Post-installed Concrete Anchor Bolts and Misplaced Embeds

[muchtolearn]

Some of you may find this to be a dumb question, but I will go ahead and ask...

I have designed embeds for components and cladding anchorage on a large project in a high wind pressure, hurricane-prone region. On projects this large, I find that there are always some locations at which embeds are misplaced or left out of the construction entirely. See the attached sketch for a generic detail of my condition.

At misplaced embeds leading to the need for a post-installed anchor bolt fix, should I be concerned about the spacing between the post-installed anchors and the cast-in-place (embed) anchors? Will the embed anchors create a breakout surface within the concrete substrate that should be considered? Any specific resources that I should be referencing for this type of issue?

Thanks so much for any advice/suggestions.

 

[EngineeringEric]

I would think that the spacing of a CIP and post-installed (say epoxy) would act the same for either application. The concrete does not know how the anchor was installed, it only sees the modes of failure outlines in ACI App.D or other code. Some guys on here have far more knowledge in the matter and may provide additional insight.
-
The diameter of the post-installed should be the drilled hole size, and the emdedments of both should be checked relative to each other (for concrete breakout and such)

 

[JAX91]

I specify a lot of Hilti products. For their anchors approved for use with Appendix D, they provide ICC Evaluation Service Report (ESR Report). These reports give a well defined design method for their anchors. If you read through the reports, the design method is almost identical to Appendix D. There are a couple of variables that are different (kc = 17 in lieu of 24). Also, the concrete pullout is calculated based on the epoxy strength instead of the anchor head size. Ultimately, I don't think the spacing would be calculated any differently. You can download copies of the ESR Reports from Hilti's website at

http://www.us.hilti.com.

Their newest epoxy is Hilti HIT-HY 200. The corresponding ESR report is ESR-3187. You should be able to search for this report on their website.

 

[ztengguy]

I would think that the misplaced CIP anchor would be the same as a piece of rebar there, just something to help keep the concrete together. I would try and get it 2-3 inches away so you dont fracture the concrete between the hole and CIP anchor. Perhaps make the fix bigger, so one side is anchored by the CIP anchor, the other side is a epoxy or mech anchor.

 

[muchtolearn]

Thanks for the replies folks.
I am very familiar with the ESR reports, use them everyday
ztengguy - my opinion/thoughts align pretty much identically with yours, just wanted to see if there were any varying ideas out there.

 

[racookpe1978]

As I recall from analyzing drilled-in/epoxied-anchored Hilti (and their competition) anchor bolts in concrete, the pull-out resistance is a cone centered on the new anchor bolt, extending down into the conrete as deep as the anchor bolt goes. In general, if that cone does not intersect a "open wall" or "open side" of a curb or the edge of the concrete, the anchor bolt/threaded rod can develop its full capacity of the cone both sideways (in shear) and vertically (in tension).

So, your goal should be keeping that 45 degree cone from the tip of the embedded anchor bolt hole to the surface of the concrete away from unused anchor bolts, and most certainly away from used anchor bolts carrying tension!

If the cone intersects an existing (unused, no-added-stress-to-the-concrete!) anchor bolt, then you need to reduce the effectiveness of the "cone" as if it were hitting the edge of the slab or side of a curb. (To be conservative.)

To assume that the interaction "cone" "flows around" or "flows through" an unused anchor bolt as if it were solid untampered, undrilled concrete would require actual pull-out tests rather than assumptions.

 

[ztengguy]

@ racookpe1978, if the cone intersected a headed stud that had no other tension on it, would it not engage that headed stud and add to the area its trying to pull out?