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Author Topic: Issues with reduced tenon width?  (Read 360 times)

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Offline treemuel

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Issues with reduced tenon width?
« on: August 16, 2021, 09:11:07 PM »
I'm currently designing a 24x24 timber framed garage/workshop with an attached 12x24 carport. The structure has a 12:2 shed roof, but the carport roof will be lower than the main roof. I'm seeking input on how to attach the plates for the carport. Because of the multiple joints coming together in a tight space (opposing tie-beams w/ a spline joint, brace, and carport top plate), my current plan is to fit the plate tenon in below the brace and above the spline joint, but this would seem to require reducing the width of the plate tenon to 6" (for an 8x12 plate). I calculated the minimum bearing surface for the anticipated load at 13 sq. in. So a 1" housing and an 7" long (maybe I could even reduce this to 6"?), 2" thick tenon, should be sufficientas long as the reduced tenon width doesn't cause any issues. Also since it's a plate for a shed roof, I wouldn't expect the joint to experience much tension. Does this seem like it would work or are there other ways I could fit the joinery so close together? (I've tried moving things around, but everything I move seems to create a conflict between joinery somewhere else in the frame.) Also, is there some other load calc I could run or rule of thumb that would relate to this?

I attached an x-ray picture of the proposed joinery and an overview of the frame.  

Thanks for any input! 

Offline Don P

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Re: Issues with reduced tenon width?
« Reply #1 on: August 17, 2021, 07:13:13 AM »
Do the girts have to be at that elevation? Do they have to be continuous and splined at that elevation? What is catching the siding up high?

 Vertical shear of the cross section would be another check. With the beam tabled I doubt it is an issue. 
The future is a foreign country, they will do things differently there - Simon Winchester

Offline treemuel

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Re: Issues with reduced tenon width?
« Reply #2 on: August 17, 2021, 08:41:52 AM »
Thanks for the response, Don.

The splined girts (is it inaccurate to call these tie beams since they're not resisting outward thrust?) don't necessarily need to be continuous or at that exact location, but it works well with overhead height in the center of the building, window and door height, and brace locations. Also allows for a possible half loft. 

The building will also be insulated with a simple exterior stud wall (which will carry the siding). And for the interior wall boards I'll probably add girts in line with the roof angle that drop into the plates/beams.

I was hoping that the tabling of the beam would be sufficient. So would the vertical shear to check be where the tenon meets the beam? In which case, it would be perpendicular to the grain, right? Seems like that shouldn't be a problem, but my engineering knowledge extends only as far as using online calculators :) 

The other question I forgot to ask is: I didn't include braces on the building side of the carport (due to having a stud wall there and wanting to maximize overhead height in the carport), but it seemed unnecessary with the building itself resisting any movement in that direction. Is that reasonable?   

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