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#33751 - 07/01/16 10:44 AM Mid Span Beam Joinery Question(s)
N_Butler Offline
Member

Registered: 06/30/16
Posts: 6
Loc: Maine
Hi all. I've been watching this forum for a long time as a result of my google search hits and finally decided to join and ask some of my own questions directly. I'm in the process of designing and building a barn (for myself) with a mid-span beam roof system which will support common 2x rafters. While working out my scarf joint locations I've been wondering why you never see beams at the top of a post, joined to the post faces instead of set on top, similarly to beams part way up (such as with floor support beams). I have seen a photo of such a system but I'm left wondering if the bending moment would be simply translated through the post and into the adjacent timber, which would move the problem from the eliminated scarf joint to the spline or tenons at the post (where there would conceivably be more bending stress).

This would be attractive to me because I could order and handle shorter timbers and eliminate the scarf joints altogether; all good things for me as I'm an amateur on a budget that allows for limited equipment support.

A wordy first post that could benefit from pictures I know, but I haven't yet figured out how to add pictures (working on it).

My apologies if this has been covered in a previous post, I did a history search but didn't find anything that quite addressed this.

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#33752 - 07/01/16 08:20 PM Re: Mid Span Beam Joinery Question(s) [Re: N_Butler]
Jim Rogers Offline

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Registered: 03/14/02
Posts: 1605
Loc: Georgetown, MA, USA
To post pictures here, you need to have them uploaded to some other picture hosting site. Once uploaded there you can insert the photo image tag in the body of the post and it should show.

Traditional timber frame design has the plates above the post so that the rafters sit on the plates. Having one layer of timbers going from eave wall to eave wall (the tie beams), and other layer of timber going gable end to gable end (the plates) creates a "grid" of timbers that makes the frame very ridged.

If you join shorter timbers to the sides of the posts (interrupted plates) this is more of a modern design method.
As long as the joinery is strong and true it may work for you.

Jim Rogers
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#33753 - 07/01/16 08:54 PM Re: Mid Span Beam Joinery Question(s) [Re: N_Butler]
N_Butler Offline
Member

Registered: 06/30/16
Posts: 6
Loc: Maine
Thanks! I'll probably stick with the more traditional approach and simply locate my scarfs carefully. There's likely good reason it wasn't and isn't often done the other way.

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#33754 - 07/02/16 07:20 AM Re: Mid Span Beam Joinery Question(s) [Re: N_Butler]
TIMBEAL Online   content
Member

Registered: 12/10/07
Posts: 1875
Loc: Maine
There is a rather lengthy thread on interrupted plates. Don Perkins contributed to it. Yes, it is more of a modern joinery solution but has a strong historic approach in the New England area as well.

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#33755 - 07/02/16 07:22 AM Re: Mid Span Beam Joinery Question(s) [Re: N_Butler]
TIMBEAL Online   content
Member

Registered: 12/10/07
Posts: 1875
Loc: Maine

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#33756 - 07/02/16 10:37 AM Re: Mid Span Beam Joinery Question(s) [Re: N_Butler]
Jay White Cloud Offline
Member

Registered: 11/06/08
Posts: 479
Loc: Vermont
Though not common, there is a number of vintage timbering systems that tend and/or have eliminated an abundance of long members, as Tim as given a great example of one. So though not common, interrupted connecting timbers and related "short timbering" is very traditional in a number of timber framing cultures (e.g. Old English, Germanic, Eastern European, Asian).

From a design perspective it is a tradeoff between perhaps not wanting to work with (or having) longer timbers. As such, if this is the case, the application of a great deal more joinery then become necessary. Inherently the strength necessary for a frames durability must be acquired in one of the two critical elements...be it longer members or more joinery.

Being a "modern project" you have the luxury of pulling from whatever traditions you please to achieve both your structural and aesthetic goals. If more joinery isn't an issue, then there are a number of design parameters that could be employed to achieve your goals without long timbers. Many modern designs, within the contemporary timber frame aesthetic, would support your interest in this design system. As is the case of a project we are currently on with 8 meter plus bent spans (~35' drip edge to drip edge) and 6 meter bays (~20'.) We had no real choice but to go with the "more joinery" approach and forgo an continuous connecting timbers for the length of the structure.

Good luck and we all look forward to reading more about your progress...


.


Edited by Jay White Cloud (07/02/16 10:40 AM)
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#33757 - 07/03/16 10:14 PM Re: Mid Span Beam Joinery Question(s) [Re: N_Butler]
N_Butler Offline
Member

Registered: 06/30/16
Posts: 6
Loc: Maine
Thanks all! It looks like I have plenty of reading and considering to do while I prep my stock. I may still default to a continuous plate given time constraints and not being able to wrap my head around how the interrupted plates can be joined successfully; it seems as though the interrupted plates would still see moment reactions at the posts and mid span similar to those of a continuous system, and that would be a lot to ask of the joints. I do appreciate the input and direction, I was really getting nowhere trying to research this through other means.

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#33758 - 07/04/16 09:18 AM Re: Mid Span Beam Joinery Question(s) [Re: N_Butler]
Jim Rogers Offline

Member

Registered: 03/14/02
Posts: 1605
Loc: Georgetown, MA, USA
One way to join interrupted plates would be with a spline. Here is a link to a view of a spline joint:

http://timberframehq.com/spline-joinery/

Jim Rogers
_________________________
Whatever you do, have fun doing it!

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#33759 - 07/04/16 10:07 AM Re: Mid Span Beam Joinery Question(s) [Re: N_Butler]
timberwrestler Offline
Member

Registered: 11/07/05
Posts: 268
Loc: Becket, MA
I just want to point out that you can indeed find long milled timbers, such as the 20 or 35 footers that Jay points out, at least in most places. And believe it or not, it's actually cheaper to hew out a 35' timber than it is to buy one.
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#33760 - 07/04/16 12:53 PM Re: Mid Span Beam Joinery Question(s) [Re: N_Butler]
TIMBEAL Online   content
Member

Registered: 12/10/07
Posts: 1875
Loc: Maine
Our next project, which is well under way, 40'x60' has 6-40'-10"x12" tie beams. The 60' plates are scarfed in the middle. A bunch of 24'6x6 joist lodged on top of the ties, covering 12'bays. I will do everything I can to avoid splices and excessive joinery. All white pine.

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