Hey All, the octagon topic that was lost has got me thinking.
What do you all think.

Post to hip connection
Boss pin (no post running to the ground in the center)
Overhanging hips over the posts

How could you tie this with all the hip rafter thrust? Would the boss pin have to be short enough where you could half lap ties from post to post? One set half-lapped and the other half-lapped above? Do your ties half to intersect the boss?
Any ideas?

hmmm, this looks familiar

Welcome, Kyle. Any suggestions?

put some wedged dovetails on the ding-dang thing

Hi Mo, being Easter morning and all, I thought this looked a lot like a place for some steeple work. Maybe a crab with rafters up to the top of the King Pin. You could use some wedged dovetails for sure.

Here is something along this some line. Someone just brought up the question, Why do we use the term King Post? A post is a member in compression. Shouldn't it be called a King Pin or Boss Pin. The "Mob" must of borrowed the term from the building industry. And now we are borrowing it back. Tim

Is that a sketch up drawing... if so how do you post them? I've got a modified english tying joint that I did for a 12 sided polygon.

Carlos

Would you consider a ring of top plates on top of the posts, instead of connecting the post directly to the rafters? Then you'd have a "tension ring" formed by the plates. Set the rafter feet on the plate. CB.

Thanks, for the input.

Kyle, did not think about the wedged dovetail. I wonder with significant tension from a heavy load roof if the interrupted ties would work? But I suppose there aren't many options at the boss pin...

Carlos, Under File Menu, Export: Export 2d graphic and then post the same as a picture. If you don't know how to do that you can search the forum.

Daiku, Yes that seems like a good idea. What is then the best way to describe the post, plate, rafter area and its connections? Would you half lap the plates? What would then be the best way to connect the post to plates?

I think a "backed post" would probably be a good idea as well so you would not have un-level mortises and housings on the posts for the braces from plate to post and you would not have to mortise on an angle.

I like the idea of the tension ring around the top of the posts. I wonder if it is possible to have a tension ring at the bottom and a compression ring at the top, and eliminate the need for boss pin, ties...

Here's a pic of an octagonal frame I built (a scribe workshop - with the help of many) for a local museum back in '01



It is built with plates, though in this instance the plates do not act as a tension ring, the thrust is redirected and resolved at the inner ring, and tension and tension joinery was avoided to every degree possible.

It is possible to solve complex issues in the design phase, to build a traditionaly joined polygonal building.

Keep on keep'in on and playing with ideas.

That's fantastic, Will! That one gets filed away for future reference. CB.

That is fantastic! I bet that was fun to build and enjoy.

"It is built with plates, though in this instance the plates do not act as a tension ring, the thrust is redirected and resolved at the inner ring, and tension and tension joinery was avoided to every degree possible."

Will, Could you explain in laymen terms how the thrust is redirected? Is the thrust applied to the inner octagon and posts and then through the dragon beams (is that the right term?) and bracing the thrust is reduced or eliminated?

Thanks, mo

p.s. Tim, forgot to ask what do you mean by "crab"

Mo, do you recieve Timber Framing? If so check out issues 83 and 87 and the related steeple work. I keep going over them. and am trying to get into some local churches to see how they are made.

Dragon beam is the first thing that came to my mind as I scrolled down the page. Next came hammer beam. A Yurt uses a cable as a tension ring, a whole different thing though. I see each dragon beam section as a truss and they set on the inner and outter post and stand as a simple unit. Just place them all together pointing to each other. Hey, no roof board. Tim

Here's my idea for a modified english tying joint. This is done for a dodecagon (12 sides) it would definately not work for a octagon because the angle is more acute and the spline would run out of the top plates. I'm planning a dodocagon right now with a engineer and we have opted to a hidden bolt (much to my dismay). I guess sometimes metal is stronger than wood!!

Carlos, sketch up is a great communicating tool isn't it? Did the desinging of this joint force you to go to the 12 sides as your were mentioning the spline and the angle of the plate to post would not work in an octagon? Are the splines carrying all the weight of the plates? What are the two plumb rectangles at the end of the plates? Thanks, mo

Tim, yea I have those somewhere in a stack I'll try and dig em up and take a look.

What about no boss pin and no ties? Will these work as buttresses?

Mo

The two rectangles were to be housed into the rafter to help with the weight of the top plates and counter twisting. However they were only 1/2 inch in depth in my model, even then I wasn't sure about the raising process!!

We went with 12 sides as I wanted to keep the sides at exactly 8ft in length (plywood, drywall etc..). I used a polygon calculator on the net, entered 8ft sides with about 700 sq feet and in spit out 12 sides.

By the way thanks for the explanation of how to export the 2d drawings from Sketch-Up !! I've been wondering how to do that for a while!!

Carlos