Anchor reinforcement for shear

[BAGW]

Hi,

I am using anchor reinforcement for shear resistance around anchors per chapter 17 of ACI. I am developing the reinforcement on either side of the breakout cone per ACI.

Is there any minimum anchor depth requirement I need to maintain (I typically provide 12" to 18" when no tension and only shear) ? I think its not mentioned in ACI as the break out cone starts at the top of the concrete (where we have top bars to resist the shear) and hence embed length does not really matter.

Any thoughts on this.

 

[WinelandV]

If you look at the concrete pryout strength of anchors in shear, the capacity is based on the concrete breakout strength of an anchor in tension (N[sub]cb[/sub]). You still need to preclude the pryout failure, even with the r/f on both sides of the shear failure cone.

Please note that is a "v" (as in Violin) not a "y".

 

[BAGW]

Agreed. But there is no minimum anchor embedment length I need to satisfy for the anchor shear reinforcement correct.

 

[ENGIRL]

You should be able to determine minimum anchor length by verifying failure modes b and c if applicable.

 

[BAGW]

there is no failure mode "c" as shear reinforcement is provided. And embedment depth does not matter for failure mode "c".

 

[WinelandV]

BAGW,

There's no minimum embed for the shear r/f method that I can see.

Speculating, I think ACI didn't give a minimum since the pryout check will force a de facto minimum. Note also that a lot of the anchor testing was done on small embeds lengths to begin with.

Please note that is a "v" (as in Violin) not a "y".

 

[BAGW]

@WinelandV

Thats what I thought. Thnaks

 

[CDLD]

Bag, you can check the bearing strength of the strut which will bear on the vertical pier rebar and the anchors.
The load bearing length on the anchor is defined in ACI (I think usually max of 8*d and embedment length).
If your anchor length is inadequate for bearing, you may need to increase embedment or anchor diameter.
This photo is taken from PIP STE05121, which gives examples on properly designed anchor reinforcement.

 

[ads0221]

Per PIP we typically do 12 x Da and call it a day if there’s minimum tension.

 

[BAGW]

ACI says the test for R17.5.2.1b(ii) is based on maximum #6 bar. Does this limit us to use bars greater than #6?

Can I use #8 bar and follow all the required shear reinf detail per ACI for shear resistance?

 

[CDLD]

ACI does not recommend it. I would try to make it work with several layers of smaller bars.
You may run into trouble trying to develop #8 bars.

Correction to my last reply - the load bearing length is the minimum of 8*d and embedment length.

 

[BAGW]

How are the shear forces transferred from anchor rod to concrete assuming shear reinforcement is provided?

Is it through bearing of anchor on concrete? Where can I find equation for anchor rod bearing on concrete?

 

[CDLD]

Depends on your setup.
You can have the anchors bear directly on the hairpin or you can use a strut an tie model.
I highly suggest reading PIP STE05121.

 

[BAGW]

If I have a setup similar to ACI R17.5.2.1b(ii) then what happens? Is there a bearing equation for this set up as well? Cannot find anything in ACI for bearing.

 

[HTURKAK]

When you write (Anchor Bolt Design and Installation ) and search the web, one of the outcomes ;

https://tuxdoc.com/download/sabp-q-001-anchor-bolt_pdf

I have downloaded and attached the same. There are some worked examples for this subject.

Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[CDLD]

Bag, looking at ACI R17.5.2.1b(ii), you can probably ignore bearing if you are able to develop the bar on both sides of the breakout cone. Also, the recommendation for using anchor reinforcement #6 or less is only applicable to R17.5.2.1b(i) (ie. the hairpin setup). There is no issue using #8 if you can develop the bars.

The strut and tie model is only needed if you cannot develop the reinforcing on both sides of the breakout cone.
The PIP document goes over both methods (ie. the strut and tie method or the simplified method, where you develop anchor reinforcing both sides of breakout cone).

Simplified method:

 

[BAGW]

@CDLD

This is where I am getting stuck. If I ignore the bearing check, how is the shear transferred from anchor to concrete?

Also do you have the PIP document you can post?

 

[CDLD]

Good question, PIP and ACI do not go into detail about this.
Not exactly sure why there isn't a bearing type check in ACI for shear breakout.

I suppose you could still check bearing over the load bearing length of the anchor (using method I posted above)
This would be sort of similar to how the nut of anchors in tension bear on concrete, which fans out into a breakout cone (ie. pullout failure).
So, if your anchors don't crush concrete locally over its load bearing length (ie. bearing check) and if you anchor reinforcing secures the breakout cone to the rest of the pier you are good (ie. develop both sides of assumed crack).

I would also probably add a couple more anchor reinforcing bars in, especially if you don't take into account the eccentricity between the baseplate and shear reinforcing.

 

[BAGW]

So the bearing are for anchor is pretty much 8 x dia x dia. I wish this was explicitly mentioned in ACI

 

[CDLD]

The load bearing length is calculated as follows:

You may find this link useful if you don't have access to the PIP document:

https://www.sefindia.org/forum/file...nforcement_a_petrolium_project_papers_199.pdf