Another Mortise and Tenon,(M+T), Question 2

[Robbiee]

This barn I am reviewing will be constructed at a different location than its original one. When checking the mortise and tenon connections, The pegs, ( wood dowels) are not adequate to resist the uplift loads at the posts to purlins connections. Can I rely on glue to transfer the loads? If the tenon is fully engaged, its capacity in tension is adequate. The cross section of the tenons is 1-1/2" x 7". I know glue is used with M+T joints but not sure if it is used in large joints of barns/houses.
Any comments are welcome. Thanks for the help.

 

[msquared48]

Not according to the IBC unless it has been tested by a testing agency.

I have seen some local jurisdictions accept glued joints though, but very few.

This is a sticky area.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[Robbiee]

Thanks Mike. I wonder what would you do without using steel straps or plates. I want to keep the wood clean of any visible steel.

 

[msquared48]

Do the dowels fail in shear or bearing?

Can you post a picture of the connection you are working with?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[MiketheEngineer]

Call an Amish Engineer - they do this all the time!!

 

[Robbiee]

Dowels are failing in shear. Please see attached.

 

[dvd]

Seems a little far-fetched, but I'll ask anyway: if the dowels fail, but the hole doesn't tear out, is it possible to use steel/aluminum dowels? Maybe cut short of the wood face with wood plugs at the face for cosmetic effect.

 

[msquared48]

Can't install lag screws through the 8X8 beam into the 8X8 column due to the end grain connection of the column, so...

I would seriously think about either increasing the capacity of the wood dowel, either by diameter or species or both, or use a metal dowel with wood cover plates at the outside of the 8X8 beam.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[dik]

Can you use slightly larger dowels and use a real hard wood... I've replaced dowels with ironwood pins (hophornbeam) for added strength. On one project, I had intended the pins to protrude... contractor (master carpenter trained in Switzerland) had recently picked up a Japanese pull saw and cut the pins off flush. Can you use a steel pipe with a wood plug in the end?

Dik

 

[BAretired]

If the Queen Post is not too long, you could drill a hole through the beam, post and purlin and use a threaded rod as a tension member, completely hidden from view by the 8x8 post.

If it is too long, you could laminate two 4x8 posts with a groove to receive the rod in the middle.

BA

 

[roy835]

Check out the Timber Frame Engineering Council.

Link

TFEC-1 provides guidance on mortise and tenon joints.


Larry Reynolds

 

[dik]

LLR... excellent link...

Dik

 

[Robbiee]

Thanks all for your help. The link LLR provided is excellent indeed. Out of the options provided, the owner ended up accepting adding steel plates at a couple of locations.