Steel Knee Brace to stud wall
Steel Knee Brace to stud wall
(OP)
Hello, I have a situation with a steel knee brace coming into a wood stud wall. This is a residential balcony, I have no input on balcony design. Only being asked to size studs and advise on connections. My question is on the connection of the knee brace to the wall.
Ideally I'd like to sandwich a steel plate between studs with bolts,and come through the wall, but the architect would prefer to avoid penetrating the metal siding with the plate. The other option (see sketch) is to fasten a steel plate to the face of wall (outside OSB and standing seam siding) with lag screws into the stud wall.
My question is whether the second option is even workable. My first concern is that you have stand off distance between the steel plate and the stud, and NDS states the design values are for when "the connected members are in contact." Maybe this isn't a concern in reality, I would think the OSB would provide some bearing on the screw, and the siding is think gage material. But still, we don't have direct contact between the plate and stud. The second concern is screwing into the side grain of a stud, I'd probably require using a 6x6 post rather than (3)2x6 so there are no edge distance concerns. Lastly, it just doesn't feel right. The majority of my experience is with steel in industrial settings, so this is out of my normal range, but holding up a balcony with screws feels off (the KB load is only ~1300 lbs).
Appreciate any opinions or comments. I don't have much experience with wood, especially wood connections, so feel free to tell me I'm dumb and point me in the right direction.
Ideally I'd like to sandwich a steel plate between studs with bolts,and come through the wall, but the architect would prefer to avoid penetrating the metal siding with the plate. The other option (see sketch) is to fasten a steel plate to the face of wall (outside OSB and standing seam siding) with lag screws into the stud wall.
My question is whether the second option is even workable. My first concern is that you have stand off distance between the steel plate and the stud, and NDS states the design values are for when "the connected members are in contact." Maybe this isn't a concern in reality, I would think the OSB would provide some bearing on the screw, and the siding is think gage material. But still, we don't have direct contact between the plate and stud. The second concern is screwing into the side grain of a stud, I'd probably require using a 6x6 post rather than (3)2x6 so there are no edge distance concerns. Lastly, it just doesn't feel right. The majority of my experience is with steel in industrial settings, so this is out of my normal range, but holding up a balcony with screws feels off (the KB load is only ~1300 lbs).
Appreciate any opinions or comments. I don't have much experience with wood, especially wood connections, so feel free to tell me I'm dumb and point me in the right direction.






RE: Steel Knee Brace to stud wall
you will absolutely have to look at vertical support member and possibly double the stud if not add a column - but balcony loading will dictate that design
RE: Steel Knee Brace to stud wall
If the KB load is 1,300 lbs, the vertical component is about 925 lbs (assuming 45 deg.)
I would consider using 1/4x3" simpson SDS screws - 6 ought to do it.
You also have to worry about bending of the wood column and its attachments top and bottom.
Finally, the knee brace will pull the deck away from the house. Make sure you address this.
As a rule, I always cantilever things instead of kneebrace-ing them. Much easier
RE: Steel Knee Brace to stud wall
That may force you to run some anchoring beam between wall studs.
An articulated connection between plate and knee will eliminate moment and deformation of plate or poor welds introduced by inaccuracy in angles.
"Engineering is achieving function while avoiding failure." - Henry Petroski
RE: Steel Knee Brace to stud wall
My main concern is the stand off on the screws, and the idea of supporting a balcony with lag screws. But I'm not seeing any major red flags with the direction.