Embedded plate in region of concentrated reinforcement 2

[P205]

Are there any guidelines on how best to design embedded plates for steel beams located on a corner of a stairwell or elevator shaft that is acting as a shear wall and therefore contains concentrated reinforcement?

What should I be considering when looking at this situation? I feel like there is a lot going on in a small space (4-8 vertical bars, ties at 10" or 12", an embedded plate taking away cross-section, stud/strap anchors for the plate).

I know that I'll have to carefully consider the constructability of the area, making sure that strap anchors are offset vertically from the ties.

Any words of wisdom of caution? Best practices?

I've attached a picture in case my question isn't clear enough.

 

[KootK]

Embed plates with two columns of nelson studs is typically what I see for situations like this where you're not trying to couple shear walls or anything fancy like that. While some coordination between the embed and the zone cage seems like a great idea, my sense is that doesn't happen often and there doesn't seem to be any dire consequences. I imagine they just tweak the cage a bit to make the embed fit when the the outer face of the form work goes up. The main thing to consider here is congestion and it sounds as though you've got a fine handle on that.

 

[P205]

Thank KootK.

It's a fairly common item, yet of all the textbooks and resources I have, none of them discuss it (although, up until now, I've never had to design one).

 

[cliff234]

I lay out the bar configuration in the wall and adjust the embed plate to miss the bars. I space the headed studs at the same spacing as the shear wall chord bars or a multiple of the chord bar spacing (for me, that’s usually 6” chord bar spacing and 12” standard bar spacing). I design the embed plate using Hilti Profis and consider the eccentricity on the plate – and add at least 3” (6” is better) to account for misalignment in the field. These plates are notoriously mis-aligned. I usually find that I may need more than two columns of studs – or I space the columns of studs farther apart horizontally to better resist the eccentricity between the shear reaction and the centroid of the studs. I provide additional ductility reinforcing steel between each column and row of studs. These embed plates usually must be custom-designed. You can’t easily rely on a “one size fits all” embed plate schedule. Invariably there will always be beams framing right on the edge of the wall, or even hanging over the edge of the wall. Require the inspector measure the as-built locations of the plates and submit that info. Make sure that you have some “fat” in your design. It’s hard to field fix mis-aligned plates. Hope this helps. I’m probably missing a few things.

 

[TehMightyEngineer]

Another possible option that may or may not be feasible is to have the embed welded to the rebar. Eliminates both the conflicting studs and gets forces directly into the reinforcement where and how you want it. Possible mixing of trades though, and may not be feasible with your project.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)
American Concrete Industries

https://americanconcrete.com/

 

[Agent666]

If going onto the end of a wall I generally make the plate the same width of the wall even if it means adding a bit more plate. Eliminates any issue with getting the plate positioned out of tolerance across the wall thickness.

Also try to avoid placing them bridging locations where there would naturally be a horizontal construction joint, don't have half the plate and studs sticking out of the concrete as a poorly organised contractor won't plan to have the reinforcing in place to the top of the plate. If you have to do it then have some discussions with the contractor so they understand.

I did it once and got a call day after the bottom pour asking how the next set of wall stirrups were supposed to be slipped over the vertical bars with all the studs in the way. Ended up having to cut the plate and weld it back after the reinforcement was placed for the next lift.

 

[P205]

cliff234
I will take a look at Profis for this. I have it installed on my computer but never use it. At least not in a couple years. Thank you for your comments regarding constructability.

TehMightyEngineer
That's an interesting idea. I've seen before, someone welding long pieces of rebar near the top of the plate instead of studs. And then regular studs on the bottom end of the plate. I'll consider this approach.

Agent666
For the beam coming in at the end of a wall (beam parallel to wall), I have seen U-shaped plates where the plate is installed after the all is poured and the plate is through-bolted to the concrete. But maybe a plate the full width of the wall might be easier.

I'm not sure what you mean by "the bridging locations", but the rest of that paragraph makes sense. I will definitely consider the horizontal pour joints. I'd hate to have to cut the plate and weld it back on.

 

[Agent666]

Sorry I meant bridging the construction joint.

 

[Agent666]

SCI recently published a free design guide on cast in plates that may be of use. Based on UK practice though.

 

[P205]

Agent666
I took a quick look and this looks like a great resource, thank you. Even though it's based on UK practice, I'm sure I'll learn something new.

 

[KootK]

Great contribution with that guide Agent666. I regret that I have but one start to give you.

 

[TehMightyEngineer]

I got you covered KootK; added my star as well for that is indeed a fantastic reference.

Being on the other side of the pond I tend to not pay attention to the European resourced unless I stumble upon them. I really should browse their library more often, though.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)
American Concrete Industries

https://americanconcrete.com/