Hilti Profis Anchor in Shear

[ChangeOrder]

When checking Hilti anchors in Profis, it is drastically conservative on shear when grout is used. Typically, I use 80% of the strength of the anchors without grout. Is this a common problem?

 

[jayrod12]

Isn't the issue bending in the anchor bolts amplifies the shear force in prying? They assume all it does it move the application of load above the face of concrete.

I would be more inclined to trust their software, since their capacity are based on testing and they wrote the program to align with the results of their testing.

Where did you come up with the 80%?

 

[Celt83]

Hilti has adopted the ETAG Annex C provisions for stand off anchors with grout which can give conservative results under some conditions. AISC Design Guide 1 has provisions for checking the bending of the anchors for standoff conditions which can also significantly reduce the shear capacity.

I'm making a thing:

http://www.thestructuraltoolbox.com

(It's no Kootware and it will probably break but it's alive!)

 

[ChangeOrder]

section D.6.1.3 Appendix D of ACI 318-11 just requires the shear capacity to be multiplied with 0.8 when a grout pad is used.

 

[dold]

It's considering the bending in the bolts. Print out one of the detail reports and there is a little section checking shear+bending interaction of the anchorbolt steel itself. Not sure what effect a standoff has on the concrete failure modes. This always blows up the anchor size. I don't bat an eye when spec'ing 1.1/2" Gr. 105 anchors even for somewhat 'modest' frames, if i'm trying to avoid shear lugs for whatever reason. You'll see much better 'return on investment' with larger anchors vs. larger number of smaller anchors.

 

[Rabbit12]

Ah! This is a pet peeve of mine. Hilti gives no option to use the 0.8 multiplier for shear with built-up grout pads. IMO, sizing anchors for the bending aspect gives much larger anchors than is required by code.

 

[SandwichEngine]

This is why I prefer the simpson strongtie software. It calculates anchor bolt capacity with grout correctly with the 20% reduction in shear strength.

I have this conversation with foundation engineers a few times a year. They always think our anchor bolt sizes are too small because they're using Hilti and haven't ever run the equations by hand.

 

[Eagleee]

ETAG Annex C I think itself follows EN 1992-4. The 'steel failure with lever arm' equations appear in Section 7.2.2.3.2, while conditions for considering or not the standoff / lever arm appear in Section 6.2.2.3. HILTI Profis I think 'navigates' this based on input parameters. AISC i remember being much 'better' as it is noted above.

Seems indeed very conservative, number of anchors needed even for light shear forces sometimes seems a big overkill because of this. Research into this also seems sparse, considering how basic / common it is to use such anchors to transfer shear in light applications.