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Half wall used as guardrail

Half wall used as guardrail

(OP)
I am trying to figure out how to attach a 42" pony wall around the edge of an elevated floor and connect it to the floor in a way that it meets the 200 lb point load requirement in the IBC on guardrails. If I use 200 lb applied at 42" height, I get a moment at the base of 8400 in-lb. Using a 2x4 wall, if I try to just lag this wall down, I can't get the numbers to work at for any reasonable connection. Even assuming a put a strap or L-bracket on the outside faces of the wall, that only gives me 3.5" of moment arm for resisting the overturning, which means the restraint will have to be 2400 lb. How do these get built? Does anyone have any suggestions?

RE: Half wall used as guardrail

The 200 lb point load (or 50 lbs. per foot) can be spread out over a larger area than just one stud. The wall itself has out of plane stiffness that can be resisted by possibly up to an 84" width (42" downward at 45 degree splay each way).

That might help you get a connection that is workable.

RE: Half wall used as guardrail

A couple thoughts.

1. Can you balloon frame this section?

2. Here is an article for a deck handrail detail, which obviously isn't quite the same, but maybe you can modify the detail and get something similar. http://www.structuremag.org/article.aspx?articleid...

3. Can you design the top plate to span between supports at the ends and forget about bringing the load down to the base via the studs?

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

RE: Half wall used as guardrail

(OP)
One end of the wall is free, so I can't span between supports, and the floor is already framed so I can't have them balloon frame it. I have seen and often use that detail in the referenced article for decks, but part of this guard wall is going around a stair opening where the width can't be reduced, so I can't attach the wall to the side of the floor system, it has to be on top. I will try to take advantage of the 45° splay that JAE suggests and maybe I can find an L-bracket or something that will work. I thought that what I was doing was fairly common, so I am surprised that there isn't something more typical that someone could just say, "use these for that" but there doesn't seem to be anything that I can find.

Unless someone else knows something?

RE: Half wall used as guardrail

Shane:
Remember that the 200lbs concentrated, or the 50lbs/ft. can act in either direction on the top of the wall. The top plate on that wall has to be connected in such a way that it will distribute these loads to 3 or 4 studs. I don’t know if you can stretch that as far as 84" though. That is obviously a nasty condition, and you must be able to get down into the floor framing to make some moment connection.

Why not treat the 42" high wall like a shear wall, torsion box, box beam, whatever; with plywood glued and nailed both sides. The exterior skin laps down over the full height of the rim joist, but the rim joist needs special connection attention too. The inner skin stops at the floor sheathing, but is nailed to the top and bot. plates, which might be 2-2x’s or 4x’s. Then, every 32" or 48" (fl. jst. spacing) use a double 2x stud spaced to allow a post tensioning rod btwn. these studs. This rod gets attached to the fl. jst. with some hardware similar to that shown in the mag. article for handrail posts, but in this case in a vert. orientation. This starts to provide the moment connection btwn. the wall box beam and the fl. framing system. I would consider an outward failure as the critical condition, so place the rod off center toward the inside of the wall. The outer skin acts as the tension tie on an inward failure. Don’t over tighten the post tensioning rods, they will just tend to loosen due to creep and shrinkage in the wood framing, but they are there to counteract any tension forces when loads are applied at the top of the wall. Maybe use the hardware on the fl. jst. and on the double stud, only a foot above the bot. pl. to minimize creep and shrinkage effects. There are also spring loaded take-up devices to account for this shrinkage.

RE: Half wall used as guardrail

through bolt instead of lags

RE: Half wall used as guardrail

(OP)
Thanks for the responses. I ended up just having him use some MST27 straps onto double studs every 48" that go through the floor on the floor side and attach to blocking between the 18" deep floor joists. The outside is sheathed with plywood, so that takes care of that side pretty well.

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