Steel Embed Plate in Concrete - Simple shear Connections

[Guastavino]

Without much published literature (that I can find), I'm curious what other folks use for embed plates with headed studs in cast-in-place concrete walls to support steel beams and girders.

I'm curious on stud sizes, plate thicknesses, and also what kind of shear connection do you use?

I'm using Hilti profis (and my spreadsheets) to create a typical detail for an upcoming composite steel job with concrete walls around the perimeter. But I'd like to see what others are doing to maximize my economy. I'm leaning towards a standard plate thickness of 3/4" with 3/4"x6" headed studs. Then adjust the width and depth for various beam sizes. (As an aside, I just tried to help a contractor by giving different bolt sizes for a wood job...and well, you can imagine they accidently put them in the wrong places...so I don't want to spec a bunch of different stud sizes and plate thicknesses).

The company I used to work for did a lot with double angle connections, but that of course drives the embed plate size wider. I like double angles, but they can be expensive and I'm curious what you all have seen work well in the field. I don't want to stay in my double angle rut.

Thanks!

 

[mike20793]

I've used them extensively. The plate thickness depends on the load and the size of the beam. I always include a little extra setback on the beam and some wiggle room for locating the plate. Usually thicknesses are around 3/4 inch with 5/8 or 3/4 diameter studs. I always assumed it's going to be a shear plate connection, at least that's what I show in my detail and it's what I always recall seeing them use in the field.

 

[KootK]

-1/2" plate for little stuff. 3/4" for big.
-3/4" studs 6" long unless there's a spatial reason to go four.
-I usually put the studs 1.5" to 2.0" in from the edges and keep the spacing between studs down to around 6".
-I like double angle or single angle for simple shear because I feel that it reduces the chances of an accidental beam/concrete moment connection that would doom your average embed plate.
-If I've got axial loads coming in from the beam, I like a flexible seat angle welded below the beam and to it and a single angle on the web for stability. Again, less accidental moment transfer.
-If I intend to deal with some moment or serious eccentricity at a joint, I'll often use deformed bar anchors at the top row instead of studs. Kinda depends how much space I have to play with.
-I'll generally assume 3" of misplacement in any direction in the design and detailing of the plate. Nothing cost more than rework due to a botched install.
-Try to keep the weight of large embed under two hundred pounds so that, hopefully, they won't have to be craned into place. It can be surprising how quickly the weight adds up.
-I've had issues in the past where thermal stresses from angle/plate welding have caused concrete cracking and even stud shearing in long embeds. This is another good reason to sometimes use multiple smaller plates as opposed to large single plates.

I generally don't sweat the cost of embeds much. I believe that their material and fabrication cost is low relative to the cost of shipping, installation and, in particular, rework due to positioning errors.





I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Guastavino]

Thanks mike and KookK. I have read (and it makes sense) that the thicker steel plates help with the spalling of concrete, but it all really depends on welding technique, etc.

I may post my typical detail at the end and see what comments folks have.

@mike, on the shear plate connections, I'm assuming you have the shear plate shop connected to the beam and then they field weld it to the embeds on-site? If so, is there any field adjustment tolerances?

Thanks!

 

[KootK]

I'm assuming you have the shear plate shop connected to the beam and then they field weld it to the embeds on-site? If so, is there any field adjustment tolerances?

The version of this that I'm used to goes something like this:

1) Cast embed plate.
2) Weld on shear plate or single angle with long slotted holes for field tolerance.
3) Bolt beam into place.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Teguci]

PCI Design Handbook - Chapter 6 "Connectio Design" has a wealth of info and examples for the design of embedded plates in concrete using Deformed Bar Anchors and Headed Concrete Anchors. Minimum plate thickness is limited to 1/2 x anchor diameter.

There is also a note on keeping the surrounding concrete from spalling when welding. In short, minimize the weld size, use multiple passes, use stitch welding, and pretty much anything else to keep the weld heat down. If you can provide a gap between the concrete and steel plate around the edges (thick elastic band or sim), that will also help prevent unsightly spalling.

If you have tolerance, threaded inserts can eliminate field welding and still get a decent capacity.

 

[Guastavino]

^Thanks. I will have to purchase that. My PCI is an older copy and I haven't bought a newer one since going out on my own.