Hi,
We are interested in the prestressing force values for anchor bolts, specifically the M16 bolts / 8.8 and 5.8 grades.
Kind regards,
Ash
Hi Ashkan,
Thank you for contacting Hilti.
I'm not sure if I understood your question correctly, therefore I've sent your contact to one of our field engineers who will contact you directly.
From our understanding, pre-stressing the anchors is linked to the relaxation of the installation torque due to the initial creep of the chemical. Chemical anchors can mostly exhibit symptoms of creep if loaded or tightened before the appropriate curing time is reached.
Moreover, creep and relaxation are considerable, so that the pretension created by the tightening torque can be reduced to 30% to 50%. Our anchor technical data take this into account: Prequalification tests (e.g. for ETA’s) are made by torqueing the anchor to the recommended installation torque, then loosening the nut and retightening it to only 50% of the recommended torque. Only then load testing is performed.
I hope the above is helpful.
Kind regards,
Ask Hilti team