Post Installed Anchors Due to Anchor Misplacement

[HDStructural]

Hello all,

I am working on a small project where we are replacing a few anchors due to anchor misplacement. We will be using an adhesive anchor system. The problem that I am having is that the anchors are only off by 3/4" or so, and are in the way of where the new anchors would be.

Is it possible to do a large core drill of the concrete area (maybe 2" or 3" diameter) that would contain the existing anchor rod. Then epoxy in a new anchor? The issue I see is that the whole would be way too large.

Could I have them roughen the surface around the hole then fill it with concrete/grout and just place the anchor bolt in? Due to the left/right eccentricity of the anchors, we cannot just slot the base plate holes.

What have been your best solutions for these situations?

 

[jayrod12]

Why not just refabricate the baseplate to accommodate the as-installed locations? That's likely what I'd be doing.

 

[HDStructural]

I agree, that would be an easy solution. Our client wants the solution to not touch the steel though, only the concrete.

 

[ANE91]

Look to the epoxy manufacturer. For example, Hilti has addressed this condition in white papers and such. Oversized holes are usually permitted (to a degree) with a commensurate reduction in capacity, though 3” is more than I’ve ever seen. You’re right to think that a cored hole would typically need roughening.

https://www.hilti.com/medias/sys_master/documents/hc2/h5b/9677369933854/Technical-information-ASSET-DOC-LOC-7502228.pdf

I’ve also had success proof-loading anchors that were installed beyond the scope of the ESR.

 

[Tomfh]

Core out the old. Fill hole with epoxy grout (eg fluid epoxy plus sharp sand in a pourable consistency, or a proprietary pourable epoxy grout).. Drill new hole

Or core big enough to cover both both locations, and cast in the new anchor into the epoxy grout.

 

[HDStructural]

Tomfh, that's what I was thinking. How would I calculate the breakout capacity of the concrete and epoxy grout? Or ensuring adequate bond strength of the concrete to grout?

 

[Tomfh]

Tomfh, that's what I was thinking. How would I calculate the breakout capacity of the concrete and epoxy grout? Or ensuring adequate bond strength of the concrete to grout?

Product literature or tech support will usually confirm a producs strength. They are typically stronger than surrounding concrete.

If you roughen up the hole and use a suitable product the epoxy grout plug won’t be coming out.

 

[driftLimiter]

3" diameter core is too big for any epoxied bolt or rebar but, You can use threaded inserts in core drilled holes. HILTI HIS for example. If the geometry works out the old hole could fall within the new core drilled region and you get a clean ESR installation.

When outside of ESR limits I have also had success with proof testing but really its not a fun road to go down.

 

[dvd]

Grouting seems like the way to go - some literature from file attached

 

[Greenalleycat]

This feels like one where you should pushback on the client and get the holes cut into the baseplate
Weld additional stiffeners etc if needed

Epoxy anchor is not a direct substitute for cast-in: it is worse, it is a compromise, and I think it's a lot more effort than core drilling a hole and site welding a 10mm plate washer

 

[Tomfh]

Both ways work. If the client doesn’t want to see a patch job on the baseplate then coring and reinstating the concrete with epoxy mortar is valid.

 

[Greenalleycat]

Just get a strong man and a long bar and kink them over so they fit into the original holes
Best of both worlds

 

[dik]

Can you not drill the base plate to accept the two anchors and weld the anchor rods to the base plate; I always spec that anchor rods have to be weldable... if using ASTM A307, you have to spec it as weldable, or if using ASTM F1554 Grade 55 S1... or HILTI HAS E55 (has to be weldable or grade 55 S1). or is it too late for that.

 

[dik]

3" diameter core is too big for any epoxied bolt or rebar

SikaGrout 212?

 

[HDStructural]

Thank you all for the comments.

I discussed these issues more with the client and they seem open to slotting these holes thankfully. The anchors are Gr 105 so they are not weldable, but we could use washers and weld those to the base plates. I am hoping that will be the solution, but if not you all have given me good guidance.

 

[dik]

Thanks...

 

[driftLimiter]

SikaGrout 212?

Not sure about Sikagrout. My experience was with Hilti re 500 v3 epoxy. Hilti was about to provide recommendations for capacity adjust for a much smaller annular gap than 3". It was about a max of 3/4" diameter hole for 1/2" anchors.

 

[Greenalleycat]

Sika 212 would work I think - that's a more appropriate product than RE500 at that size
It's rated for rock anchors and can handle up to 80mm (~3") layer thicknesses so it seems about right
I just poured a bag of it into a VERY high flow drain on my property (patching a missing chunk) and, despite my atrocious install, it seems to be holding well

 

[Tomfh]

Yes for big holes you dont use anchor epoxy such as Hilti 500v3. You use a self consolidating pourable epoxy mortar, or a cementitious grout product like mentioned above

 

[driftLimiter]

So now Im curious about the epoxy mortar solution. Lets say you core 3" diam hole and then set an anchor in there with Sika212. Does that provide equal strength to a cast in anchor now?

On a previous anchor repair project I was asked to justify that the grout develops sufficient interface strength to the concrete and couldn't really figure out a sound justification. So I went with the epoxy resin and threaded inserts.

How do we know that the anchor isn't going to pull out as a plug of epoxy mortar 3" diameter?