What is the prestress force in HST 3-R M8 tightened with 20Nm torque specified in the technical data sheet? The concrete is C25/30, cracked.
Dear Huong Tran, thank you for waiting!
Calculating the prestressing force in an anchor can be a difficult subject. To know the exact prestress force in an anchor, online tests should be performed. Nevertheless it is possible to give a rough estimate of the prestressing force.
A way to calculate a prestressing force in an anchor is with the following formula:
P=Tr/(ku$*D)
-P= prestressing force in an anchor
-Tr= torque applied in the post-installed anchor
-ku= proportionality factor made out of tests, for post installed anchors will it be around 0.3
-D is the nominal diameter of the anchor.
Depending on the anchor the proportionality factor can differ. On average it will be 0.3.
In this case the prestress in your anchor will be 8.3kN.
Hilti BELUX Engineering Team
Dear Huong Tran, first of all thank you very much for asking the question via AskHilti and apologies for a reply that comes in later than usual due to the holidays.
To give a correct answer to your specific question we are currently verifying a factor in the formula that needs to be checked. We will come back to you here with an answer the day after tomorrow latest.
Thank you!
Belux Engineering Team.