On 2008-04-08 08:36:26 -0700, jdnicoll@[EMAIL PROTECTED]
(James Nicoll) said:
> In article <slrnfvm0d8.5me.tim@[EMAIL PROTECTED]
>,
> Tim Little <tim@[EMAIL PROTECTED]
> wrote:
>> On 2008-04-08, Charles Talleyrand <kitplane01@[EMAIL PROTECTED]
> wrote:
>>> I don't think one can build a dome over even a medium city with
>>> current technology.
>>
>> That depends upon what you mean by "dome". A structure sup****ted only
>> at its perimeter, almost certainly not. An enclosing roof with plenty
>> of internal sup****ts definitely could be done. It would be
>> ridiculously expensive and take ages to build.
>>
> What are the limits on domes held up by air?
I know nothing of such stuff but the first things I would start
worrying about are:
1. Stability. A wide low-pressure dome (where the air pressure
basically holds up the membrane, nothing more) will want to collapse in
one region and bulge up in another. (You could avoid this by having
enough pressure to keep the membrane under tension (how much tension is
enough?) but then you can't scale it up arbitrarily large. Dunno if you
could still cover a city with modern materials.) Maybe this could be
fixed by anchoring/guying the membrane at frequent intervals inside,
which could be done with cable instead of pillars and pylons so maybe
it'd be easier. It would be like living inside a quilt.
2. Air quality. Since the whole point of the dome is to prevent city
air from mixing with outside air, suddenly in-city air pollution
becomes a larger problem. No paper mills or internal-combustion
vehicles, I'm thinking.
3. Outside weather. Will wind flatten the dome against the buildings on
the inside (and crush them)? Worse, if he membrane isn't under enough
tension, it would probably flap in the wind and be shredded in short
order. Another point in favor of a high-pressure tensioned dome, I
guess.
4. Outside weather part 2: Rain and snow load on the dome. You can
crank up the air pressure to compensate, but it's probably a variable
and uneven load.
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