Deep embedment of anchor for capacity

[JStructsteel]

I have a 1" anchor that needs to be epoxied into a 10" thick wall for a hold down at a shear wall. I tired PROFIS and no go. Is there any literature for deep embedment with epoxies?

 

[a_urbs]

Could you provide a sketch? Maybe another configuration could solve your problem. What's the required hold-down force?

 

[RWW0002]

A Holdown requiring a 1"Ø anchor may be carrying a pretty real load. I have had some luck getting test data for embedments>20db (max embed per Hilti) in the past, however in this case it may not be enough to get the load you need. I would contact Hilti, Simpson, Powers, etc and see what they have on file that meets your condition.

If you are close to maxing out a 1"Ø anchor, I doubt you are going to get breakout to work in a 10" wall. My thought would be to try to lap the anchor with vertical reinforcement within the wall. ACI has a method for developing vertical rebar each side of the breakout cone (See ACI-318-19 17.4.2.9), but it is intended for headed anchor rods. A similar theory might be able to be applied to epoxied anchors, but I am not aware of much literature on the subject.

If this wall is not in place yet I would think seriously about cast-in place solutions.

 

[JStructsteel]

Here is the detail. 11.4K uplift. This is a SIP panel home. SIP engineer washed their hands of anchor design (probably knowing it wont work).
Wall is poured, slab i am not sure about.

If slab isnt poured, I thought about some horizontal bars tied to the bent bars into the slab to help with breakout.

 

[RWW0002]

Yikes - It sounds like they put you into a pretty tough spot. It is going to take quite a bit of footing/wall/slab to resist 11.4k of force, especially if you are trying to use 0.6D..

Maybe you can add concrete to each side wall here that encompasses the wall pour, adds some ballast to resist the uplift force, and restrains the breakout a bit. It may take a decent chunk of concrete, but might be the easiest solution.

 

[JStructsteel]

The footing issue is secondary, if I cant get the load into it.

I think I will have to get with Hilti and see if they have any recommendations for a deep embedment.

My other thought is to change the shear walls to another CIP pour. At least then I can embed a anchor rod at the top when they pour it. Good luck though getting in the right spot.

As always, residential construction is a shit show. Had to get the footings installed before the panel design was done.

 

[TRAK.Structural]

Any chance you can get the SIP panel design changed? Looking for options to use multiple smaller diameter hold downs?

 

[CDLD]

you might be able to “lap” the anchor with the vertical wall reinforcing to preclude breakout.
Hilti has a technical guide with examples for this situation. They also have a free software for this.

 

[JStructsteel]

Any chance you can get the SIP panel design changed? Looking for options to use multiple smaller diameter hold downs?

Panels are pretty much set in stone for the openings. The shear wall at this area is small, carrying alot of load.

 

[JStructsteel]

you might be able to “lap” the anchor with the vertical wall reinforcing to preclude breakout.
Hilti has a technical guide with examples for this situation. They also have a free software for this.

I will look into this. Probably the way to go.

 

[CDLD]

If you are not very familiar with “anchor reinforcing” (which is basically “lapping), good starting points are AISC Design Guide 1, Companion to ACI 318, PIP STE0 5121, ACI 318-19, and of course the Hilti technical guide. Most of these articles are for “lapping” cast in anchors but I am hopeful you’ll be able to find something for lapping post installed anchors.

 

[RWW0002]

"Lapping" with rebar is similar to what I referenced above (anchor reinforcement). The "codified" method is for headed studs with a breakout cone and should not be aplied directly to epoxied anchors without some thought. The mechanism is a bit different. I would not be surprised if Hilti had a technical guide that applies a similar approach to epoxied bars. I think there is some logic to treating epoxied bars similar to developing rebar, but I have not seen a ton of guidance on this. Ideally the anchor is fairly close to existing dowels, otherwise this might be difficult to make work (think non-contact splices).

If you have a hard time getting it to work out, you might look at the "concrete chunk" I sketched above as a backup plan. If you could get the wall and concrete chunks to act together you might be able to effectively control concrete breakout and use traditional eopxy embedment calculations. Just a thought.

 

[TRAK.Structural]

Agree with RWW, I've gone down the "lapping" concept and tried to apply it to post-installed adhesive anchors but the hiccup for me has always been finding a clear path to this approach being codified. If you are going to need the additional mass for uplift restraint anyway than I think the extra concrete to prevent breakout makes a lot of sense.

 

[Eng16080]

I think I will have to get with Hilti and see if they have any recommendations for a deep embedment.

Good luck. Unless you can drill down and epoxy to the footing, I doubt you'll be anywhere close to the capacity you need.

The best I can come up with for a potential solution (other than demolishing and pouring new concrete with cast-in anchors) is:

1. Weld to existing rebar in the wall. Although it appears there isn't much.
2. Add a steel strap down the face of the wall and epoxy anchors from the side.

I recently had a job where I needed to hold-down a narrow shear wall panel (Simpson strong wall). Even with cast-in anchors, this is what was required:


(As a side note, the contractor apparently didn't use my plan and set the anchor bolts with about 10" embedment and in the wrong locations per plan view, so the wall panels won't even fit. And for some icing on the cake, the building inspector gave it all the ok while looking at this plan. Some days I just don't know. End rant.)

 

[dik]

I don't know if this is the same.

https://www.sciencedirect.com/science/article/abs/pii/S0950061822007784

I haven't used them for years, but a corrugated plastic duct could be purchased and the rebar was grouted into it to develop tension loads connecting precast to CIP stuff. It was occasionally used for fairly high tension loads. I haven't done any serious concrete design for decades, so I'm not sure what it was called or if it is still available.

 

[JStructsteel]

I like the idea of straps each side of the panels to the footing. Im sure I can get that to work. Just have the issue of protecting it from the elements.

Or, if the slab is not poured, put a anchor each side to take the load, the door/window jambs can cover the straps on the studs.

My HDU14 on the non door side, and then a HTT5 on the door side/window side and pour the slab over it. Would require some proper layout for the contractor to get everything in right spot (anchor drilled in, sticking out of pour)

Should be pretty darn close with the combination of anchors.

Thanks. Contractor called yesterday at 4PM, but was in party mode so didnt take his call. Will find out Thursday.

 

[EngDM]

"Lapping" with rebar is similar to what I referenced above (anchor reinforcement). The "codified" method is for headed studs with a breakout cone and should not be aplied directly to epoxied anchors without some thought. The mechanism is a bit different. I would not be surprised if Hilti had a technical guide that applies a similar approach to epoxied bars. I think there is some logic to treating epoxied bars similar to developing rebar, but I have not seen a ton of guidance on this. Ideally the anchor is fairly close to existing dowels, otherwise this might be difficult to make work (think non-contact splices).

If you have a hard time getting it to work out, you might look at the "concrete chunk" I sketched above as a backup plan. If you could get the wall and concrete chunks to act together you might be able to effectively control concrete breakout and use traditional eopxy embedment calculations. Just a thought.

Have you come across a reference that goes over the breakout cone for epoxied anchors? I was under the impression that if your adhesive worked, then your forces transfer to the surrounding concrete. Is the issue that the tension is resisted along the anchors length, whereas headed anchors are held down at the end of the anchor by concrete in compression?

I guess in the adhesive's case it's more of a breakout bubble and not a cone that goes up at a 35° angle or whatever your relevant code deems.

 

[driftLimiter]

Adhesive anchors bond along the depth of the anchor and there is a limit state for that. There is also a limit state for concrete breakout.
ACI treatment of concrete breakout is the same for headed anchors as adhesive anchors.

Ref: ACI 318-19 Section R17.6.5.1 this commentary section may be useful in thinking about the differences.

For headed anchors we have an anchor pullout limit state that is somewhat similar to bond failure for adhesives.
Ch17 doesn't use the Bearing area of the head in concrete breakout failures, but it does show up in the pullout and sideface limits.

@jstruct have you run an epoxy check as if embeded into the footing itself? If that works then I would be partial to a deep embedment. If you want to lump concrete around the sides for mass that could work. Or the footing can act like a beam to resist the uplift.