Grigg,
Thank you for your reply. Yes, this will be a mammoth undertaking. I have some very crude plans which are in the fledgling stage. If it ever reaches the point where it could be built I would most certainly need the expertise of various engineers to solve the snow/wind loads and the myriad other intricacies involved. As to your point of there being intremediate posts: I have planned for there being 2 on the inner concentric and 3 on the outer. The rough plans I have now consist of over 650 joints on the main frame alone. Perhaps this could be pared down, I don't know. I tend towards overbuilding. Perhaps if I ever get these plans done I could present them to someone to give them a looksee and tell me if it can be done( or should be!). Thanks again, Steven.