The classic example of a ring stadium is the Calgary Saddle Dome which is a
round hypar structure. Another way to build this is to support the cover with
either poles or trees inside the ring. If trees are used, care should be taken
to put the same species in a ring around the center so that there are fewer
sagging places where the fabric is unsupprted. The tree species should be
selected so that the tallest species are in the center, the shortest around
the edges and even the shortest are taller than the outside ring height. Also
the trees should be of the type with a wide canopy to distribute the load,
rather than a tall tree with only one high point which will probably not be
able to grow straight up against the cover and will create high point loads in
the material.

A cover has thermal resistance because of the air on inside that isn't moving
of 0.12 m^2 * C / W and a thermal resistance because of the outside air
that is moving of about 0.03 m^2 * C / W for a total thermal resistance of
0.15 m^2 * C / W.
In winter, because of the low angle of incidence, about 0.2 of the sun's
radiation at 1,000 W / m^2 will go through a translucent cover parallel to the
gorund, so about the heating is 200 W / m^2 when the sun is shining. In winter,
the sun shines about 0.1 of the time, so the average heating is about 20 W /
m^2. The average temperature rise = power * resistance =
20 W / m^2 * 0.15 m^2 * C / W = 3 C
 
 

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