Orion/Baker on sun 1 feb 98
Jenni,
Catenary arches are taller than they are wide -- they have sort of a
half-egg shape. (You've heard the old adage that the "egg shape" is
perfect in terms of strength.)
Sprung arches generally have a true circular shape -- ranging from a full
semi-circle to just a part of a circle (an arc). As I was saying the other
day, the flatter any arch is, the more of it's weight is transferred
outward <----> at the bottom. The term "sprung" arch just refers to the
amount of support the arch needs to stay "pinned in" or "contained" between
the walls at the top of the kiln. Properly sized, a strong outer wall can
contain a "sprung" arch without a metal superstructure or welded frame.
Good questions!
Ellen Baker - Glacier, WA
Vince Pitelka on mon 2 feb 98
>the walls at the top of the kiln. Properly sized, a strong outer wall can
>contain a "sprung" arch without a metal superstructure or welded frame.
Ellen -
You need to explain this much more thoroughly, or you run the risk of
getting novice kiln-builders in deep trouble. The only way a vertical wall
can absorb the outwards thrust of a sprung arch WITHOUT a metal frame or
externall buttressing is if the side walls are EXTREMELY beefy - we're
talking MANY MANY courses of bricks to provide the stability and rigidity
needed. This simply is not space-efficient or cost-effective. A metal
frame is such an easy and practical solution, and as had been pointed out,
the simplest frame can be bolted together with threaded rod.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
William Brouillard on tue 3 feb 98
Just a short comment on arch support for catenary type arches.
Th notion that catenary arches are stable with no additional
support is not always true. Kilns are not static structures, they
move when heated or cooled. Not all of the expansion is equal and not
all parts of the kileturn to the position they held prior
to being heated.
Sometimes a kiln will walk. Pressure from expanding
front and back walls and the base of the kiln will push the kiln into a
wider stance when hot. When the kiln is cooled it may not return to
the original size. The movement may be small and happen over years.
In practice many catenary type kilns are buttressed or incorporate
some metal framing to control movement of the base. The amount of
framing or buttressing can be minimal. Can a catenary be built with
out it ?. Yes it may last for years with out any failure. Most of the
catenarys that I have built or have seen use some type of frame or
support. In most cases it amounts to a small sprung frame at the
base of the kiln.
My two cents BB
--
william brouillard
1011 literary road
cleveland,oh.44113
ch151@cleveland.freenet.edu
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