On Thursday, September 5, 2013 10:08:48 PM UTC-7, John B. wrote:



If you make the 1/8" a very flat cone shape you can probably eliminate

support beams.

*** I was thinking about something similar. In order to eliminate support beams, I believe it would have to be a dome. Something I simply cannot make. But a cone
shape would help. It would effectively halve the span. The tip of the cone would
be loaded in compression.

I found a video on Youtube of digging a well and fabricating a cover in a 3rd world country: http://www.youtube.com/watch?v=eM3gVpNflVE. For the cover, they basically made a domed pile of dirt, a wooden ring and dumped concrete on top, with some reinforcing steel wire inside. I am not confident of my ability to create something like this in concrete - light enough for say four men to lift, and yet strong enough for kids to play.

- Jerry Kaidor