Post-installed or cast-in anchor? 2

[DTS419]

Let's say a 3/4" hole is formed in precast concrete slab so that a 1/2" or 5/8" bolt can later be inserted through the hole to be an anchor. Would this anchor be considered cast-in or post-installed for the purpose of determining factors per ACI 318-19 Ch. 17?

An argument for considering the anchor to be cast is that since the hole is pre-formed, there is no stress induced in the concrete by drilling of the hole, which seems to be a consideration in R17.6.2.6.1.

An argument for considering the anchor to be post-installed is that the anchor does not benefit from cement bond, although for a short anchor with minimal development length, this seems unlikely to be significant.

 

[jjl317]

Personally, my initial thought is that ACI 318 doesn't really address this case, so I would say neither.

And I have a hard time envisioning a scenario where I think this would be a good idea anyway. Why not just use a cast-in insert instead of a cast hole?

 

[KootK]

How is the hole "formed". Will it be by way of a sleeve that will be permanent?

We're talking about a wedge style anchor?

Is the anchor going into the thin concrete over / under plank cores?

 

[DTS419]

Personally, my initial thought is that ACI 318 doesn't really address this case, so I would say neither.

And I have a hard time envisioning a scenario where I think this would be a good idea anyway. Why not just use a cast-in insert instead of a cast hole?

Then how would you determine capacity if not ACI 318?

 

[DTS419]

How is the hole "formed". Will it be by way of a sleeve that will be permanent?

We're talking about a wedge style anchor?

Is the anchor going into the thin concrete over / under plank cores?

Just a solid concrete slab, say 3-4" thick. Hole is formed by a plastic tube that is removed.

 

[KootK]

So is this a wedge anchor or an adhesive anchor? You said that the anchor wouldn't benefit from bond stress which suggests a wedge anchor. And, if that's the case, I'd lean towards post installed. That said, there is certainly some merit to @jjl317' s argument that this situation is not a perfect analog for either condition.

 

[jjl317]

I likely wouldn't, as I would either use a cast-in anchor, or use a post-installed anchor (with a removable component if need be).

Some context might be helpful - and if you are trying to justify via ACI, the answers would likely depend on the load direction (i.e. Tension, Shear or Both)?

 

[DTS419]

So is this a wedge anchor or an adhesive anchor? You said that the anchor wouldn't benefit from bond stress which suggests a wedge anchor. And, if that's the case, I'd lean towards post installed. That said, there is certainly some merit to @jjl317' s argument that this situation is not a perfect analog for either condition.

It's simply a bolt inserted through hole in the concrete so that it in effect looks like an external headed stud.

 

[ANE91]

Just a solid concrete slab, say 3-4" thick. Hole is formed by a plastic tube that is removed.

Setting aside the very valid question of governance, the smooth-sided hole that you have created is a problem.

Manufacturers used to specify that any anchor going into a diamond-cored (i.e., smooth-sided hole) requires the hole surface to be roughened. There exist drill inserts which look like cylindrical tuning forks with nubs on the ends, and these can “beat up” or lightly scarify the hole surface when inserted into a hammer drill. This was required for adhesive anchorages, at least. I haven’t kept up with the technology.

These days, it could be the case that the manufacturer will permit use of the smooth-sided hole while taking reductions in anchor capacity.

However you decide to proceed, be it cast-in or post-installed, you must acknowledge the mechanics of the situation, in that your hole is smooth-sided and lacks the keying action that is provided by rough concrete. We learned the importance of hole preparation the hard way. See Big Dig. (Yes, I know that hole cleaning and epoxy run-out were the main issues, there.)

 

[DTS419]

Guys, this is getting rather over-complicated. It is simply a headed stud that is in a pre-formed hole rather than cast in to the concrete. There is no adhesive or need to roughen anything. This is done by a pre-caster and has been done tens of thousands of times. Just looking to establish whether this headed stud anchor should be treated as cast vs. post-installed, mainly for 17.6.2.5 and 17.6.2.6, to determine how much tension I can apply to one.

 

[phamENG]

Can you provide a sketch? I'm envisioning some sort of through-bolt in this precast slab, which would be totally different from what everyone else has been talking about.

 

[driftLimiter]

You've tried a verbal description and your not getting the answer you want. Perhaps if you show us a sketch of the bolt and its loading conditions you can get better answers.

DTS416: It's simply a bolt inserted through hole in the concrete so that it in effect looks like an external headed stud.

So you are saying stick a bolt in a clean hole and it is supposed to carry tension?

I don't understand how the load is transferred to the bolt. Is it a through bolt with a washer, is it a pin in shear?? Is it a formed bearing inside the concrete for the bolt to 'pull on?' WTF is it???

Generally precasters use anchors that are qualified by testing, and parameters are provided to reconcile the ACI Ch 17 calculations.

 

[jjl317]

is this what you mean?

 

[ANE91]

ACI 355.2 qualifies the use of post-installed mechanical anchors, and ACI 355.4 does the same for adhesive anchors. If your application does not meet the assessment criteria of either of these standards, then it is not considered a post-installed anchor subject to the provisions of ACI 318. Refer to 17.1.2 for what ACI 318 covers, and refer to 17.1.5 for what ACI 318 does not cover.

I think this ultimately boils down to your engineering judgment.

Guys, this is getting rather over-complicated. It is simply a headed stud that is in a pre-formed hole rather than cast in to the concrete. There is no adhesive or need to roughen anything. This is done by a pre-caster and has been done tens of thousands of times. Just looking to establish whether this headed stud anchor should be treated as cast vs. post-installed, mainly for 17.6.2.5 and 17.6.2.6, to determine how much tension I can apply to one.

 

[EZBuilding]

Based on the description provided; I would consider the connection to have zero tensile capacity.

 

[Eng16080]

I don't understand how the load is transferred to the bolt. Is it a through bolt with a washer, is it a pin in shear?? Is it a formed bearing inside the concrete for the bolt to 'pull on?' WTF is it???

Ok, so I'm not the only one losing my mind trying to understand this connection!

 

[Eng16080]

If it's this: then I don't think ACI Chapter 17 would technically apply, although I imagine you might get a reasonable result still using Ch. 17 with an embedment depth equal to the slab thickness in this case. Otherwise, I suppose just check concrete bearing at the washer, punching shear, and bending of the washer.

 

[SWComposites]

This is not an "anchor"; it is a bolt in a hole. The precaster or someone will need to generate some test data for the specific panel thickness, hole size, fastener diameter, washer diameter.

 

[DTS419]

is this what you mean?

View attachment 3754

Yes, this!

 

[DTS419]

If it's this: View attachment 3755 then I don't think ACI Chapter 17 would technically apply, although I imagine you might get a reasonable result still using Ch. 17 with an embedment depth equal to the slab thickness in this case. Otherwise, I suppose just check concrete bearing at the washer, punching shear, and bending of the washer.

Yes, this is exactly the scenario. The sketch shown here is almost identical to the ACI figure showing a headed anchor bolt (Fig. R17.6.2.1). The only difference is that a cast-in headed bolt is embedded in the concrete whereas this one passes through it. The load is transferred from the bolt to the concrete by bearing on the head of the bolt, which will induce a breakout cone like a headed anchor.

If we can at least establish that this is a form of an "headed bolt" as ACI 318 Ch. 17 uses the term, then the question is whether we use factors for cast vs post-installed....