• Question: Why don't spiral staircases collapse?

    Asked by mrsrichards to Andrew, Daniel, Hayley, Natalia, Peta on 17 Nov 2011.
    • Photo: Daniel Scully

      Daniel Scully answered on 15 Nov 2011:

      Because the step extends either into the outer wall or into the central post (depending on how they’re built).
      It’s the outer wall or central post which holds each step up.

      in fact even straight staircases are built this way – the steps are supported on either side. That’s why most houses have cupboards under the stairs – you don’t need anything underneath to hold them up.

    • Photo: Andrew Cairns

      Andrew Cairns answered on 17 Nov 2011:

      Yip, depending on the design they will either be anchored on both sides (which is easy to understand as it is how, for example, a table works, or they work on a complex cantilever system. If they are only anchored on one side or the other, then the opposite end is supported by the step below. This puts a twist strain on that step, which is kept rigid and in place by being securely anchored in the post or the wall.

      Here are some pictures of beautiful spiral staircases:

      Vatican City staircase, where there are actually two spirals inside each other:

    • Photo: Hayley Smith

      Hayley Smith answered on 17 Nov 2011:

      Yup, it’s all a nice balance of forces and tensions!

      The spiral stair case in St Paul’s Cathedral is quite cool (and it’s also where some of Harry Potter was filmed!) and just thinking there, there’s a fair bit of physics at St Paul’s, what with the whispering gallery and everyhing too…

    • Photo: Peta Foster

      Peta Foster answered on 17 Nov 2011:

      Yes i agree with everything thing said here and that staircase image is stunning Andrew! It is all about balance… otherwise pirates wouldn’t be able to hold out planks for people to walk 😉

Comments