Embedded Anchor Design Infinite Edge Distance

[zackngineer]

I was reading this thread: Link

Multiple engineers were using infinite edge distance when running their analysis. At what point/dimension does this become acceptable?

When I tried to recreate their calculations using my software, I was only able to get their designs to work if we treat the edge distance in the shear direction as infinite. If I put any dimensioned edge distance, the designs fail.

 

[lexpatrie]

I think some of these calculations don't apply if there's enough edge distance, but "effectively infinite" I thought was somewhere around 6x the effective embedment. As a general rule it never happens to anything I design, so the intricacies of when the checks don't apply isn't something I routinely encounter.

 

[canwesteng]

Well there's certainly a point where the edge distance won't govern, so you should be able to use a dimensioned edge distance that won't fail. I'm not aware of an actual limit for shear breakout, other than engineering judgement.

 

[Eng16080]

I don't really have a direct answer to your question, but as the edge distance in the shear direction increases, you will likely get to a point fairly quickly where a failure mechanism other than concrete breakout in the direction of the shear force controls. These other mechanisms could be concrete breakout in the direction perpendicular to the shear force, concrete pryout, or a shear failure of the steel anchor.

If your software is only looking at breakout in the direction of the shear force, then I suppose with infinite edge distance, the capacity would be infinite as well. Although, as mentioned, this would be overlooking other failure mechanisms which will control.

 

[Tomfh]

Multiple engineers were using infinite edge distance when running their analysis. At what point/dimension does this become acceptable?

When it may as well be infinite.

 

[driftLimiter]

I encourage you to run through a simple anchorage calculation by hand or spreadsheet. Move the edge distance close to anchor then away from anchor and see how it effects your limit states.

This idea that any number less than infinity causes a failure sounds like some BS to me, something wrong with the software/model/or inputs.

 

[CDLD]

It depends if the sides have close edge distances as well.
Also, if its for an embedded plate on column, than breakout is likely precluded.

 

[icebloom]

There is guidance in some codes and technical publications (eg FIB 58 chapter 10) that for anchor groups with 4 or less anchors and edge distance c>= max(60d_nom,10h_ef) that it may be assumed no concrete edge failure will occur. My understanding is this limited to 4 anchor groups due to the limits of empirical data. Due to the way the equations for shear and tension breakout are formulated, even if you input a very large edge distance it will still flag that you fail via breakout. These are the situations where engineering judgement is required, especially if an element is highly reinforced, on the likelihood of the breakout. Both ACI and Eurocode also have methods (albeit they are very limited in nature) on the design of supplementary reinforcement to resist breakout, which may be helpful.

 

[Greenalleycat]

Depends what code you use as your reference for anchor design
If you have a bunch of anchors in a line then it will often load the front one and say that it fails - it's a pain in the ass

I think the edge distance for 'infinity' is related to the embedment depth, edge distance, and thickness of the slab
I don't have a rule of thumb - I find my stuff is either near enough to an edge that I put in the distance, or it's in the middle of a huge chunk of concrete so it's obviously not influenced by edge effects
It depends on the reinforcement too - if I have a well-reinforced slab with reinforcement developed past the anchor then I may set edge distance to infinity so that it doesn't influence the results
I know that doesn't really answer your question