Dome design

[Charles J Knight <c dot knight at juno dot com>]

The other day, I was reading a book on Middle Eastern architecture.  It 
mentioned that with the use of mud brick, domes could be quickly and 
easily built.

BUT it also mentioned that all barrel vaults and domes had to posess 
a parabolic shape, so that the forces involved would be purely 
compressional, since mud bricks can't tolerate *ANY* tensile forces.

Due to this, there is a unique and characteristic shape to all
traditional
buildings in the middle east, especially around Egypt.

A modern renaissance in mud-brick design, spearheaded by Hassan 
Fathy, started with his attempts to build spherical domes from mud 
brick -- they failed miserably.  Only when he changed to the local 
traditional shape, which happens to be parabolic, would his domes 
remain standing.

("An Architecture for People:  The Complete Works of Hassan Fathy")

Of course, I immediately started thinking about geodesic domes.  While 
a sphere is indeed the most efficient way to enclose space, period, is 
it the *best* way to enclose space in a gravity field?  Or would a
parabolic 
dome work even better in this application?

We all know that spherical geodesics resist outside forces, such 
as those encountered underwater, beautifully.  But those are not a 
unidirectional force, like gravity is...

We've heard about troubles with local buckling, etc, with high frequency
spherical domes...could this be the result of choosing an incorrect 
geometry -- one which isn't taking gravity into consideration?  Could it 
be that the hubs aren't holding the struts into place as effectively as
they
could?  (Bucky's main complaint about rectilinear homes was that the
corners held the struts rigidly into place, instead of using natural
geometry
to maintain the form)

Has anyone ever studied this aspect of dome design?

     -- Chuck Knight