Bolts Chopped Flush, Reuse Existing Holes

I'm in construction, and we're doing a project where the steel frame for a piece of equipment is being replaced. The new equipment shares the same exact bolt pattern (9 bolts), must be installed in the same exact spot, but requires new anchoring hardware.

The existing condition is 1/2" mechanical wedge expansion anchors in concrete, that have been cut off flush with the existing concrete slab.

What we ended up doing was using a combination of punch/hammering and metal drill bits to get the head of the chopped anchor down below the concrete slab level. Then we used these Hilti Rebar Cutter bits to literally grind up the existing bolts and surrounding concrete until we were left with a (now larger) hole. We'll be using Hilti HY-200 and larger threaded rod for the new anchors.

This had me thinking. If someone wanted to replace climbing bolts with the same existing condition, but reuse the existing holes. Is there a better way to do it?

How many bits did it take?

M Mwrote:

How many bits did it take?

Just one bit for the nine (9) anchors. He had 2 bits available, and he told me if he needed to do any more bolts he would have switched to a new bit.

It took a full 8 hour shift, though.

Core drilling.

It is a type of core bit, just carbide teeth and not diamond. A diamond core bit is what I would have used, I think these bits are more meant for crosscutting rebar when you are drilling normal holes in concrete.

One bit in a day is impressive though.

Jim Tittwrote:

Core drilling.

When we proposed core drilling and casting in new anchors, the engineer argued that we would be pulling out on the grout cylinder and not on the entire slab. Pull out force depending entirely on the bond between the grout and the existing slab.

We entertained the idea of using HY-200 instead of grout after we cored a 1” hole. Obviously this would use up a lot of epoxy. But the main issue is that it would fall outside of the HILTI parameters for the thickness of epoxy in the hole.

Is the amount of epoxy relative to the size of the anchor and size of the hole not a big deal when it comes to climbing anchors?

Would the re-bolter need to use a battery powered hand core drill? Or is there another tool that could be used? Perhaps an SDS to core bit adapter?

The core diamond core drills for 12mm bolts leave a ca.16mm hole and we'd glue in a 16mm bolt. Too much gap does start to weaken the placement but even with a smaller (12mm) bolt we are still within the standard requirements.

Wej-it makes these anchors that might have been a good solution. This one is 3/8 thread with 1/2" OD. They make 1/2", 5/8",3/4" and 1" thread versions. I have occasionally used these for climbing. I found the 1/2 hole was really not big enough in hard rock.  9/16 hole would be perfect. They come in 316 SS as well as plated for indoor construction. These are great for installing a machine on not so good concrete, where you might need to move the machine later. Those lugs are not going to pull out of good glue!