Static tension on embedded anchors
Static tension on embedded anchors
(OP)
The backspan of a cantilevered roof beam is going to place tension on some anchor rods I'm placing the in top of a concrete column.
Anyone have some tried and true pretensioning methods/notes for anchor rods they'd like to share? I just want enough to compensate for creep.
Anyone have some tried and true pretensioning methods/notes for anchor rods they'd like to share? I just want enough to compensate for creep.






RE: Static tension on embedded anchors
A code treatment of the question must be dealt in one "anchors to concrete" viewpoint for which the ACI code has a number of equations, and anchors providers have software for. This would be enough for the introduction of forces, but I would also consider what described above and would ensure that enough column shear reinforcement exceeds the anchors' length since there a complicated stress state occurs, from anchoring the tensioned rods and concurrent directly imparted shear.
If what I describe does not correspond to your problem, please provide a sketch for clarification.
RE: Static tension on embedded anchors
My question is really one of what methods are employed to develop pretension in embedded anchor rods. The uplift force is not large (<10k total, serv.) Since in this instance I also am having to detail for future expansion, I'm thinking about placing a lenton coupler on the ends of my main column steel, and then coming back with little projections of weldable rebar which would thread into the lenton splice and be welded off to the beam base plate. That gets me out of worrying about pretension and creep, and gets the force directly into the main column steel.
RE: Static tension on embedded anchors
Here is their web site:
http://www.rlrowan.com/canister-bolt
If the canister doesn’t meet your needs (for whatever reason), you can always use embedded plates. In any scenario (for embedded anchors) you can minimize creep by using a low ratio of the total capacity of the connection (based on the research I’ve seen).
RE: Static tension on embedded anchors
RE: Static tension on embedded anchors
RE: Static tension on embedded anchors
I don't see that this will eliminate creep however.
RE: Static tension on embedded anchors
The pretension would just be enough to keep the bolt permanently clamped--that is, that creep over time would not be enough to completely remove the clamping force of the beam connection. Since I have net tension under dead load it's only when the load reverses under wind upift that the bolt could then lose tension. I just want it to stay clamped, even if only slightly.
I'm guessing there's some sort of spring loaded nut I can use to accomplish this as well. Just have to find it.
RE: Static tension on embedded anchors
RE: Static tension on embedded anchors
Here's my thought process.
1. Don't want the nut to come off, or loose, if connection cycles between applied tension and applied compression. Tension will be normal (gravity load) state.
2. Pretension - how do I do that?
3. If the anchor is in tension, how much do I have to worry about creep? At some level it's negligible. Also at some level of pretension, the creep won't overcome the tensile force in any reasonable time frame.
RE: Static tension on embedded anchors
So given that (if you are worried about the nut loosening) you could set your target pretension force (which I have normally specified as a percentage of the anchor bolt yield stress) to the maximum tension force the anchors will develop in its service life + the % loss I discuss above and I would assume you would be covered.
As an additional safety factor, I have sometimes specified periodic inspection (with critical equipment) of the bolts to be sure it is maintain that pinching force.