Corner angle embed plate capacity

[xp1]

Hello,

I'm an intern trying to determine the capacity of the angle shown in the attachment but I'm having trouble figuring out how to do so. PROFIS or other software that I know of don't have such embeds in their inventory so we thought of figuring out an analogous shape. The attachment shows our thinking: I think the failure plane would be like that based off ACI, and so I could maybe use a square plate with a width equal to the width of the failure plane and the embed depth shown. However I don't know what edge distance I would use.

Would anybody be able to help me validate my method or show me another way of doing this? Thank you.

 

[KootK]

I avoid using that arrangement for serious loads, despite its ubiquity, precisely because I don't know of an accepted method for evaluating its capacity.

I have to say, however, that your proposal actually sounds like a pretty reasonable lower bound capacity method. It's clever. The concrete checks will have to include shear, tension, and moment on your hypothetical failure plane however. I don't have high hopes for the capacity.

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.

 

[xp1]

Thanks for the response, I'll inform the engineer behind the idea. We don't have high hopes for the capacity either, but it's only a stair landing support so the demand isn't too high.

Follow-up question: do you think my drawing is an accurate representation of the internal shear and tension? I'm not sure where the moment would come from though

 

[TXStructural]

I think the failure would take the shortest path, which looks like it might be from the bottom the head to the end of the leg on the angle. Your breakage will obviously be a cone around the anchors. I would count only on tension across the smallest failure plane, and I would avoid this detail for anything structural since it is not ductile. Where this is used, it may be initially compromised because the steel does not shrink with the concrete and the restraint causes some cracking. A better detail would use one or two DBAs that develop into the floor. This assures that once cracking occurs, there is sufficient strength to avoid a brittle failure of the support.

As far as getting a number, ACI 318-14 chapter 17 does include cast-in-place anchors. You should be able to apply the method for an edge directly since the angle does not change the tension characteristics of the concrete. Obviously you would use the distance to the edge of concrete where is is formed by the angle.

 

[KootK]

Follow-up question: do you think my drawing is an accurate representation of the internal shear and tension? I'm not sure where the moment would come from though

I do think it an accurate representation. If I were doing this, I would assume that:

a) all of the vertical load is applied at the angle end of the studs and;
b) there is no concrete between the angle and your blue failure plane.

If you look at it this way, I think that you'll see the moment on the stud and the concrete breakout cone. Is this a conservative assumption? You bet -- that ignored concrete will help. However, without considering this moment in some fashion, I feel that your proposal fails to take into account a prying action that I will be present on the concrete breakout cone.

Have you checked the PCI manual for guidance on this? I don't know if they have anything but, if anybody does, I suspect it would be PCI.

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.

 

[xp1]

Thank you KootK, I see where the moment comes from and the breakout cone now. I haven't checked PCI yet but will look into it, that you for the suggestion.

TXStructural, thank you as well for the response. I'll discuss the drawbacks of this connection with the engineer I'm working with. We're actually checking a head-knocker issue with the stairs but thought we'd look at this as well since it's part of the load path and it struck us as unusual. I'll check the section in ACI you referenced as well and if we don't find the capacity we need or even if we do, we may talk with the original EOR about this connection.