I am about to start a new frame with white oak 3x7.5 braces. The braces on outside walls will be pushed to the outside 1.5" tenon, 1.5" shoulder. For the interior, however, I am thinking of putting them on center. When a brace is housed on the center of a post is it common to put a 3/4" shoulder on each side of a central tenon or cut them exactly as the outside wall braces? Also, I have read old barn frames often have no pegs since the builders understood bracing in pairs put them in compression. If this is so, why peg them today? What function does a brace peg serve? Thanks

Hello Jerod:
Here is my opinion on the cutting of braces and shouldering. These views are from what I have observed in many old structures.
Braces are usually set in line with the tenon of the girt\beam or post, to be able to withstand heavy side thrusts without twisting the post or girt.
(90% of the time the tenon is offset to one side of the girt or post no matter where it is placed in the framework, so the tenon on the brace is also ofset to one side, and placed in line.
I really only seen braces placed centrally in Dutch barns with the large anchor beams. In these case the braces were placed in boxed seatings in the centre of the anchor beams, and where it met the post. I suspect the tenon had a shoulder on both sides of the tenon, but can't verify this.

Dear Jerod,

This is an excellent question and one to which I have given some thought over the years.

Braces without pegs:-

I bet that these are all made from quite small section probably 3" x 4" and made from a good hardwood (typical Ohio barn - Rudy Christian please comment). These braces simply don't have a lot of room on the tenon to drill peg holes and still leave sufficient end relish on their tenons to make pegging a practical consideration. Thus brace number will be increased, probably to every available position along the length of a building. Braces of this size would not be appropriate on cross frames much over 8ft wide and also setting braces this size back into a housed mortise would further reduce the available tenon length and thus the reasons for non pegging become more apparent.

Bare faced tenons :-

Provided the brace stock material is of good straight and fairly thin section then an offset tenon is the quick and easy answer. If the brace stock material is twisted or of non uniform cross section then it is better to work from centre lines snapped on the timbers and hence a centrally mounted tenon might be more practical to layout and cut but the distance between the tenon and frame outside face needs to be kept about the same width as the tenon so fair facing of frame members will not necessarily be achieved and hence a move towards offset or centrally mounted braces is precipitated.

Centrally mounted tenons :-

Generally as previously advised this is the approach taken on big section material where offset tenons could allow for a gap opening up on the side of beam /post furthest from the tenon due to offset draw bore forces as the joint is pulled up.

Pilton barn has centrally mounted tenons cut into 10" wide cruck blades (see UK today).

Deep Section Braces :-

Braces which are 8" and deeper tend to be employed when two pegs are to be used per tenon. In England the braces on medieval buildings are often curved and are about 8 - 9" deep. This provides a even greater ammount of effective tenon width inside the mortice to help resist relish failure and help reduce joint/peg stress levels or even still resist pull out if a relish crack opens up in a tenon at a peg location. The peg diameter can also be reduced which in turn marginally improves the tenon performance against relish failures.

Rules of Thumb :-

Use bare faced tenons on material up to 4" thick in 1.25" / 1.25" (2.5" hardwood) or 1.5"/1.5" (3" hardwood) or 2"/2" (4" softwood). Beyond this thickness consider using offset or centrally mounted tenons in for example combinations of 1.25/1.25/1.5 (4.5" hardwood) or 1.5"/1.5"/3" (6" hardwood) or 2/2/2 (6" softwood) or 2/2/4 (8" softwood), etc.

I hope that your question will inspire many further thoughts and revelations.

Regards

Ken Hume

Thank you for your comments. A question about the brace mortice: I have been looking through a book by Jack Sobon in which he cuts the brace mortice to 90 degrees at both ends (no 45 degree to match incoming brace). Intuitively I imagine a brace in compression wanting to thrust inward with only a corner and pegs to stop it. But even with a 45 the movement of the wood or poor workmanship may also leave a gap, hence the same situation. I am wondering if it is common to cut a 45 or 90 on a brace mortice and what areas of contact are critical? Also on 8" deep braces would two 3/4" or 7/8" pegs be preferrable to one 1" peg. Ken Hume, I refer to your comment about smaller pegs resisting relish failure marginally better and two pegged braces. Thanks

Dear Jerod,

There should be no contact between the back of the brace and its housing whether cut at 45 or 90.

When using deep braces like yours in compression the braces will deform inwards and outwards along the thinest section axis and will not push against the back face.

Generally when a long mortice slot is cut this would be provided with a tapered rear housing face.

Small depth braces can be fitted to 90 degree mortice because it is more difficult and quite time consuming to cut a sloping shoulder into a very confined mortice bottom.

To answer your question about peg numbers to be employed would really require that we have a better understanding of your frame layout and also be able to run some numbers on the analysis programme to see just how heavily loaded the braces are in tension.

Using 2 pegs will move the brace from operating in a simple "pin" connection mode to "moment" connection mode and this will improve the frame stiffness.

You are hopefully now beginning to realise why the services of timber frame engineers are sought on larger non standard type frames where getting this kind of thing right matters more than on a building the size of a typical Jack Sobon style garden shed.

Regards

Ken Hume

For simplicity, I'll refer only to the mortise in the post, alhough the same would be true in the beam. Yes, the thrust from the brace is directed along the brace, at 45 degrees. Thus, there are 2 surfaces that bear the load. The bottom of the mortise is one of these critical bearing surfaces, the other is where the shoulder of the tennon contacts the post. You would be correct about the back of the mortise if there were no shoulder. CB.

This discussion brings up a question which I have pondered over in my mind on several occassions. What does a structural analysis (FEA) look like with braces double pegged at each end. Intuition tells me this eliminates the "hinge" action that can result at the peg now (I think that one is obvious) and it seems that the destructive nature that braces transmit to the post/beam connection could potentially be minimized by having the increased rigidity of the brace connection taking more of whatever load is being put on the frame. I understand double-pegging on most frames as they are designed causes other issues such as the need to increase brace tenon size, etc. in order to accomodate the additional peg, but if you design to accomodate that (larger tenon, smaller dia. pegs), are there any other reasons that a double pegged brace would not be an advantage. Yes, I understand that in extremely severe conditions (i.e., earthquake, tornado, etc), a "hinged" frame could possibly survive better than a fully rigid frame, but it seems that under more normal conditions, a more rigid frame could better eliminate frame movement and the bad things that go along with it. I am very interested if anyone has modeled this quantitatively or has some real world experience. Great discussion so far......hope I didn't ruin it!

I have to jump in here again. It seems to me that you are making this question of pinning braces too complicated. All you have to do is copy what has been done over many hundreds of years. Many buildings that I have looked at and examined never had any pegs, and are still standing true and straight, and this after 200 years of high winds, tornados, earthquakes etc. I am not saying that it is never done, but in this area you may only find one building out of 50 that has pinned braces, and it is considered an oddity. Putting oversized braces in just to accomodate pinning in my opinion is overkill, and not necessary, or would have been done by the true and experienced timberframers of days gone by, and that would have come about from improvements over the decades due to failure in the bracing. Pinning the braces will not be sufficient to hold a frame rigid, it will eventually work alittle in the winds which is a normal movement. food for thought

Hi Northern Hewer,

The timber frame houses and barns in my neighborhood in Hampshire, England range from about 1750 back to the 1300's and the vast majority that are fitted with curved main, wall and roof braces have two pegs. I have observed some larger buildings with 3 lower and two upper pegs on cross frame bracing !

Towards the end of the medieval period (say late 1500) there was a move towards employing straight stock braces and these are generally fitted with one peg only and tend to be less deep in section (6" or so).

These buildings have stood the test of time compared with the buildings that you describe which relatively speaking would appear to be still in the flush of youth.

I assume that where advice and guidance is being given to relative newcomers it is important for us to quantify and / or qualify advice explaining the circumstances in which this practice might be acceptable.

In my earlier note above I tried to rationalise where or why non pegged braces might be found. I would be interested to discover whether my reasoning holds true. Could you please explain further about buildings that are fitted with non pegged braces.

What size are the braces that you have seen without any pegs ?

What type of building - barn / house ?

Regards

Ken Hume

Regards

Ken Hume

Hello Ken:
I thought that I would get a response and I appreciate your comments. Our area here will never catch up historically to your very old buildings age wise, but then again how far back do we go for good advice, and how many years should a building stand to say one construction method is better than the other. It sure all boils down to keeping the roof water proof for all those centuries, rather than how many pins are in the braces.
My advice to a novice beginner still stands, and I repeat that the late 18th century barns, houses, school houses, drivesheds, shops, and yes even smokehouses that still survive in this area the majority do not have pins in any of their braces, and as long as the foundations are firm, and the roofs have been maintained they are yet standing true and straight. I have run across 2 barns in all my time that had one pin in either end of the braces, and the braces were vertical sawn 4" by 4" in cross section. Even in the oldest barn that I viewed, which by the way had all hand hewn-- timbers,-- 4" by 4" studs--and 4" by 4" braces there was no pinning evident. Now taking this alittle further these people came from Germany 300 years ago, and I find it hard to believe that pinning braces would all of a sudden be dropped when they arrived here in Upper Canada--what do you think?