Colony Wall loading.

victoriatangoman wrote:

> I think
> that the structural design of the habitat will have to be designed
> specifically for any extraordinary structures within the the
> habitat. The ground of the habitat will include dirt, small hollow
> hills, lakes, forests, rivers, etc. We can probably estimate the
> loading that they would place on the structure beneath them. For
> multistorey buildings, all of that weight will have to be designed
> for.

Well, don't forget atmospheric pressure. 15 pounds per square
inch is 10 tonnes per square meter before you start. Typical
weight of stone is about 6 tonnes per cubic meter. I'd expect
that you would want a factor of 2 safety factor on your wall
strength and then add on other 10 tonnes of building.

So the required strength might work out at 40 tonnes.

Buildings would probably need foundations to even out the load.

> I've even toyed with the idea, within a cylinder habitat, of having
> a building near each endcap, that has a ground floor on each of the
> three land panels and each of the three buildings rise to join in
> the center. The buildings would have variable gravity and join at a
> minimal-g recreation center. From there, further construction could
> progress along the zero-g axis. But as I've been considering this
> plan, I've turned a lot of attention to the load factors that all of
> that building mass would place on the ground footprint. My gut
> feeling is that if these building are designed from the outset, then
> the structural design of the habitat could be such as to spread the
> load of the building mass.

You've missed a trick. If the building goes to the axis, then
it should hang DOWN from the axis. Tensile structures are much
cheaper to build than compressive structures; and it avoids
putting any load on the rim at all.

> Just think how cool it would be to go up the elevator in one
> building, transfer in the zero-g lobby and go down the elevator in
> another building. That lobby, having three elevator orientations,
> people exiting at different angles. WOW. That would put the tourist
> potential of the Empire State Building to shame.

Yes, very cool.

> I fear that it will be impossible to willy-nilly put up muli-storey
> buildings in the habitats. Single family homes will probably be
> tolerable. Office buildings - probably not.

Actually I'm thinking that low gravity is a great place for
um, sleeping. Other things, and sleeping. Mainly sleeping, but
other things too. I mean, the other things are tiring. ;-)
Plus there's the view. So the low gravity would be hotels
and expensive residences.

> The habitat as the ultimate planned community. When you reach plan
> capacity, build a new habitat. No rezoning allowed. No increasing
> densities allowed. It's built the way it's designed.
>
> This whole issue of loading has led me to give a long hard look to
> concrete construction for the habitats. Concrete can take impressive
> compressive loads, but to directly addresss your question - I'm not
> sure at the moment how thick the "floor" would have to be.

Habitats have large tensile loads; very few compressive loads.

> My seat of the pants approach for the moment is to work with the
> following assumption. Six feet of concrete for the outer shell.

I'm not sure. Probably have an outer rim of steel or aluminum,
then put a layer of rocks, then soil. The concrete is dead
weight because the rim is under tension from air pressure
mainly, plus any weight on top from soil and buildings.

Corrosion would be an issue. Probably double walling the
habitat with an outer walkspace would be a good idea then the
inner rim can be inspected and repaired.

--
- Ian Woollard (ian.woollard@...)

"Is a planetary surface the right place for an expanding
technological civilization?"
- Gerard O'Neill