andrewjsmith
Mechanical
- Oct 24, 2015
- 15
Hi Folks - I am a professional electrical engineer, but as a student did a common 1st year with Civils, Mechanicals & Aeros, so feel that I should be understand some basic ideas in civ. eng. But this one has stumped me.
I became interested in corbelling after crawling into the wonderfully preserved (or restored) Neolithic long barrow near Wellow, Somerset ( Sitting in the final chamber, and looking up to the corbelled vault of the roof, I was not exactly anxious about my safety (it had stood for 5000years, so would presumably last a few more minutes), but uncertain about how the system works. The Wikki article on corbelled arches includes this in the lead "The technique of corbelling, where rows of corbels deeply keyed inside a wall support a projecting wall or parapet... " suggests to me that the idea behind corbelling is that the projecting slabs or blocks act as cantilevers, the force applied to their outer part being counteracted by the moment of the weight of the wall above the point of insertion, this weight acting on the embedded part of the projecting corbel. If this is the basic principle of a corbel (the deep insertion being vital for stability), then how does the Gallerus Oratory support itself ? In this structure the side walls lean inward, but there are no abutments or mass of masonry above the 'corbels' which could provide the required counter-moment. Does this type of structure depend on a different principle ? For example, do the two opposed sides lean against each other and thus support each other as the two sides of a true arch do ?
Can anyone outline the conditions for stability of these two types of structure ? (i.e. corbels having a mass of masonry above the projections, and those without).
I became interested in corbelling after crawling into the wonderfully preserved (or restored) Neolithic long barrow near Wellow, Somerset ( Sitting in the final chamber, and looking up to the corbelled vault of the roof, I was not exactly anxious about my safety (it had stood for 5000years, so would presumably last a few more minutes), but uncertain about how the system works. The Wikki article on corbelled arches includes this in the lead "The technique of corbelling, where rows of corbels deeply keyed inside a wall support a projecting wall or parapet... " suggests to me that the idea behind corbelling is that the projecting slabs or blocks act as cantilevers, the force applied to their outer part being counteracted by the moment of the weight of the wall above the point of insertion, this weight acting on the embedded part of the projecting corbel. If this is the basic principle of a corbel (the deep insertion being vital for stability), then how does the Gallerus Oratory support itself ? In this structure the side walls lean inward, but there are no abutments or mass of masonry above the 'corbels' which could provide the required counter-moment. Does this type of structure depend on a different principle ? For example, do the two opposed sides lean against each other and thus support each other as the two sides of a true arch do ?
Can anyone outline the conditions for stability of these two types of structure ? (i.e. corbels having a mass of masonry above the projections, and those without).
