DoN. Nichols wrote:

Hmmm ... is there a collection of calculations for the belt
world which appeared in a few science fiction books? IIRC, that was
rather well calculated out. The diameter was a lot larger, but this
could give a starting point.

The structural ring of Ringworld was made out of
scrith, not granite. If you're going to do
outrageous designs it helps if you can make up
your materials as you go along.

Ringworld Engineering...
http://larryniven.wikia.com/wiki/Ringworld#Scrith