Shoring OSSJ with wood?

[JStructsteel]

Got some steel joists with a slab on top to shore while the wall is removed and beam installed. My plan was 4x4 under the top chord about 6-8" back from the support, and that be supported by a wood wall.
I dont want to goto bottom chord due to reversal of forces.

Anyone see an issue? Perhaps a bearing pad on the wood so the chord doesnt dig into it?

 

[XR250]

I think you need to post a sketch before you can get any meaningful help.

 

[phamENG]

I've designed something similar, but it was never used. As long as the load path is good and the members are strong enough, the material is...immaterial.

You have to be careful about how you're getting load out of the top chord since if you just put a block of wood under it the angles will knife through your block of wood. So make sure you consider alignments, stability of components, etc. A bit of a pain, really, but doable.

 

[JStructsteel]

I've designed something similar, but it was never used. As long as the load path is good and the members are strong enough, the material is...immaterial.

You have to be careful about how you're getting load out of the top chord since if you just put a block of wood under it the angles will knife through your block of wood. So make sure you consider alignments, stability of components, etc. A bit of a pain, really, but doable.

Yea, I figure if I am close to the bearing seat, within same distance from the first chord, I hopefully should be good on the joist. I will limit any live load during the shoring.

For stability, I was thinking a ledger type board on the side of the temporary wall, and they can attach the bottom of the joist to that, to keep it stable and not allow it to roll.

Short span, so load is not too much.

I will post my detail once its figured out

 

[KootK]

I think that you're better off shoring the bottom chord at a panel point. So long as you're reasonably close to the end, the potential for reversal should be trivial. For me, being able to shore the bottom chord simply, and concentrically with a truss node would outweigh any minor reversal potential.

 

[EngDM]

I think that you're better off shoring the bottom chord at a panel point. So long as you're reasonably close to the end, the potential for reversal should be trivial. For me, being able to shore the bottom chord simply, and concentrically with a truss node would outweigh any minor reversal potential.

A plus with this, especially for the double angle bottom chords, is you don't really have to worry about the angles digging into the wood as @phamENG mentioned above. Its probably much easier to just build these things the same length, concentric with the centerline of joist and not worry about any of the detailing to shore from the top chord.

 

[JStructsteel]

I think that you're better off shoring the bottom chord at a panel point. So long as you're reasonably close to the end, the potential for reversal should be trivial. For me, being able to shore the bottom chord simply, and concentrically with a truss node would outweigh any minor reversal potential.

My worry there is now the bars are in compression and buckling an issue. I know I can check these items. I know I can model up the truss to check, but was trying to avoid all that.

 

[KootK]

My worry there is now the bars are in compression and buckling an issue. I know I can check these items. I know I can model up the truss to check, but was trying to avoid all that.

Kind of depends on the situation at hand but, when I do this, I usually do it by inspection. I also usually specify that the shoring itself have x-bracing. That way the shoring itself can brace the bottom chord right where the stability demand would be the largest. After that, it's pretty much down to whether or not the last tension diagonal can handle the tiny amount of compression implied by the very short cantilever. Unless it's made of floss, it surely can. Heck, the top chord alone could probably just cantilever.

 

[Enable]

For this kind of situation I've generally used post shores at a convenient location beyond the wall, and installed blocking friction fitted b/w chords. Similar to Bones setup in this thread. If you require additional stability you could use frames or PERI MP props w/MRK frames.

EDIT - You'll need to give the workers some room to facilitate the demo + install. 8" may be enough or may not be depending on what they need to do and if they can access everything from the outside. If they don't need the interior space your idea of a wall is a good choice since it could also double as their hoarding for the demo area.

 

[KootK]

@Enable: it's a spiffy detail but, fundamentally, what makes it better / more stable than just putting in cross braced shoring at the location shown below?

 

[JStructsteel]

Kind of depends on the situation at hand but, when I do this, I usually do it by inspection. I also usually specify that the shoring itself have x-bracing. That way the shoring itself can brace the bottom chord right where the stability demand would be the largest. After that, it's pretty much down to whether or not the last tension diagonal can handle the tiny amount of compression implied by the very short cantilever. Unless it's made of floss, it surely can. Heck, the top chord alone could probably just cantilever.

What if the joist doenst have a vertical at the panel point? Just the "bar" bent and welded? Just resolve the forces?

EDIT-I see now, use wood to create a vertical member.

 

[KootK]

What if the joist doenst have a vertical at the panel point? Just the "bar" bent and welded? Just resolve the forces?

It doesn't need a vertical member. There should be a compression web hitting that same joint that came straight from the factory (literally) with enough compression capacity to get the job done.

 

[KootK]

I feel as though I'm getting gaslighted here or something...

 

[phamENG]

what makes it better

For the few I've done, space to work on the wall without knocking of the shoring and bringing the floor down on your head. @Enable probably has better reasons.

 

[KootK]

For the few I've done, space to work on the wall without knocking of the shoring and bringing the floor down on your head.

So just move the BC shoring in one more panel point.

 

[gte447f]

I agree with @KootK that shoring at the last bottom chord panel point should be fine in most cases for the reasons Koot has stated. Namely, the last compression diagonal is already a compression diagonal, and the last tension diagonal should be plenty strong enough in compression to handle the small amount of load reversal likely to result from shoring the bottom chord at this location. Directly shoring the bottom chord has the benefit of being simple and expedient.

However, I also really like @Enable 's blocking detail.