From: joshua geller (dclxvi_at_best.com)
Date: 05/14/98
Date: Thu, 14 May 1998 11:05:04 -0700 (PDT) Message-Id: <199805141805.LAA26079@shell5.ba.best.com> From: joshua geller <dclxvi_at_best.com> Subject: [nick_at_ece.vill.edu: Re: Domes lighter once built than their component parts? (Need a reference)]
The Butterfly writes:
> Still looking for the actual reference, but here's some math from one guy
> on the GEODESIC list...
> Nick Pine <nick_at_ece.vill.edu> writes:
PS > >Does anyone remember the reference for how a dome weighs less
PS > >once it's build than its component parts, due to the lifting
PS > >force of the air mass inside it? I think it's probably mainly
PS > >for larger buildings, like the 450' one in Southern California.
> I don't recall reading that anywhere, but it makes sense. If the dome
> is airtight at the top and warmer and/or more humid than the outdoors,
> the air inside will have a bouyant force, like a hot air balloon.
notice the two caveats; the dome must be airtight. I will add that it
if it is transparent you will get a greenhouse effect and the air will
be hotter.
> 70 F moist air weighs 0.073 lb/ft^3, and 30 F moist air weighs 0.081, and
> a 450' hemisphere contains 47.7 million cubic feet of air, so a 70 F dome
> might weigh 47.7x10^6(0.081-0.073) = 360K pounds or 180 tons less on an
> average 30 F January day in Philadelphia.
there you have it: if your 450 foot dome can be built weighing less
than 180 tons, it will have some static lift. I would guess that the
dome in LA weighs several orders of magnitude more than this.
now perhaps you have some understanding of the scale of the problem.
best,
josh