Concrete Column with Embed Plates
Concrete Column with Embed Plates
(OP)

So I've been studying ACI 318-08 App D all day on this particular situation. No examples to be found as I search and search for a concrete column with embed plates. As I understand I need to check Vcbg, but I get to multiply by 2 (Per D6.2.1(c)) since the only load is the 120k Shear load (LRFD level) is parallel to the nearest edge. That yields only about 30ish kips of allowable load for quite a robust embed plate. Now, I can of course use the D6.2.9 anchor reinforcement, but I can't really fathom what the failure plane would be for a column embed like this, thus I don't know what rebar to develop.
To me Vcbg doesn't make sense for a column like this. Pryout check makes sense (but even then stirrups help prevent that), and when I check that I get 127.5 kips of capacity.
Anyone encountered this before and have thoughts?






RE: Concrete Column with Embed Plates
The plate doesn't really do a lot for you in that situation. (Except for the uplift load.)
RE: Concrete Column with Embed Plates
RE: Concrete Column with Embed Plates
Ok, that helps. I thought we were talking about the shear load from the HSS.
For that stud group, I don't know if the spacing is large enough to preclude a group failure, but on a stud by stud basis, to quote sect D.6.2.1 (which you mentioned):
"For shear force parallel to an edge, Vcb or Vcbg
shall be permitted to be twice the value of the shear
force determined from Eq. (D-30) or (D-31), respectively,
with the shear force assumed to act perpendicular
to the edge and with ψed,V taken equal to 1.0."
Essentially twice the load cap. as if it was acting perpendicular to the edge. If the spacing of the studs is 3 times the edge distance.....group effects would not be involved.
RE: Concrete Column with Embed Plates
As an aside, I'm not convinced that Vcbg calculation would accurately predict anything for this application...but it is the code!
RE: Concrete Column with Embed Plates
As far as the re-bar goes.....you could treat it like shear reinforcing (in Appendix D): anchor the re-bar in the failure zone and develop it beyond that. The interesting question with that would be the development length to use......compression or tension? I would think compression....but not sure.
RE: Concrete Column with Embed Plates
In the days prior to Appendix D I’ve seen sections of beefy W14’s & W12’s cast into the concrete with just the face exposed. The beams and a stiffener seat were both field welded to it. I don't know if that would overly interfere with your column reinforcing in your situation but it’s just another potential avenue to explore.
RE: Concrete Column with Embed Plates
I may just drop the steel column down and connect the beam to the column, then just fill the top of the pier/corner retaining wall with concrete and be done with it. Makes the concrete placement at the top more difficult, but is a better connection I would think
RE: Concrete Column with Embed Plates
To me, it would look something like Fig. RD.6.2.1(c) or (d) [second pic]. I would think if you have anchorage in those (shaded) zones you would be ok.
RE: Concrete Column with Embed Plates
RE: Concrete Column with Embed Plates
I would think (from the centerline of the anchor) 1.5 * the edge distance.
RE: Concrete Column with Embed Plates
This assumes a 2 1/2" eccentricity from the 120 kip vertical shear load from the bolts back to the column face and assuming f'c = 5000 psi for the concrete.
The distance from the top headed studs to that construction joint was included - only perhaps 3" or less?
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RE: Concrete Column with Embed Plates
Ultimately there is no way to make numbers figure for the column without 6.2.9 anchor reinforcing. The question is where is the failure plane. I don’t know...see below for my thoughts but again I think app d falls short on this
RE: Concrete Column with Embed Plates
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RE: Concrete Column with Embed Plates
Obviously, you'd be limited by how much the bar develops in each "failure zone". The force in the bar would be cumulative, and you would develop it fully once the studs end. Capacity would be X number of studs * the afore mentioned capacity.
I like JAE's latest suggestion about putting the beam over the column.
RE: Concrete Column with Embed Plates
Tension breakout and shear pryout would be likely failure mechanism which I would think would create a failure plane that returns to the same face of the column as the emebed (yellow line). There is likely going to be some incidental moment created by the construction tolerances allowed. I would make sure to spec a slotted connection for at least one end of this beam as well, got bit on a job with an embed where beam was installed in summer building was still open in the winter and the shrinkage failed the embed.
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RE: Concrete Column with Embed Plates
I'd also point out there is a tension on the central row of studs in carrying the eccentricity moment from the simply supported beam. because your beam cleat is central, all of the tension load goes into the central row.
On the assumption of the plate being relatively stiff in plane each row of studs could be assumed to take ~1/3 of the shear, with the outer rows only taking shear, and the central row taking an elastic distribution of tension force (higher tension on top studs, compression at base of the web/fin plate)+ approximately 1/3 of the shear.
As you are no doubt finding the concrete breakout strength won't give you a lot of capacity especially when close to the edge, you might need to justify additional shear stirrups/ties in the column with a strut and tie, or redistirbute studs to have more edge distance to engage more concrete and/or to anchor stirrups past the failure plane which I believe is/was allowed in appendix D.
RE: Concrete Column with Embed Plates
To the issue of scale, I did the embed shown below this morning. Similar proportions, infinite side cover (wall), and lots of eccentricities. 35K capacity; maybe 60K with the misalignment eccentricity removed. The real plate has another row of anchors making the layout symmetrical. Interestingly, capacity is higher with those anchors ignored as the the most demanding local stud failures are not considered. I'm sitting on the fence regarding the validity of the design check but that's a subject or another post of my own.
Your supplementary reinforcing here, for pryout, would be your column ties I think. That said, I'm not sure that we're allowed to use supplementary reinforcement to address pryout.
I still wouldn't count the slab as part of your breakout concrete. You'd have to move the breakout frustum in the column a fair bit before engaging the slab I suspect.
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RE: Concrete Column with Embed Plates
Right. My sketch was based on the studs being "far" from each other (to get more capacity). If it's close enough to where the zones overlap....it will get more like Celt83's sketch.
RE: Concrete Column with Embed Plates
RE: Concrete Column with Embed Plates
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RE: Concrete Column with Embed Plates
I have this “condition” in several locations but much lower loads, more like 60 kips. I am inclined to either extend the beam to bear directly on the column, or just frame the beam into the column. I lean towards framing into the column to simplify the connection...
RE: Concrete Column with Embed Plates