I would like to design and possibly build an octagonal timberframe with no central post. The diameter of the building would be approximately 66'. Is this possible or am I nuts? The bents would form 2 concentric rings 12 or 14' apart supporting the rafters. The rafters would rise at an 8/12 pitch and be approx. 28' in length from the inner concentric ring. I hope this makes some sense. If not, please forgive me.
Thanks, Steven.

This is a certainly a large project with some significant challenges to make it work with all wood joinery.

A couple of considerations:

1. Where is this to be built? What are the applicable snow and wind loads?

2. The two concentric rings of posts help in providing structure to resist the outward thrust of the central roof section.

3. A structure the size of the "inner ring" has eight sides of about 15 feet each. This is a reasonable span, but approaching the limits of all wood connections.

4. The outer ring will be about 26 ft to a side. You would need intermediate posts,giving 16 posts on the outside walls. The extra posts cut the span to 13 ft which is a more reasonable span.

Interesting project. I expect it's possible, but is not a small undertaking.

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.

Sounds like you're on the right track. Keep us posted, and Good Luck.