Embedment depth for concrete breakout strength 3

[DTS419]

In ACI 318-14 17.5.2 Concrete breakout strength of an anchor in shear, the only time the embedment depth of the anchor (h-sub-e) comes up is in Fig. 17.5.2.1a. However, in this figure it is not clear how the embedment depth relates to the depth of the failure zone, shown as 1.5 * ca1 (edge distance).

In Fig. R17.5.2.1b, the critical depth is defined either by the member thickness (h-sub-a), or 1.5 * ca1 and embedment depth is not a factor in either.

Let's say you had a relatively large edge distance, but a very shallow anchor embedment depth. You would calculate the same breakout strength based on the edge distance whether the anchor is embedded 8" or just 1/2" which doesn't seem right, so I must be missing something.

How does embedment depth relate to the depth of the failure zone and breakout strength of the anchor?

 

[WinelandV]

DTS419,

The depth of the shear anchor has no effect on the concrete breakout strength of anchor in shear (17.5.2). But, that's not the only shear failure mode you need to check

The embed depth will come into play when you get to concrete pryout strength of anchor in shear (17.5.3) Eqn 17.5.3.1a needs the capacity N_cp. 17.5.3.1(a) states "For cast-in, expansion, and undercut anchors, N_cp shall be taken as N_cb determined from Eq. (17.4.2.1a)..."

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

 

[Eng16080]

Luceid, I think he means an anchor in shear, not tension.

DTS419, The breakout area for shear, Avc, (shown in figure R17.5.2.1b) is not related to the embedment depth at all. However, in calculating the concrete breakout strength in shear, Vcb, the value Vb (per Section 17.5.2.2) does account for the embedment depth, to some extent, through the le term.

Perhaps more importantly, though, if you're calculating the shear capacity of an anchor in concrete, you also need to check the concrete pryout strength per Section 17.5.3. This is roughly the same calculation as the breakout capacity in tension, and the embedment depth is a major factor in that.

EDIT: Ok, WindlandV beat me to it, ha ha!

 

[Luceid]

Ah - botched it. Gonna remove my posts for clarity

 

[DTS419]

Yeah, I'm aware of the other failure modes, but when I look at Fig. 17.5.2.1a it is hard for me to wrap my head around the depth of the anchor NOT influencing the breakout cone.

 

[canwesteng]

The influence of embedment depth on shear breakout strength is accounted for in 17.7.2.2.1 in the V.b value. It does increase shear breakout capacity up to a point, but does not increase the size of the breakout cone.

 

[DTS419]

So if I had an anchor with 12" edge distance but it was only embedded 1/4" deep, it would still develop the breakout cone down to 18"?

 

[WinelandV]

It would fail in pryout before it created the breakout cone. So, no. It wouldn't develop the breakout cone.

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

 

[DTS419]

The influence of embedment depth on shear breakout strength is accounted for in 17.7.2.2.1 in the V.b value. It does increase shear breakout capacity up to a point, but does not increase the size of the breakout cone.

What version of the code are you referring to? That's not in 318-14.

 

[WinelandV]

canwesteng is referencing 17.5.2.2, Eqn 17.5.2.2a, which contains l_e, which is h_ef for anchors with a constant stiffness over the full length. However, l_e is limited to a max of 8*d_a.

Good catch by canwesteng. Sorry I missed that.

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

 

[canwesteng]

I was using 318-19, but probably have a typo in the reference too. I default to 19 because it has more stringent requirements for strut and tie designs, although I guess it probably isn't in force in lots of places.