The Simspson SDS 1/4 x 2 seem like a good choice. BTW, the holes for the screws need to be a hair over 1/4", I had some holes punched at
1/4" exactly and had to ream them out a little to allow the screws to pass easily.
So the screws are there are to transfer the shear load to allow unitary action and then as you say to keep the plate from buckling out of plane. How does one design the fastener pattern for each of these purposes? Obviously for the buckling, the plate thickness is important. So the fastener pattern will determine the answer to another question raised, what is the minimum plate thickness?
Looks good to me: E_steel / E_oak is about 18, and 2" / (1/4") = 8, so a full height steel side member is 2.25 times as stiff.
I've done this sort of thing in various forms of the years.
And the question always comes up "how thin can we go?"
Well, thinner is cheaper but at a certain point it would not be much better than paint.
I have a machine shop buddy as well & he keeps the "aerospace engineer" in check. He may not be able to "run the numbers" but I've never seen anything he's built fail & nothing he build is wasteful of material. Working together we've come up with some really cool, cheap & workable designs. I guess in 30+ years working metal he learned some stuff. :) And his limit for this sort of thing is 1/4"
I could give a long winded (typical, I guess) answer about thickness but the short answer is:
I'm ok with 1/4" but thinner (3/16 or less) makes me nervous.
Long answer:
The 1/4" added to a single side more than doubles the joist stifness, so thicker really isn't needed. Thinner runs the risk of the plate not acting as a unit with the joist>>>>>>that means more screws.
The out of plane (sideways) buckling of the system is driven by the oak joist. The joist in the weak sideways direction is ~30x stiffer than the steel plate. That's why we need to screw the plate to the joist. If we went thinner the sheet would be even more likely buckle & curve away for the joist. it would have very little sideways stiffness of its own (~40% of the 1/4" plate) so you'd need more screws
How many more, I'm not sure (I'd swag it at ~2x) & I'm really not sure how to calc it.......time for a lunch with some of my former students to get their input. :)
Going from 1/4 to 3/16 saves ~25% material cost but IMO drives the risk of the retrofit not working, way up.
BTW the span on these joists is ~16', what is the spacing?
The reason for this question is......are you sure the bounce is coming from the joists? If the joists are more than 16"oc the subfloor could be the problem.
IMO 1/4" is still real "plate" material......3/16 drops into the category of sheet.
Steve, Wayne is correct about oversizing the hole for the SDS. I'd go only about .010 but check the proposed hole size with some screws.
You've got a couple of things going on depending on how the plate isadded & whether is bears on the joist support.
Like I said in my post to Steve, I'm really not sure how I'd calc the screw pattern but two rows 12"oc staggered seemed reasonable for 1/4" plate. Since the plate is full depth we're not making a "composite" beam like a T-beam or other assymetric shape, the fastener schedule need not be as dense as for those types of apps.
So I'm thinking all we need to consdier is the overall load path. Load goes into the "joist & steel plate system" over the entire span. If the plate doesn't bear on the joist support (wall top plate?) then we need to take the collected load out of the plate & back into the joist at the end of the plate. And this would require a heavy screw pattern If it does bear, we need to provide a bearing plate so that side plate doesn't cut into the top plate.
Here's where I really like to bounce this concept of someone who can poke holes in my ideas. I'm not totally sure what the screws pattern needs to look like near the ends IF the steel plate doesn't bear on the joist support. If it does, I pretty sure that the 2 rows- 12"oc staggered is fine.
What I'm say is that if the steel side plate completely mimics the joist then the screw pattern is less important. If side plate doesn't span & bear as the joist does....then the screw pattern is more critical.
Ya, they're 16" OC , give or take an inch. . You know in 1877 i rekon they only could measure with their forearms or something. It's funny, the vertical studs run from 13" to 19" spacaing. you'd think they could have cut a stick or something and at least made them all the same.
thanks for all your input.
s
BTW the span on these joists is ~16', what is the spacing?
The reason for this question is......are you sure the bounce is coming from the joists? If the joists are more than 16"oc the subfloor could be the problem.
IMO 1/4" is still real "plate" material......3/16 drops into the category of sheet.
Steve, Wayne is correct about oversizing the hole for the SDS. I'd go only about .010 but check the proposed hole size with some screws.
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