Timber Knee brace for up to 2 kips axial

[Everroux]

I am trying to design the connections of the 4x6 knee braces inside of a 5.5x5.5 column and 5.5 wide beam. I would like to use screws that do not require pre-drill. However, with the brace in compression, how do I account for the lateral resistance of the dowels that actually go through the end grain of the knee brace?

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1624458827/tips/Untitled_j7ij1q.pdf[/url]

 

[1503-44]

I dont think you're going to get 1500# shear out of two screws, not even thinking about end grains.
I'd also think that predrilling is necessary for whatever is the diameter of the bolts you should be using.

I think I'd be looking at some steel strap or plate connection detail,

 

[STrctPono]

In my design and construction experience, you want to through bolt those connections, not use lag screws. I find that it provides a much stiffer connection and will not loosen over time like a screw might. Even if you used screws, you should certainly be using something larger than a 3/8" lag screw, which would require predrilling. I would also move the one fastener closer to the acute cut end.

 

[dhengr]

Everroux:
The structural screws won’t do much more than hold the knee brace in place with no loading. You have three options. (1.) Use a split ring or shear pl. dapped into the ends of the knee brace and into the col. and beam, with a lag screw which fits them. (2.) Cut the knee brace square, and full length from tip to tip. Lay out the sides, at the ends, like you show on your sketch. Then cut the four 45° triangular tendon shoulders on the end of the knee brace; a 2” shoulder, a 1.5” thick tendon, and a 2” shoulder, for a total of 5.5” member width. Cut the tendon cheeks, and clean up the cheeks and shoulders. Get a real carpenter to do this, not some chain saw and hatchet jockey. Lay out and cut matching mortises in the col. and the beam. (3.) At the ends of the knee brace, make a square cross-cut which leaves a 1” end grain butt. This will shorten your sketched knee brace by 2” in length. Then, cut a matching 1” deep notch across the beam and the col. to fit the end of the knee brace. Again, have a real carpenter do this so they actually fit nicely. He may have to relearn to use a hand saw and a sharp chisel which he will probably have to bring with him, because you probably won’t find them on most work sites these days. All of this joinery should fit snuggly, not be a cobbled mess. On the latter two options a couple, predrilled structural screws will do the trick for attachment. You must pay some attention to what the notches and tendons do to your beams and cols., you have to design these members and joints by hand.