Grout to Transfer Anchor Shear 2

[Althalus]

This is an age old problem with some solutions already used. But I haven't seen any questions regarding this particular method. And I'm wondering what objections there would be to using this method.

1) We have a particular structure that has bad tolerances for placement of anchor holes in baseplates.
2) The anchors are so far apart that placement of the anchors also has bad tolerance.
3) We end up using anchor holes that have 1.5" to 2" of play.
4) we currently use VERY thick and very large plate washers, welded to the baseplate in the field.
5) We're trying to avoid field welding.

Suggestion.

Why can't we have these HUGE holes, set the structure, and fill in the holes with flowable high strength grout?

Any problems with that? How is it different than a shear lug in a grout pocket, or a column embedded in a grout pocket.

Compare any objections with the fact that AISC DG-1 states that we can use friction on the grout pad to transfer shear.

 

[canwesteng]

The objection to field welding is usually well founded, but considering these are flat welds at grade, I don't think the cost is that high. You also need the thick base plates anyway for uplift. I'd have no objection to your method otherwise.

 

[r13]

Why can't we have these HUGE holes, set the structure, and fill in the holes with flowable high strength grout?

What is the grout strength that would satisfy bolt bearing?

 

[Althalus]

R13,

That is a reasonable question. I thought of that and came up with two things.

1) Our current load is 11.7kips of shear with a 1" anchor x 1.5" plate. Many grouts tend to be around the 9 ksi range. That appears to work.
2) How is it different than an anchor in concrete?

 

[KootK]

Why can't we have these HUGE holes, set the structure, and fill in the holes with flowable high strength grout?

I also feel that you probably can do this. You might look around a bit within the precast world as they sometimes use connections that are similar. One issue that may need resolution is that you have to ensure that the anchor won't pull a plug of grout out of the grouted hole under load. Something like a corrugated sleeve, especially if backed by testing, might be an appealing option.

 

[STrctPono]

2) How is it different than an anchor in concrete?

In my industry non-shrink leveling grout lasts about 10 years and then cracks to hell. Not sure what your structure is but my issue with your proposal is the questionable durability of the grout in the long term if exposed to vibration or cyclic loads. If the grout fails inside the HUGE holes, then what supports your anchor bolts?

 

[r13]

2) How is it different than an anchor in concrete?

Quite honestly, I've never seen it done - grout/concrete the over sized bolt hole. It (the hole) is either left open, or plug weld (rarely done also).

 

[Althalus]

In my industry non-shrink leveling grout lasts about 10 years and then cracks to hell.

That is certainly a valid concern. I'll have to look at the durability question a little further. I'm not sure how much it will affect overall performance.

If it fails, it means the material will crack. But since it is confined by the concrete below and the plate washer above, the material remains largely intact. I suppose it will have some reduced capacity. But I'm not convinced the reduced capacity will be by very much. It may be more of a deflection issue than a strength issue. But I'm not all that concerned if it remains in the 1/16" to 1/8" range.

Even so, we're back to comparing it with a grout pocket and a shear lug.

 

[Agent666]

For what it's worth, Hilti have a special washer set that they expect you to use to evenly distribute shear to all anchors within a anchor group. You fill the gaps between baseplate and anchor with their epoxy through a small injectable hole.

https://www.hilti.co.nz/c/CLS_FASTE...TESTERS_7135/CLS_OTHER_ACC_TEST_7135/r4930047

This suggests filling the gap with high strength grout or epoxy is effective.

Without doing this you are accepting a 50% reduction to capacity in their Eurocode based approaches. This is primarily due to the anchors taking up the shear unevenly.

 

[ATSE]

If you go the somewhat unconventional route of "fill the gap with epoxy", I suggest not using C1107 non-shrink grout, but instead a moisture tolerant epoxy grout.
Sika and Five Star and Chockfast have a few to choose from.
However, these have disadvantages as well. But for an interior installation (no direct sunlight, no moisture), an epoxy grout has higher strength, bond, and impact resistance.