HILTI Profis Anchor software - design resistance of anchors

[edinmer]

Hello!

I did just a trial calculation in Hilti Profis Anchor software.
I used only one anchor HST-M10 and loaded it with both max. resistance tensile NRd = 6 kN and shear VRd = 18.8 kN load (values are for cracked concrete).
See screenshot.

Utilization is:
Tension: 100%
Shear: 100%

-> both make sense, but...
Tension/Shear Combination is 167%

Does it mean that HST-M10 cannot withstand max. shear and tensile loads if they are applied at the same time?

Thanks for the help!
Edd

 

[KootK]

I think that's exactly what it means.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[edinmer]

Ok.
It's explained on page 43 of "Hilti fastening technology manual".

 

[jrbaus]

If you get really keen, contact Hilti and they will send you information on the ETAG design approach which the software is based on.

 

[mike20793]

The tension-shear interaction is given in ACI 318-08. For T<=0.2Tallowable, the full allowable shear may be used. For V<=Vallowable, the full allowable tension may be used. For all other cases, it is V/Vallowable + T/Tallowable <=1.2. 2/1.2 = 1.67. Thats where youre getting 167% utilization. Hope that helps.

 

[mike20793]

Correction to my above post. It should say when V<=0.2Vallowable. Sorry!

 

[jayrod12]

Mike,

I believe in the updated hilti technical guide it is now (V/Vr)^5/3+(T/Tr)^5/3 < 1. At least for a couple of the adhesives that I spot checked.

 

[racookpe1978]

Plus, those are static "right angle" forces. (There is no "twist" on the anchor bolt and epoxy at the same time as two forces.)

Think about the old mechanics 'addition of forces" that showed the maximum final force is at the 45 deg angle to the member. It would be interesting to see what an actual test looks like, rather than a screen shot of the program page.

 

[mike20793]

Jayrod,

Very good point. ACI 318-11 Appendix D says to use the linear interaction, but the commentary says the parabolic interaction can be used (Hilti uses parabolic for adhesive anchors; I'm not sure about cast in place or post installed wedge/screw anchors off the top of my head. I only included the linear part in my post to show the OP where the 167% utilization came from.

 

[hawkaz]

Edinmer- your title suggests you are mechanical. How well do you understand structural? Please make sure you understand the difference between allowable loads and strength level loads. If you are in a seismic area, make sure you understand the seismic factors. Don't forget to check cracked vs. uncracked concrete criteria also. These items will have a significant impact on your results.

 

[jayrod12]

I was having this debate in the office the other day.

When would you consider the uncracked condition?

I've only determined 2 situations where I would be willing to consider uncracked. The first is an anchor installed into freshly cured concrete in which the anchor will only be used during construction but will not be loaded permanently for the life of the structure. The second is when installed into a compression only member where cracking is unlikely to ever occur due to the confinement provided by the axial load.

 

[mike20793]

I've hesitantly assumed uncracked once in a PT slab. I didn't like it, but we could justify that, at that location, the slab would remain uncracked. I'm hesitant to say anything else is uncracked.