Could I construct a dome to cover a whole city?

Engineer Hugh Hunt answered Heather's question... Hugh - Domes made of masonry, the kind of ones that the Romans built never got much bigger than about 30 metres diameter if we're lucky, modern domes, 300 metres diameter. I think the largest in the world is in Singapore, 330 metres diameter. So, to get to covering a city, my guess is that it would have to be quite a small city. 300 metres is not very far, but I think the biggest thing you have to remember is that it's not so much the forces required to make a dome that holds up its own weight. It's all the extra forces like weather, wind, snow. Even my cat Charlie, if it runs over the top of a dome, if the domes a really big, lightweight dome, that cat suddenly becomes really heavy. The other thing is that when the dome is half built, what happens if there's a big storm then?

Kat - Yeah, you can't just kind of drop it on top.

Hugh - So, you've got to think about how you build something.

Kat - Where would the key kind of stresses be? Would it collapse in from the top, in the middle, if you did manage to get it built?

Hugh - Well, that's an interesting question. If you think about a rugby scrum, that's a bit like a dome and how does that collapse?

Kat - Dome made of big men.

Chris - What about chickens and eggs because they have obviously come up with a way of making something which is extraordinarily strong in one dimension admittedly which is pole to pole? Georgia our producer made me stand on a box of eggs as an 'eggs-speriment' for Easter earlier this year. It did take my weight. There must therefore be a strategy that the chickens use to stop their eggs imploding on themselves. Can we do something similar?

Kat - Well chickens are a lot smaller than a city, Chris.

Hugh - That's it. It's quite a small structure. It's quite a small structure. It's made in really very well-controlled circumstances. So, when it then has to deal with the main forces of being an egg in the nest, it's pretty perfect. You probably don't want your dome to collapse on your city so that the.

Kat - It's risky, isn't it? It's a risky strategy so it's not looking like this is a good idea for Heather's novel, I don't think.

Hugh - Well, it's not bad if it's a small city.

Kat - So, it needs to be a small city made of really good engineers.

Hugh - And of course, if you're trying to make a big dome or a sports stadium, one thing is you're not allowed to have a pillar in the middle. That kind of spoils the game a bit. Now, these big domes for sports stadiums, the criterion is no pillars. But if you were going to do it for a city, maybe you don't mind having pillars. In which case, it then becomes a matter of, "Okay, how big do you want it?"

Kat - So, it's just like a marquee basically. So, I think there's your answer Heather. You can't have a dome, but you could probably have a really big marquee.