Timber "A" Frame questions

[Lost in the Outback]

 

 [img]https://forestryforum.com/gallery/albums/userpics/32507/A-Frame_282929.jpg[

Hey Guys,
My 1st crack at building with beams and timbers. My building site is at the back of my 100 acres where the wood lot is. No road in  good enough for a truck, only atv.
I have searched high and low for information on structural requirements for timber frame, "A" frame structure.
My base is 18' x 18' resting on 8 stone mortar 12 x 12 pillars. The box frame beams are 8 x 8 eastern pine.
My questions are:
What are the least # of "A" frames I require?
What size beams should I cut for the "A"'s ?
Can I use a bridle joint for the top of the "A"s.
I borrowed a picture off of Google to assist in my explanation.
Thanks alot in advance.

[Chilterns]

Hi Outback,

Wayback in time I think that what you are referring to as "A" frames were called cruck frames and if this is the case then you will find quite a bit of practical information on making cruck frames on The Oxfordshire Woodland Group web forum where you should search using the word "cruck".

I cannot see the pic that you posted.

Chilterns

[PC-Urban-Sawyer]

...

I cannot see the pic that you posted.

Chilterns

You mean this one...

[Lost in the Outback]

That is it...yes

[danreed76]

I would think that for an "A" frame you should be able to start with a simple roof load calculation (forces implied by snow load) then figure out the size and quantity of rafter pairs to be built based on the desired/available species of wood.

The bridle joint (in timber framing typically referred to as a tongue-and-fork) should be acceptable as long as the bottom of the rafters are properly seated.  Seems to me that the calculations for an "A" frame would be just about the same as planning and designing a roof which will sit on the sill rather than a top plate.  You can find lots of good threads on here that will walk you through the calculation process, but as always it's good to have the final design reviewed by an engineer.

[Brad_bb]

I'm not familiar with "A" frames.  Is this for very high snow load areas?  Sizing of beams would depend a lot on angle, snow load, spacing between frames.

[Ljohnsaw]

My cabin will be build at 5,800' elevation in the Sierras and I have to build to 12' of snow (341 lbs/ft^2).  If I go another 20 minutes up the road (to 7,500-8,000') they use a LOT of A frame cabins. Only their slope is much steeper than the one pictured!  Probably because they see upwards of 20' of snow in a good season!   Usually very wet snow to boot.

As Danreed76 says, start with your snow load calculations and go from there.