hole size in concrete for epoxy anchor ... tolerance ?

[xtal01]

We are about to fasten down the sill plate (pressure treated wood) of a new building (concrete pad).

We plan to use hot dipped threaded rod.

We looked at installation instructions for a few epoxy anchor cements (two part).

Problem ... they all give a general note ... 1/2" and under ... hole plus 1/16 .... 5/8" or larger ... hole plus 1/8

No real tolerance.

I looked all over the web and could not find any information on how hole size affects pull out strength.

We did find a general note saying most hammer drills are designed to cut oversize (example 1/2" ... .520 to .530 dia)

I am sure this is not super critical or they would be more specific but I wanted to check with you guys ....

Is tighter better (assuming you make it large enough to get epoxy all around).

I think last time I did this (probably 10 years go ... still holding strong), I just drilled a 1/2" hole for a 1/2" bolt (I am sure it cut over size as the rods dropped in).

Should I be drilling a larger hole?

If so, why? I would think the less epoxy the better (again assuming 100% converge / contact) ... or am I wrong?

I do see lots and lots of notes and warning about how clean the holes must be so I realize this is critical.

Probably overthinking this but I want to make sure it is done right.

Thanks .... Mike

 

[Agent666]

Most anchors documentation I've seen have the hole diameter specifically noted. For example a 16mm anchor requires a 18mm hole, for a 20mm anchor requires a 24mm hole, etc. So check the approvals for the anchors you are using.

The hole diameter should be part of the underlying testing to the products ETA or other approved methods. This is to ensure the on-site installation is in accordance with the limitations under which the performance is proved via testing.

Having said that, I'd imagine having the hole slightly over sized with a chemical anchor isn't so bad. For a mechanical anchor it's a lot more critical.

 

[dik]

I suspect, that under load, the thinner the epoxy joint the less likely it is to creep... but, I don't know for sure...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[SwinnyGG]

Every anchor I've ever used, even low quality anchors, have specified a drill bit size on the box. For jobs where all the right steps are actually taken, the required hole is specified as a drill size in the submittal information.

Hilti knows that if you drill a hole with a 5/8" rotary hammer bit, the hole you get is going to be 0.645-0.655. Follow their directions for drill sizes and you'll be fine. Deviate from their directions, and you now own the performance of the anchor, which you don't want.

 

[xtal01]

Thanks ...

I guess that was my real question was ... how critical is the diameter ... and is it better to be under or over (obviously it is best to be spot on the specifications).

As you guys pointed out .. the house size needed is specified.

That said, I build in a world where I am lucky if I can get builders to follow directions. This is a residential building in rural VT ... we don't even have inspectors here and buildings don't require any engineering approvals ... not even to get permits (just draw a square on the plot to show us where it is going).

As you said, my guess is companies like Hilti must know this, do all kinds of testing and give a large safety factor.

I can just picture an 18 year old kid moving a drill all over after telling him to hold it straight and clear it often.

I was tempted to got with something like the Simpson HD Titan fasteners but I am not sure I would have much more luck ... in fact my guess it the hole diameter would be even more critical.

Thanks!

 

[EdStainless]

Epoxy anchors are very tolerant of hole size variation.
Yes, too small (there is a minimum bond thickness) to too large will reduce capacity, but not abruptly.
Much more forgiving than mechanical anchors.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dvd]

What did the application engineer at Hilti, or other, say?

 

[xtal01]

They don't want to give an answer ... don't blame them.

They simply said to follow the recommended hole size.

Well of course I will do that.

One did write anything outside the parameters given would need to be evaluated by and engineer ... not going to happen on a simple workshop / garage build.

Honestly, if you think of the guy who has a few guys and builds houses, you really need to wonder how many houses "completely" meet code.

I know a few times I have asked questions during a build and been told things like "we always do it this way" ... or "don't worry, there is a safety factor" ... or " the last one we built is still standing" ....

Many places like where I live don't even have inspectors ... that is scary ... they "self regulate" ... kind of like Boeing (and how did that work out) ....

 

[dvd]

I'm going to hazard a guess that ACI 355.4 has some information pertinent to your inquiry. Don't have access to it, you could probably call ACI and talk with someone who could advise you on what standard to buy. See discussion under 1.2.1 in this preview.

 

[Agent666]

The ACI requirement is just an upper limit that manufacturers/suppliers should adhere to. The manufacturers/suppliers may of course have more stringent requirements as these things are tested and have recommendations based on those approvals.

Basically, stick to the supplier's requirement, that's the basis of the strength someone designed for/to.

Having said that, the ACI requirement of max size being 1.5 times bolt diameter is a pretty large tolerance.

 

[xtal01]

WOW ... that is a very large tolerance.

I was worried that if it says plus 1/16" I could be only plus 1/32" or be maybe plus 1/8"

Like I said, I will aim for the recommended hole size .... just overthinking the situation ... probably looking for a problem that isn't there.

Thanks for all the advice!

 

[racookpe1978]

No, no you are not "overthinking" the situation, but are being careful before the situation occurs.

It really comes into play though when the "wrong hole" has already been drilled, and you (the "engineer" has to come back with an answer.
If too little, get the right drill bit for the epoxy specs, and drill it out again. CLEAN THE HOLE, (dry if required), and use the epoxy and the right threaded rod/anchor bolt.

If too big, consider the loads involved. It will generally be better (stronger) to use the next larger anchor bolt/threaded rod diameter - the rod size for the hole as-drilled - and the epoxy package needed. (You might need the next larger epoxy package, but probably not. Using a larger threaded rod might required redrilling the steel plate, but that reduction in the plate edge limits should be minor compared to the overall plate thickness and width.
Thus, it is far better to replace a 1 inch threaded rod with a 1-1/4 threaded rod, than it is to use a 1 inch threaded in a 1-3/8 hole. The 1-3/8 hole is the proper hole for a 1-1/4 rod.