joist sistering question

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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.
Cheers, Wayne
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Wayne-
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.
cheers Bob
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franz fripplfrappl wrote:

Insufficient data- what problem are you trying to solve? Is joist damaged, is floor bouncy or sagging, are you planning to add a grand piano and a waterbed above, or what? What you are describing is gusseting, not sistering, and is usually only used on a damaged joist that would be a PITA to switch out or sister, which means setting another real joist right beside it, going all the way out to where the ends of the joist rest on the sill plate, crossbeams, or whatever.
Gusseting to stiffen a joist is usually done with metal plates, by the way, through-bolted through the joist. If the joist is sagging, you have to jack things back into square before you start. If it is just a bouncy floor, adding or replacing the 'X' braces between the joists may be all that is needed. Traditional cure for a too-long span is to add a beam at the midpoint, held up by screw columns, or grafted into the structure of the basement or lower-floor walls.
-- aem sends....
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Why are you wanting to "beef up" these joists? What you want to accomplish drives the retrofit design.
cheers Bob
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