PE - Ger structure

[Corun MacAnndra]

Mira wrote:
>
>For the record, my roof poles are square. The ends that go into the roof ring
>are cut at an angle, thus 'locking' them in so they don't twist.  I have
often
>wondered if the yurt failures I hear of sometimes aren't a combination of
>various factors:

If you put square poles into a square hole, and they fit tightly, then they
don't really need to be at an angle. They're not going to twist. The
problem I pointed out to Todric comes with the ubiquitous 1x2 flat (okay,
for the record rectangular) poles in an ill fitting hole. I don't know if
you've come across this type of design out your way in An Tir, but in the
Middle and the East this design has permeated many yurts. It's an old
design as Todric pointed out, and, if done right, can work. But if any roof
ring and pole arrangment is done Right<tm> then it shouldn't need the extra
supporting ropes tied up near the roof ring to prevent twist because it
won't twist. This is the whole thrust of my comments.

>--too low a pitch to the roof.  From what I've seen, the Mongols have one
of the
>lower pitches to their roofs of all the nomadic, lattice-walled tent
users, and
>I've seen a lot of gers in the SCA that have a lower pitch than the Mongol
ones.

Yes, too low a pitch can cause problems.

>--Bad setup--door into wind or not enough ropes over top or not staking ropes
>down in stormy weather.

Uneven ground can be the biggest cause of this. Though you can set up a ger
on uneven ground the lattice will ten to pantograph, that is, take the
shape of the ground. This will make one wall higher or lower than the rest
and the roof will not fit right. This can be recitified by cinching up the
outside belly band Really Tight. For evidence I point you to the one yurt
that was in our camp this year (Mira, you saw it, the one across the
compound from mine). It had a serious pantograph (compounded by a couple of
things wrong, but not helped by uneven ground). Tying it up tight kept it
up even in the big storm.

>--A Really Big Wind That Will Not Be Denied.  We just had a funnel cloud come
>through south of my town, which demolished a nice new barn...tornadoes
happen.

I don't think we're in Kansas anymore, Toto. In other words, don't piss off
Tengri.

>--too few roof poles--so many people overengineer and use fewer, larger
poles.
>This changes the stress distribution.

Indeed. Even the right number of poles but made of too heavy a material can
change things radically. Last year I tried an experiment with using square
poles that had been rounded and tapered on both ends much like what one
sees in some Mongolian gers. It was a nice idea, but I used pressure
treated wood which is nearly twice as heavy as its untreated counterpart
would have been. This was not a Good Idea. I've gone back to closet poles.
I've proven over twelve years that they work well. I've never had a roof
cave in on my in the heaviest wind (and there have been some doozies come
through Pennsic in that time).

>--Insufficient exterior tension.  This is a biggie, because I see a lot of
yurts
>with old rope or just decorative tension bands, sometimes improperly
placed too
>far down the wall.  My yurt has a steel core clothesline, covered, the
weaves in
>the top of the derim (khana/lattice wall).  I think those bad tension band
>problems are another reason so many yurts HAVE such a low pitch to the
roof--it
>is busy pushing the wall out!

Here is the biggest problem. So many people put in only what I call a
girdle cord. This is a cord that weaves in and out of the khana at the top
and makes and keeps the whole round before you put in the roof poles. This
is insufficient by itself in most cases for proper tensioning of a ger. A
few years ago I went away from the more traditional (for the SCA, I have
seen no proof nor lack of it for this having been done in period) weaving
in and out and since I'm already putting the khana together with hex head
bolts I simply replaced the ones at the top with eye-bolts with the eyes
inwards. I attached a small cleat to each side of the door frame and I lash
my girdle cord (a simple poly rope) to one, lace the rope through the eyes
and cinch and lash to the other cleat. Nice and tight. But once my canvas
is up I have a canvas belly band eighteen inches wide that I pass through a
slot in the door frame, lash to the khana and wrap around the entire ger,
over the roof and wall canvas near the top and just under the roof poles,
passing through a slot on the other side of the door frame and lashing to
the khana there.

What this last bit does is this; There is downward pressure from the weight
of the roof ring and poles against the top of the khana, forcing it to bend
outward from the top. By tying the belly band on you create an opposite
upward and inward pressure against this weight. With the two forces working
against one another you get a nice, stable structure (Mira, I know you and
Todric know this, but this is for the benefit of those who don't).

Also keep in mind the most important thing here; In the SCA we do not build
yurts with the same density of poles in the lattice as is done by the
people who live in them. The yurt from which I derive the bulk of my
research was a Khazhak yurt, 15 feet in diameter (the average size of most
SCA yurts). The khana stood 5'6" in height when strecthed out and was made
of six sections lashed together and to the door frame. The poles were
drilled to accept rawhide strips to tie them together and were about 4.5"
center to center, or about the breadth of a loosely opened hand. Each pole
was about one inch thick by eight feet long and appeared to be a sapling
trunk, probably of arctic willow. Most khana you see in SCA yurts is
drilled 12 inches c-c. So right from the outset the khana on the Khazhak
yurt was three times as dense. This also made for nearly 100 roof poles,
all of which were the same thickness and material as the poles in the khana
(i.e. one inch thick arctic willow).

The roof ring was 57 inches outside diameter and made from three sections
of what appeared to me to be tree trunk, lap jointed, bent in a curve and
joined by two steel bands at each join (total of six bands). The roof poles
were probably close to ten feet long. These were cut square for about four
inches on the end that fit into the roof ring, and these went into square
holes. The other ends were shaved flat for about 24 inches of their length
and then bent so that the poles fit flat against the outside of the khana
where each was tied by a small cord of woven or braided yarn. This raised
the wall a good exra eighteen inches, and with the gentle curve the inside
was very roomy and nearly cathedral-like. The roof ring was up about 12
feet or more and as big as it was made a huge skylight.

The whole ger was held together with nothing more than woven or braided
cords or bands. All the felt walls (some of it three quarters of an inch
thick) had three inch wide bands of multi-coloured woven yarn bands on the
upper corners which were thrown completely across the roof and tied to the
khana on the other side. On the outside were many bands of woven yarn, the
largest being eighteen inches wide).

Some pictures of this ger can be seen at
www.clark.net/pub/corun/mongpage.html. The page is horribly out of date,
but the pictures are nice. One of these days I've got to update the page.
This was shown at the Nomads of Eurasia tour that came to the US from the
(then) Soviet Union in 1987. I have to thank the Academy of Sciences in St.
Petersburg for the allowing me to get into this exhibit after it closed. I
spent two days taking notes and measurements.

Corun


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