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Triple Bypass Joint

Started by John Sheppard, June 07, 2015, 01:50:55 PM

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John Sheppard

Hi all,
   I have a question about the triple bypass joint.  I was looking at the Tie and Plate joints on the Timber Framers Guild's site.  I have a 12" x 12" post and 10" x 10" Plate and Tie.  I want the Plate and Tie to be relatively in the same plane since I have a doorway that will be opening onto the given location 2 1/2 feet away from the Tie beam this is elevated 2' off the pad with steps leading down to outdoor patio.  So I am trying to get as much height into the tie beams as possible.  The bottom of the Plates will be 10' off the ground.  I found the Triple Bypass corner tying joint, specifically Figure 30 on page 16.  I would like to adapt this to my particular timber configuration.  The joint shows 6" of 2" x 4" tongue for each of the joints tying to the post.  It doesn't show an assemble joint for this particular bypass, but that would mean that the tie beam hangs over the post by 2".  With my tie's width it would mean a 4" overhang.  Is this too much?  Would it introduce any twisting stresses into the tie beam?  Should I narrow the end of the tie to maintain a 2" overhang?  If so, what does that do for load capacity of the beam?  In addition, should I notch the post so that at least 2", or better yet 4", of the un-narrowed ( is that even a word? ) width of the tie beam is supported by the post?  This would still give the plate the same amount of support I think?.

Thank you for your advice in advance,

John Sheppard

Chilterns

Hi John,

This is quite a difficult problem to understand for most never mind try to resolve.

I have consulted various photographs that I have on file re actual examples of this joint and note that most of these do not have an identical plate and tie section with the plate more usually being much smaller and laid flat. If it were possible to post links on this forum to my photos I would do that but this is prohibited and so I am not able to help you as much as I would like.

It should be possible to reduce the section of the tie beam towards its end so that both the post and tie are fair faced without compromising the structural capacity of the tie but reducing the effective thickness of the plate in the area of the joint by notching will potentially result in difficulty in driving post to plate pegs.

You need to consider quite clearly the procedure (order) that needs to be followed to assemble this type of joint which will generally require the layout and joining of the tie & plates before dropping down the whole assembly onto the posts and in particular the various clearances required to drive pegs.

A person who has been investigating this joint in some detail is Jan Lewandoski and so you might want to try getting in contact with him.

Chilterns

John Sheppard

Chiliterns,
   Thanks for the reply.  I wish there was some other way to get the height out of the tie beam that I need because this is a complex joint in both manufacturing it and assembly.  As it is, my posts are already 10' tall. The doorway leading down is offset from center so a hammer beam wouldn't work either.

   I would love to see some of the examples that you mentioned.  You say that most of the ones that you have seen don't have identically sized ties and beams.  Is that most, or all?  I'll see if I scan the joint drawings that I have made and post up here.  With the same size beams, if I don't thin the plates on the end it would mean that the plates would sit a few inches higher than the ties which I don't mind.  I just can't deal with them being a foot or more higher than the ties.
   
    As far as assembly of the joint, here is what I was thinking.  If I make the seat for the tie 4" in depth and the tongue from the post to plate 4" in depth.  it would allow me to put 4 1/2" blocks under the plate and 8 1/2" blocks under the ties.  It may not even be necessary to put blocks under the plates and just rely upon the blocks for the ties.  Then using a 4 - 3" x 10"'s the same length as my tie beam, screw them to each side of the gable end posts about 14" - 16" below the bottom of the tie.  And using another 3" x 10" run it the same direction as my plates.  This should keep the post from spreading in either direction and give me a platform from which to use bottle jacks to lower the beams onto the posts.   The trick will be to keep the ties from wanting to slide in either direction when sliding the plates onto the tie tenons.  Haven't figured out how to do this yet.  I could probably use braces from tie to the 3" x 10"s that should prevent this.

    Then, with 20 ton bottle jacks on each of the 4 corners under the ties, I should be able to raise both ties and plates a quarter of an inch and remove the blocking.  Now bottle jacks aren't the most precise piece of equipment when it comes to letting them down so it may be necessary to step down the block sizes down an inch or so at a time.  This would allow me to not have to be so precise with letting down the bottle jacks in unison.  Just lower each gable end down onto the blocks. Then jack each corner back up a quarter of inch. Remove blocks and replace with the next size down. Rinse and repeat until fully seated.  Sounds good in theory but you know what they say. In theory, theory is great but in practice, practice is better.

    That is my quick initial thoughts.  I could be totally wrong and hopefully the good people on this board will help me discover the errors in my thinking.  I will try contacting Jan Lewandoski  to see if he can provide any guidance. 

John

PC-Urban-Sawyer

Quote from: Chilterns on June 08, 2015, 02:19:23 AM
... If it were possible to post links on this forum to my photos I would do that but this is prohibited and so I am not able to help you as much as I would like.


Chilterns,

The "prohibition" against posting links to your photos is in reality not a prohibition. All you have to do is understand and abide by the rules and procedures the forum administrator has established. The purpose of the rules and procedures is to ensure the integrity of posts in the future, preventing the dreaded "X" that you see so often on other forums where someone has linked to a photo stored at some other site and then later something has happened to make the photo unavailable. Here the photos get uploaded to your gallery on this site and the site then ensures that the gallery gets backed up during normal site backups.

The procedures are detailed here: https://forestryforum.com/board/index.php/topic,61788.0.html

Also, just in case you are concerned about the issue, the your copyrights to your photos remain intact, you are just giving the forum license to have and display a copy on the forum.

I'm sure many of us would like to see your photos and would benefit from them. Why not take a crack at it and if you run into any problems following the procedures just shout and someone will help.

Herb

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