Hilti Profis

[Lion06]

I talked to Hilti last week regarding an (extremely conservative, in my opinion) assumption that it makes when looking at shear breakout.

The issue is that Profis assumes, for shear breakout checks only, that the leading anchor takes the entire shear load. I believed that this was a mistake, so I called them first. The woman I spoke with asked me to send the file, which I did. I also explained the issue in the email.

I got a reply today stating that they prefer to do it this way to be conservative. They don't believe ACI is wrong, they just prefer to be conservative. So, apparently it wasn't a mistake, they just want to be even more conservative than App. D apparently already is.

I only bring this up so that if you use Profis you can keep this in the back of your head when designing anchor embedments.

 

[RLC32681]

StructuralEIT,

Thanks for the information beacause last week HILTI presented there products in our company. We are planning to use HILTI profis in designing anchors bolts. I am just curious with your developed spreadsheet because I am presently developing a speadsheet for anchor design. Can you please share your speadsheet if you dont mind? I just want to see the results and check by myself.

 

[Lion06]

How far along are you in your spreadsheet?

 

[csd72]

There is actually a reason for this assumption regarding chemical anchors.

When you design a steel to steel connection the holes will be in good alignment with each other and as the bolt relies on bearing on the edge of the holes then the shear in the bolts will be roughly equal.

Now, for an end plate with chemical anchors the location of the anchors is not in the same place in each hole and you will therefore receive more uneven loading between them. Yes taking all the shear on two anchors is probably conservative but taking the loads evenly is probably unconservative.

 

[Lion06]

They do it for ALL anchors, not just post-installed anchors. Additionally, don't you have more control of the hole placement for post-installed anchors? I'm picturing the typical baseplate with 4 anchors sticking up out of the pier/footing. I don't believe that they bear on the edge of the holes any better than post-installed anchors will.

 

[RLC32681]

Actually I just started conceptualizing how will I undergo the programming. I am only considering mechanical anchors.

 

[miecz]

StructuralEIT

Could you post a sketch and the Hilti solution? I've developed Mathcad Solutions to Appendix D and would like to use this example for debugging purposes.

 

[Lion06]

Here is Hilti's output. I made a note where the issue is.

 

[racookpe1978]

OK, so Hilti is "conservative" when trying to predict (not calculate) shear in their anchor bolts.

That's not really a bad thing - considering that their equations are going to holding up things above people's heads and property.

But think about this particular shear prediction: Shear is rarely the limiting issue in concrete anchors; Prying is the limiting value (pulling the anchor out of the surface of the concrete, rather than cutting the anchor bolt in half due to shear loads.) So, since shear isn't a limit, why not check the connection array for shear conservatively?

---

Now for prying, the real problem is trying to (accurately enough!) predict the LOCATION of bending line of the anchor plate under the actual ultimate moment load; the direction of the ultimate bending moment load; the actual amount of the bending moment; the resistance of the anchor plate to bending about that (unknown and only guessed at) bending (line) location; and the strenght of the concrete, concrete-to-bolt, and bolt+nut strength that are resisting the (unknown but guessed at) bending moment at the (unknown but guessed at) bending line location.

With those unknowns, why not accept a conservative but widely accepted value for shear resistance frm the actual vender you are using?

 

[sandman21]

He is not talking about pryout, which rarely governs shear limit states, the one which normally governs is shear breakout, which is even more conservative than tension breakout, if anyone can believe that. Just to give you example had to check a beam connection and embed plate with 6 HSA 9" spacing, for about 13k at the top of a 14' wall loaded towards the foundation, both Simpson and Hilti said the connection fails under D+L. I would love to see a shear breakout test on a 14'x8" THK. wall. This is way beyond being conservative just because the behavior is not clearly understood.

This is not the fault of either Hilti or Simpson or them just wanting to be conservative, they have not been given direction from ACI on how they should handle shear load distribuation. The most they have touched the subject is in the commentary in fig RD.6.2.1(b) of ACI 318-08 unless the anchors are rigidly attached case one is used. They are currnetly working with ACI to determine how the loads should be distributed to the anchors until they are given guidance they have chosen this route according to there rep.

StructuralEIT, talk to the local field rep. they are the ones with the correct information, I never call Hilti. I always get a salesperson and it takes forever for them to get back to me. I can give you contact to our rep on the West coast he can give you better help you or give you contact information for the rep in your area.

 

[Lion06]

Sandman-

I actually talked to, and got a reply from, an engineer from Hilti. My spreadsheet gives you the option to neglect shear breakout if there is no free edge (as the example you have given). If you have a wall that goes straight down to a footing, it's impossible to have a shear breakout failure. The wall would have to span to somewhere as a beam and the footing below the wall in which your embed plate is located would have to fail in bearing and displace in order to allow the wall to experience the shear breakout failure.



racookpe-

The issue I was talking about was shear breakout, not pryout. Pryout rarely controls over breakout. Additionally, the prying that you are talking about is a tension limit state, not a shear limit state.
The reason for questioning the output is because that's what engineers do. I don't believe that it's a widely accepted value. This isn't a "Hilti" value anymore, it's a calculated value based on ACI 318 App. D and AC308. Also, when you have the same capacity with one anchor as you do with 20 (literally, I'm not exaggeratint) with the software, I think it's time to question it. When I said conservative, I was talking by a factor of roughly 10, not like 1.2 or 1.5.......... 10. That's a little over the top, in my opinion. It also puts you in a position where you can't get a lot of post-installed connections to work. What do you do?

 

[sandman21]

The only issue is that per the ACI every case must be checked and there is no exception for when it is loaded how I stated. I have had plan checkers require me to check this case. I was alittle mad at the fact I had to do the calc.

 

[Lion06]

I know ACI doesn't explicitly give you the out for your condition, but I don't think it unreasonable to neglect if it can't possibly fail in that manner. Additionally, PCA Notes (I know it is not the code, but it does give good insight) explicitly neglects shear breakout when the shear is not toward a free edge.

 

[sandman21]

Believe me I know it will never fail in that manner and I agree with you; however, the plan checker would not give the detail approval. This was not your typical city plan checker either, an SE. Without an exception, both companies are not going to put themselves out there on a gray area such as this.