as the octet truss. The above photo shows 12 spokes emanating from a common hub, corresponding to 12 balls around a nuclear ball in the face centered cubic packing (FCC).

I incorporated these shots into my slide show for sixth graders at Winterhaven today, along with a slide borrowed from my OSCON 2005 talk featuring Alexander Graham Bell standing next to one of his "kites" -- likewise an octet truss.

The photo below shows the 12-spoke hub in Bell's construction kit.

Fuller called this lattice the isotropic vector matrix (all vectors are the same length) and related it to Avogadro's ideal gas model.

Of course gas molecules aren't static, but their average uniformity in a volume might be associated with the isotropic distribution of "spherics" i.e. the rhombic dodecahedral voronoi cells around each ball in the packing.

Related reading:
More Oregon Curriculum stuff, posted from concourse B, PDX airport.