Thanks for the responses.
I may try later today to post a picture or two to help further explain my questions.
I do use ‘deep’ braces were I can, we use 4’ and 5’ braces often. It’s not uncommon for our braces to enter the head room and go below head room at times. I’ve contemplated using 6” or 7” wide brace material in certain locations to gain additional tenon capacity. I’ve thought about ‘fat’ tenons, double brace tenons, using oak braces in pine frames and I’ve thought about using steel. There I said it ‘steel’, such a dirty word! I’d like to think I can design a ‘traditional’ timber frame using ‘traditional’ bracing. I’m not against using a lot of bracing, we do, but I’ve stopped short of using ‘non-traditional’ bracing.
I’ve seen a few buildings in the NE that have used large post to sill braces. I’ve heard those braces referred to as ‘tension’ braces. These ‘tension braces’ are only on the exterior of the building, gable walls, etc. I like the idea of stiffening a gable wall when practical by use of sheathing and additional bracing, but it’s the interior bends that are problematic. Let’s say you have a 48’ long building w/ 12’ bend spacing. The gable walls only see 6’ of wind load while the interior bends see 12’ of wind load. That’s my definition of a free standing TF. Those interior bends do not benefit from the gable walls additional shear capacity and must carry their full 12’ share of the wind load acting as a ‘standalone frame’. That appears to be the most common approach to evaluating TF’s for wind load. It is this approach that generates high tensile loads in braces for many TF’s, small or large. This is the area were I’m struggling. I’d like to get a sense on how other timber framers and engineers approach this problem.
EH
“I am not certain if there are any studies on this. I saw some studies done on pegs but not tenons.” I agree that most of the research appears to be directed toward ‘pegs’. My reading indicates that there many studies that evaluate the failure mechanism in mortise and tenon joints and timber frames as a ‘whole’. I believe most of the studies indicate that many mortise and tenon joint failures are relish related as opposed to peg related. Further, when evaluating a single story or two story frame, Dick Schmidt’s work, most frames start to fail do to tensile loading of braces, actually relish failure of the brace tenons and/or brace pegs.
In closing, my conclusions to date follow.
For lateral loading (wind) brace tension is many times the major failure mechanism for timber frames and brace tension is potentially the most difficult aspect for standalone timber frame design, it is for me. I’m trying to understand how best to accommodate brace tension loading in my designs.
Thanks again for the responses.
pete
