Concrete Anchors Damaging Rebar? 1

[Archie264]

Colleagues,

What are your thoughts regarding installing concrete anchors into existing structural concrete? I fight this battle on a frequent basis, that is, I don't like anchors installed in the proximity of tension steel. The pushback I often get is that when a concrete drill hits rebar it rattles the drill operator so he doesn't continue to drill through the rebar. Perhaps, but perhaps also you'd like to purchase a bridge I own in Brooklyn?

Anyway, this is an issue that I have to deal with on an ongoing basis so I'm curious as to your thoughts and how you approach this topic. Thanks.

 

[PicoStruc]

Consider youself already lucky that you don't get involve after they did a boring hole through concentrated rebar in seismic shearwall to pass mechanical vent !, True story !

Seriously, if I understand correctly, the tension rebar is perpendicular to the anchor. So what do you fear ? Removal of concrete around tension bar because of drilling?

 

[Archie264]

No, my concern is damaging the rebar itself. That is, drilling through all or a portion of the rebar. And this becomes more of an issue when many anchors are to be used in a bay. Am I right to be concerned about it or are they right in claiming that it's unlikely to occur because of the extra effort involved to do so?

 

[DDBPE]

The drilling will will not damage the rebar with the typical hammer drill, the bits are not made to go through rebar. They will bounce on the steel and not penetrate and you can usually here the pitch change when you hit the rebar, or in my case one time, the bit hung up beside the rebar and spun the drill around and almost threw me off a bridge (luckily I was tied off with a harness). Hammer drills have high torque.
For concrete with rebar, core drills are used and the core bit has diamond grit to cut the steel.

 

[XR250]

... unless they switch to a rebar cutter bit when they hit the reinforcing.

 

[graybeach]

I generally require that rebar be located before drilling and try to work flexibility into details so things can be moved a little if necessary. If the rebar is in a critical area, has high tension, or when there is prestressing or post-tensioning, I try to avoid drilling. If that's not possible, I make sure an engineer or owner's rep is watching during drilling.

 

[DDBPE]

yes they could switch but would not be able to use the hammer drill, as most cutter bits work with standard 1/2" drills and it could specified not to use a rebar cutter bit of any form.
Hammer drill bits are usually carbid tipped and damage before damaging the rebar.

 

[dcarr82775]

Most of the contractor's I run into don't use the bit that will drill through rebar. They just drill 1000 holes until they find a bit of concrete without any steel. On some projects the owner has required GPR or Xray prior to drilling any concrete because those pesky electricians tend to embed conduits in the slabs and you never quite know where they are. Hitting that with a drill gets a guy's attention.

 

[cvg]

relocation of the anchor is not always possible and location of the steel before design or drilling isn't either. hammer drills are slow and core drilling is much faster, but will cut through the rebar. hitting rebar can cause significant delay, re-work and cost implications. however, I don't know what the solution is. If you need a post installed anchor in a certain spot, there are often few other options.

 

[TXStructural]

As stated, drilling with a hammer drill and standard bit (i.e., 99% of the cases) will not cause a problem. Core drilling should be avoided unless careful consideration is made about location and the purpose of the reinforcement. Core drilling is not appropriate for many types of anchors.

Generally, if placement is critical, it is best to solve that issue. Otherwise, there is so solution but to cut the bar with a core drill and make other arrangements to control tension in the member.

 

[dcarr82775]

Depending on the type of anchor, the use of a core drill may not be compatible with the anchor itself

 

[cvg]

on a recent project, there were literally 100's of 1-1/4 x 16 inch deep drilled epoxy anchors. underwater with no chance of either pre-locating the steel or moving them. drilling with a standard hammer drill would have taken weeks at a cost in the millions. core drill was the contractors recommendation due to the reduced time required to drill all the holes which greatly reduced the cost. the only option was to stop when the drill hit steel and omit the anchor. Additional anchors to make up for these had to be field located.

 

[XR250]

@DDBPE;

http://www.bluetoolking.com/product...oduct-search&gclid=CKmh0-78lbkCFfFj7Aod7HYAOA

Has an SDS shank so it fits a standard hammer drill. Might have to put it on rotation only mode to use it.

 

[DDBPE]

Excel, Thanks, I see the cutter bits work in a hammer drill now, but when I used to do a lot of work with concrete, these type bits were not available to fit the hammer drill, they were originally used with 1/2" drill.

If we hit rebar, we would have to use a core drill if it was allowed, or move the anchor, which in some cases cannot be done.
If we knew where the anchor was to be installed, prior to concrete placement, we would make sure the rebar was not in the way. After placement, we would use Xray to determine a good location for the anchor.