Wednesday, September 4, 2013

Spiral vs. circle coursing in the dome roof?

The corbelled dome we are building is made of a continuous course of narrowing spiral of flagstones  

You can see it better here in the outline.

We could have build it in a different way by creating separate rings of stone that lay on top of each other and get gradually smaller in diameter.
That would mean fitting the last stone of each circle in the space between the first and the second to last.

The spiral has the advantage of not having to do that kind of 'last stone' fitting on each row. 
But is it as strong? That is the question.


  1. So many excellent questions without absolute answers in this dry stone walling bit, eh? I like to look to structures in nature for the answers. Perhaps the spiral built paper wasp nest shows the way? Can't think of structure using concentric rings in nature but I'll bet some examples exist.

  2. Yes I think something in the style of Fobonacci is my preference too.

  3. The ripples are circular because the momentum is transferred to all the molecules of water around the stone, to accomodate the stone (because it moves water apart while falling down) they move outwards, conservation of linear momentum can be applied to this:
    When you throw the stone into the water, its momentum is acting downwards, when it hits the water, it's downward velocity is reduced, because linear momentum is conserved and because the stone also hits the water, the stone disperses its downward vector into several components acting horizontally. Thus the initial downward momentum of the stone and the momentum of the ripples in the water are conserved.

    Maybe why this is why ripples never come back...

  4. Are tree rings not concentric?
    Or wave length patterns?