Historical precedent for this style of frame?

[David M]

Hey guys,

 Looking over one of the THQ plans I came across a king post truss version I am not really familiar with. I can't seem to find much historic precedent for tying the principle rafters right into the posts like that right along with the ties...

Is this as contemporary as I think it is?  

None of the plans being "engineered" leaves me a bit to wonder how this truss acts under load vs the standard method of proper tying joint in the tie/post.

Feedback would be much appreciated.

Thanks!

12×16 King Post Timber Frame Plan - Timber Frame HQ

[Don P]

Not the strongest way to do that. The horizontal roof thrust is being restrained by the pegs, or, if the tie is designed as a beam capable of supporting the king as a post then that can support the top chords. It is small, I quickly looked at the next larger size a 16x24, it looks like the same thinking. I'd have an engineer check it.

[David M]

Would replacing that iffy simple tenon in the king post with a 2" wedged half dovetail go a long way towards addressing that issue in your opinion?

[Don P]

Not really. I really like the overall look of the structure. My concern is with the bottom chord tie to top, rafter, chord connection. In this small building it is probably ok and gives a nice overhang. If larger or in high snow loads I'd probably use some steel in the joint.

Another thought would be to run the bottom chord across the posts, cantilevering it out to form the overhang and then notch the top chord into it. You couldn't cantilever far without that getting into trouble as well. The post in this pic could have been slightly inboard of the heeljoint, but I'd want an engineer to look at it if it was more than about the depth of the bottom chord, less if the loads were high.



Another way I did a small frame with a large overhang was to basically balance the rafter on the post hoping to greatly reduce thrust by that balancing act.  That idea was not mine, I've seen similar thinking in some barns. I've showed and explained this to a couple of engineer friends, they didn't run screaming but I didn't ask them to review it.



  

[Brad_bb]

I'd  direct your question directly to Bryce at TFHQ.  My bet is that it was engineered by Firetower.  So he may be able to provide you that if it's not automatically included as stamped plans.

Bryce designed those frame plans.  He's been in timberframe design for quite awhile.