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 Originally Posted by kingnat
I'd love to see a back-of-the-envelope-type calculation for this: http://www.viralnova.com/backyard-igloo/ that gives me reasonable confidence that something this size, with blocks this small has a very low chance of failure.
A dome is an incredibly stable structure, allowing for a lot of tolerance in deviation from the ideal shape.
Consider a hemi-spherical soap bubble on the surface of the dish water. A bubble is perfectly stable under the load of it's thin shell up to a certain size. Comparing the diameter of a large soap bubble to thickness of the bubble's shell is a pretty large number.
Since there's no pressure loading on the igloo shell, it all comes down to supporting its own weight, which it would do, even if it was much thinner than the 4 inches it looks to be.
So it comes down to loading. It's a practical aerodynamic shape, adjacent to the ground. My guess is that it would stand up to extreme winds in excess of 100 mph. Perhaps twice as high.
Additionally... I think a lake only needs to be frozen 6" thick to play hockey on it. This link seems to confirm that notion. According to this, at 4 inches of ice, a frozen lake is thick enough to ice fish.
If 4 inches with a transverse load of a human is safe enough to encourage the public to walk out on to it, then a 4 inch thick igloo that is adequately mortared should be able to support a person standing and maybe even jumping on it... maybe not even a thin person.
The snow-crete is a very nice mortar for this structure. If it's done right, it has just enough moisture to make a material bond with the ice blocks it's holding in place. Even if it's a little weak, you can add water and more snow in the joints and shore it up. It's a very strong structure because you're effectively welding the ice blocks together.
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I can break out some calculations for thin shell structures, but they're in the context of pressure vessels, and so the loading isn't the same. Nonetheless, thin hemispherical shells are amazingly efficient structures when pressure loaded. An inverted, weighted caternary (a la the St Louis Gateway Arch) is designed to have equal stress in all sections. If you built the igloo in this manner, you could make one the size of a large house, I'd wager. It's not like ice is weak in compression.
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