Hilti Profis Anchor Design Coefficients

[andriver]

Good-Morning, this is my first post so thank you for the help in advance.

I am using Hilti Profis to help in my first design of post-installed undercut anchors (I mainly deal with steel design).

I noticed that the software assumes a completely rigid baseplate, which distributes tensile loads to my anchors in an unrealistic manner. I have created a finite model to determine the actual distribution of loads to my anchors. I am then doing hand calculations, using the coefficients provided by the Hilti software to determine my concrete breakout strength. I have two concerns...

My "Hilti Design reports" are giving me higher values for several coefficients that I see in ACI 318-08. First, I am seeing a value of "0" for the critical distance where ACI uses 2.5*hef. A value of 0 concerns me, but ACI says if proved by tests other values of critical edge distance can be used (cac).

Next, they have a value of 30 for their coefficient of breakout strength (kc), when ACI 318-08 states "Kc is permitted to be increased above 17 for product specific tests but shall in NO CASE exceed 24". I know Hilti is a trusted name is the anchor world, so does anyone have any incite on these values?

 

[jayrod12]

I don't think the rigid baseplate assumption is all that unreasonable of an assumption. I guess that depends on the amount of moment you're transferring into the anchors but from my experience the baseplate thickness determined via standard methods can be approximated as rigid when determining the anchor loads.

As for the other factors, Hilti does extensive testing and posts all the ICC reports. They are also generally helpful if you give their guys a call with your questions.

 

[andriver]

Jayrod,

Thanks for the input, I think I will give them a call as soon as I have a preliminary design completed.

This is embarrassing, the Kc value of 30 was due to me using uncracked concrete instead of cracked concrete on the drop-down. That issue has been resolved, I now get a Kc value of 24.