Pretension for Cast in Place Anchors Under Fully Reversing Load
Pretension for Cast in Place Anchors Under Fully Reversing Load
(OP)
Hi All,
I'm designing an anchor system for an embed that is subjected to fully reversing loads. In a typical bolted connection (steel faying surfaces), this means I would want my bolt pretension to remain larger than my externally applied tensile load (no fatigue loading on the bolt and no slip). We do this by using DTI washers to confirm the bolt is axially preloaded to 70% of it's UTS (typically A325 bolts <= 1in so UTS is 120 ksi). Anchoring a plate into a concrete slab, as I understand, is a different story. I have been using ACI Appendix D to ensure my steel and concrete failure modes have an adequate factor of safety. If I calculate the concrete tear out for a single anchor bolt,I get only about 20 kip (see attached pic for equation and result). Should I be sizing the anchor bolt to ensure that 70% of UTS will never exceed this 20 kip? If the entire anchor group (4 bolts spaced quite close together with lots of cone overlap) can only resist about 22 kip, should the sum of all the bolt pretensions remain below this??
Thanks!
Below is a link to a similar thread.
thread507-252088: Bolt pretensioning / Concrete Splitting
I'm designing an anchor system for an embed that is subjected to fully reversing loads. In a typical bolted connection (steel faying surfaces), this means I would want my bolt pretension to remain larger than my externally applied tensile load (no fatigue loading on the bolt and no slip). We do this by using DTI washers to confirm the bolt is axially preloaded to 70% of it's UTS (typically A325 bolts <= 1in so UTS is 120 ksi). Anchoring a plate into a concrete slab, as I understand, is a different story. I have been using ACI Appendix D to ensure my steel and concrete failure modes have an adequate factor of safety. If I calculate the concrete tear out for a single anchor bolt,I get only about 20 kip (see attached pic for equation and result). Should I be sizing the anchor bolt to ensure that 70% of UTS will never exceed this 20 kip? If the entire anchor group (4 bolts spaced quite close together with lots of cone overlap) can only resist about 22 kip, should the sum of all the bolt pretensions remain below this??
Thanks!
Below is a link to a similar thread.
thread507-252088: Bolt pretensioning / Concrete Splitting






RE: Pretension for Cast in Place Anchors Under Fully Reversing Load
Can you use a long anchor in a sleeve? That way you can design it for whatever pretension you need.
RE: Pretension for Cast in Place Anchors Under Fully Reversing Load
I also need that pretension to make sure my connection doesn't slip and load the bolts in shear. So you're not sure if pretensioning anchors can result in a non slip connection? I'm curious to know if there's a code for this. I have a paper by R. Cook and R Klinger, "Behaviour of Ductile Multiple-Anchor Steel-to-Concrete Connections with Surface-Mounted Baseplates" that states they got on average a coefficient of friction of 0.4. This is better than the Class 'A' coefficient of 0.33 between two steel surfaces.
On another note, these sleeves are required to ensure there is no bonding of the thread to the concrete? I think this ensures the entire bolt is being elongated under the axial pretension? Are these sleeves a standard part to spec? If they're not on Mcmaster Carr I'm skeptical :)