Anchor Shear Capacity With Grout

[LoneStarEngineer]

In Hilti Profis, the process of calculating shear capacity for anchors sitting on grout follows ETAG 001 Annex C (European guideline- Considers flexure in Anchor). While 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. The difference in shear capacity with a decent shear load (21k) on a sample anchor assembly results in a factor of 5 between the two procedures (With ACI being less conservative).

What are your thoughts on this?

 

[engr.soto]

Does ETAG consider the presence of the grout or just the fact that there is an offset? ACI accounts for the fact that grout adds to the shear resistance. Grout and steel have coefficient of friction of 0.40. I believe the 0.80 accounts for the fact that there is some reduction in the shear capacity due to the presence of bending in the bolt, but it is not a severe as the bending demands calculated using ETAG that don't account for the presence of grout.

 

[ARS97]

I've come across this as well. It's a drastic difference in design outcome. I've contacted Hilti about this in the past and they simply stated that ACI doesn't provide enough guidance on this issue and as a result, use the conservative approach from European technical guidelines.

 

[Klitor]

Did you click on the option that grout keeps the anchor plate horizontal while it slides? It reduces anchor bending moment cca in half (as per etag).