Modifications to wall attachments with adhesive anchors

#1

I have a couple sites where wall attachments need upgrades. In some cases the threaded rods would need to be replaced with larger diameter rods and/or deeper embedment.

Is it possible to reuse the holes in order to limit the number of building penetrations? I’m just thinking this would be difficult to remove the bonded anchor, re-drill the hole by the next size up, and then reapply the adhesive. Is reuse a possibility?

If reuse isn’t a possibility and then anchorage point is lowered on the wall (say by a minimum of 3xhef), is there any point to removing the previous anchor and sealing the hole (grout) other than aesthetics and corrosion?

#2

I normally don’t like re-using anchor locations. Check and see if anchor locations were sound. If the original anchors were adhesive, then it is likely they were drilled 1/8" larger than the fastener. They could be cored 1/4" larger than the original fastener and the new fastener being 1/8" larger than the original would provide the 1/8" oversize as required.

This should function as designed; you might want to check with the fastener supplier. If they were expansion type anchors, I would not re-use the locations.

Eg. If original fastener was 1/4" dia, then hole likely 3/8" dia. New hole is 1/2 dia. and new fastener is 3/8" dia. This should work.

Dik

#3

Dik…, you took the words right out of my mouth, off my keyboard.

Why not reuse the anchors which you can, assuming they are in good condition, then add new anchors to make up the difference? This will minimize the total number of anchors and old holes which might have to be repaired. If you are attaching something completely new and different, maybe some of the old anchors will not even be usable. The old anchors are probably pretty tough to remove, unless the new hole is large enough so it can be cored out around the old anchor.

#4

@dhengr
I’ve cored small anchors and they come out like a charm. You may have to use an anchor 1/8" dia. larger than the one I used in my example depending on the core dia you can obtain.

Dik

#5

Good to hear there is some experiences here. Reusing the anchors has been a thought since I usually need 4 instead of the (in-place) 2. Cut a new plate and drill some new holes. The only problem is that some anchors weren’t specified as B7 steel (ductile) which is needed for seismic performance. I’m not saying they aren’t ductile steel, but the grade wasn’t specified (so they could be A307 or whatever threaded rod the contractor had).

#6

I’d be really careful about using anchors for seismic loading.

You cannot rely on the length for developing elongation unless you provide a ‘sleeve’ or something at the top and failure at the thread may be a ‘brittle’ failure.

A ductile failure may be a problem.

Dik

#7

While I agree, adhesive anchors are a decent solution for non-structural components attaching to a building. Some are approved for seismic load, and I find if you take a capacity design approach you can help ensure a good cushion based on the calculated seismic load for the component. What happens during the big shake, I think you can predict but never know for sure.

EDIT: I like thru-bolts way better, but building owners don’t like seeing full penetrations in the envelope.

#8

It’s funny that this conversation happened about a week ago. This week I’m taking the ACI Anchorage in Concrete course and it is really helping to solidify the Annex D concepts — adhesive anchor installation and variables that affect the performance of adhesives, especially.