Mark—

The milling of the posts and the backing angles on your hip rafters only requires a little figuring and the fabrication of a series of kick blocks for the bed rails of your mill.

I can not read enough into your writing to know much about your frame and reasonably comment on the specifics of how it should be configured, but will say this…

Your inner rings provide you your opportunity to resolve your thrust issues inboard of your plates. I don’t know that anyone has quantified the value of SB enclosure as shear walls and don’t buy into the notion that even good ones are reason to eliminate bracing.
In that I find a self aligning frame which is safe to walk while raising and someday safe to strip ( enclosure is in truth a maintenance item and should reasonably be expected to have a shorter service life than the frame it’s self ) I choose to put braces anywhere they do not interfere with millwork or introduce tension I do not wish to impart.

Steel is always a fallback, avoid treating ( and point your engineer towards same ) the main plate line as a tension ring and it can be avoided or used soley as a failsafe.

Again look to the inner rings.

do we need more bracing in the radial plane or the plane which follows the circumference? or, should there be the same number in these two planes?
Also, should all the rafters be on radial lines or is a pricipal/purlin system more efficient?

thanks again,
-Mark.

Will,
I wonder why you suggest not to rely on plate? I would say main plate can and should be treated as tension ring when there is proper tension joinery used.

Michal

Hi Mark,

I am currently working on rebuilding a large post mill which is fitted with a self supporting octagonal roof on a brick roundhouse and it is not permitted for the roof to lean on the centre post !

Octagonal buildings are not that common today and the main ones that can still be easily seen are probably smock windmills. These can have several storeys coming off 8 long continuous slanting posts sometimes arranged in iregular polygon fashion.

The ultimate octagonal building is the lantern at Ely Cathedral see Hewett - English Historic Carpentry page 160 -164. This has 50 foot high posts standing on a 30 foot radius.

You might also want to check out the carpentry on the Globe theatre which is a 20 sided polygon. I seem to recall that there was an article in Joiners Quarterly about this project and I believe also in Timber Framing. Check out the past issues. There is also a chapter on the construction of the Globe in the book Shakespeare's Globe Rebuilt (isbn 0-521-59988-1.

I am about to start work on an energy friendly timber framed house which will have 5 segments of a 16 sided regular polygon arranged in an arc to catch the sun's energy.

Why not post a sketch of your project on the website. Like Will I am struggling a little to visualise the concept.

Regards

Ken Hume
http:\\www.kfhume.freeserve.co.uk

Pardon the lapse, TTRAG and a raising demanded most of my time the past few.

Interestingly, the first polygon I worked on was a ill-fated attempt to replicate a twenty sided Globe with and under the direction of a friend of Ken’s, Paul Russell, the man I had the good fortune to learn scribe from many years ago. Ironically I picked up a long out of print tome on the Theatre in an antiquarian bookshop just yesterday

Mark –

Brace both the radial bents and the inner circumferential ring liberally, the main ring, to the extent that your window and door schedule allows. This is also where you can both negate and redirect thrust through strut/s to the inner ring where it is best resolved

Common purlins are an excellent step towards redirecting and concentrating thrust to the principals/hips.

Michal –

I’m afraid we will have to agree to disagree on the tension ring issue, however I must qualify that with a big ‘ole “in my opinion”

IMO good timberframe design demands the elimination of all possible tension joinery on the drawing board, I choose to do this, in that there are few joints available to us which deal with tension well.

The best case for a polygonal ring, are daps with material projected on beyond the vertices for ample relish. Mark is free to do this even on the main ring, simply by choosing to deal with the work necessary to cut and fit the SB enclosure around the relish, he is freer still to do this on the inner rings.

When we have the freedom to direct thrust away from one joint and in the redirecting now impart it not as thrust, but largely as a dead load to a point in the frame better able to deal with it, why not take advantage of that freedom ?

hi there
i've photograghed three of the design pages with my kodak digital camera and posted them to webpages....

here are the url's

http://www.geocities.com/markola17/photo2.html?1080148218620

http://www.geocities.com/markola17/photo3.html?1080147420170

i appolgise in advance for the quality of the images but these will definitely help those interested to visualize the building.
the design now officially has a center support(will either be masonry or wood) and the inner ring of posts and beams will move to the best placement between the center support and the 16 foot radius ring(8 or 9feet radius?).
again, many thanks to all who are writing, this is an interesting design and hopefully will be worth the effort.
-Mark in Ontario.

blast it
yahoo has cut me off....
i couldn't access the photos because i have exceeded my data transfer..so the above links may not work for you
SORRY!
i'll work on it
-M.

will....
excuse my ignorance but what is a "dap"(s)
-Mark.

another possibility for the joinery that keeps nagging at me is to place the 8 hips or principal rafters directly on top of the posts and move the beams down a bit(6inches minimum), getting away from the lack of relish at the top of the post...but how would it be assembled? you would be fine till you got to beam number 8 and then what? this is not a bent it is a ring so assembly is an issue
perhaps there is a lap joint for the beams?
-M.

Nothing to forgive, the ignorance was mine, in useing a regional term, habit had me forrgetting it was so little used.

Halveings - simply letting one timber into another

Underused, yet highly effective