Is there a limit to the height of a building?

Chris Smith put this question to engineer Allan McRobie...

Allan - I don’t really think there is a maximum height. We’ve already gone almost a kilometre Burj Khalifa. There are lots of proposals…

Chris - Where’s that one?

Allan - The Burj Khalifa is in Dubai. It’s a skyscraper; it’s almost a kilometre tall - 820 metres I think. But the trick to go higher is just to taper like the Eiffel Tower, like the Shard, like the Burj Khalifa is tapered. We’re having a bigger area at the bottom and you can spread the stress out more, so the pyramids are a nice example. You can just sort of keep going and make something the height of Mount Everest, or higher.

Chris - It’s amazing they realised that 5,000 years ago and it’s taken us all that time, in the meantime, to rediscover that.

艾伦-也许the other ones fell down.

Chris - I suppose so. Why should having a big base make a difference then? Why is that the way to go?

Allan - It just spreads out the load more so you get smaller pressure, smaller stress, so you can have an average stress all the way up.

Chris - What about the materials basis of this because concrete is wonderful but is it up to the job of continuously taking a load which gets higher and higher and higher? Because the bigger you’re building is the more load the ground at the bottom has got to take, hasn’t it?

艾伦,是的,没有。如果你尽快you are adding materials you can keep the stress the same. It works with any material whether it’s concrete, or ice, or marshmallow.

Chris - Sophie?

Sophie - If we’re going to eventually become an environmental constraint in terms of the height of the building - will it get too cold?

Allan - There are lots of constraints like that - the wind and so forth. I think there was a proposal a hundred years ago about a space elevator which was actually to build something all the way into outer space. The proposal’s still going; they're going to do it differently but the original proposal was to build it from from the earth all the way up to a geostationary orbit.

Chris - Were you also referring, Sophie, to the fact that in some countries people are demonstrating that you get significant changes in temperature in the local environment because of the built environment? You get buildings that radiate heat, they absorb heat during the day, they radiate that down at the ground. They also change the way the wind currents flow and this has a local effect on the environment which is not altogether great sometimes.

Allan - I completely agree. Euston Station forecourt for example; the buildings around it you get these local wind effects. You are exactly right there are lots of other things. Can you pour concrete; how do you get your concrete up there? There’s lots of other problems but the basic material problem is there’s basically there’s no limit to how high you can go.