I was hoping someone could point me in the right direction in how to get some specific info on the strength of scarf joints. The material I've read is quite good at diagraming them, discussing layout, and some what on placement but they don't specify strength. For instance how much is the strenth in bending reduced, 60%, 80%, 90% of original strength. Is there a rule of thumb I can follow? I realize different scarfs have differenet characteristics but is there a way to quantify these differences? Any help or suggestion on where to look for more info would be greatly appreciated.

Hi
There was quite interesting discussion about scarf joints position recently and I suggest you to read it first. Everyone was giving his 2 cents but the conclusion was not clear at all. Some vote for scarf over post, other like it over brace. I'd say it is more like historical versus engineering perspective controversy.

So, your question was about scarf bending strength and you probably wonder why I talk about location?
From the engineering point of view, scarf should be located as close to place with zero bending moment as possible. In other words it means scarf has no bending strength. Well, there certainly is some capacity in bending which can be calculated. However, it is not considered either a "good" nor "safe practice" to do so. Unless you orient your scarf vertically indeed. It is probably not the preferred "old fashion way" and also involves bolts & nuts & washers (& shear rings) rather than wooden pegs.

As for the placement I suggest to run structural analysis first and than decide where you need to locate your scarf. Because you may not necessary need negative moment over post and thus you may use direct structural support provided by post and have braces handle only lateral loads as they are supposed to.
Very few people actually house braces so the only structural member in play is one peg each side (hypothetically tenon to mortise edge after peg cracks and some imaginary friction between brace and beam/post). Not much, it is barely enough for bracing and takes just one crack to ruin it all. If you are still tempting to place your scarf joint over brace, let me suggest housing the brace on both sides.

Hope this helps
Michal
TFDesign

Michal, In square rule timberframing it is common practice to house the braces. I have dismantled several old frames were the braces were not pegged at all. I have also raised new frames were we did not peg the braces. braces are designed to work in opposing pairs in compression. This photo was taken at a TF Guild rendezvou in 2003. The braces were not pegged. Tom

Hi Tom

Thanks for the picture, I like this one.

I'm sure I said there is a few not none who house the braces. Maybe I was wrong and all of you house braces. It was just my personal experience.

You made some comments about how brace act, sure you're right and I'm pretty aware of that. I also agree that properly housed brace does not have to be pegged. But I was always concerned about accuracy and squaring frame where you need to have some allowance for movement. That's why gap at shoulder face may open after you square the frame and pegging is a simple fix to keep brace in place.

As of the engineering concept for brace in compression I would always assume the following

housed & pegged brace:

• possible gap between surfaces
• peg is the only structural element
• peg breaks
• surfaces are closed
• load is transfered through shoulders

housed brace only:

• possible gap between surfaces
• free movement until surfaces close
• surfaces are closed
• load is transfered through shoulders

and what about braces in tension?

housed & pegged brace:

• possible gap between surfaces (has no effect)
• peg is the only structural element
• tenon breaks (not enough end distance)
• surfaces are widely opened
• no tension resistance whatsoever but brace can be kept in place by peg & tenon relics & possibly by shoulder shape

housed brace only:

• possible gap between surfaces (has no effect)
• surfaces are widely opened
• no tension resistance whatsoever, brace is possibly kept in place by shoulder shape

Your preferences may be different but this is why I prefer pegged braces.
Michal
TFDesign

I have always been taught that braces have no strength in tension. Having repaired hundreds of relished brace tenons, I have to conclude that this is the safe assumption. Like you said, one crack, and you loose it all. Pegging braces is great for keeping things where they belong during assembly. I do not think that pegging the braces allows for shrinkage in the post between them, and I would be disinclined to draw bore braces.

Tstarmer, Your questions about scarfs are good ones. More reason to push for testing of scarf joints. Tom

Would it make sense to draw bore so that the brace is pulled down the post but not into it?

A gap at the nose of the brace can filled (wedged) to keep compression forces from acting only on the peg.

When I have draw bored braces, it has always been in line with the brace, a little in and a little down. Be sure there is plenty of tenon beyond the peg to avoid relish. I have seen a lot of wedged braces in old barn frames. Tom

On braces, collars, struts, etc. it is best to draw in the direction of the grain of the tenoned member. (as Tom is saying)

If you draw across the grain of the tenon, the peg will almost always split the tenon.

Gabel