Thickness of grout below baseplate? 2

[StructureMan44]

What determines the required thickness of grout below a column baseplate? Do any standards (AISC, ACI, etc.) specify a range based off column load or baseplate size?

 

[Guastavino]

I don't know of a code requirement (although I could be ignorant of one), but I usually specify 2" for typical column base plates. That allows room for leveling nuts and enough space to pack the grout in without voids. If there are actual code provisions, I'd like to be enlightened as well. My thoughts are it's typically based on historical best practices and grout manufacturer recommendations for max thicknesses.

 

[Teguci]

AISC Design Guide 1 - "If the column is set on a finished floor, a 1-in. space may be adequate, while on the top of a footing or pier, normally the space should be 12 in.
to 2 in. Large base plates and plates with shear lugs may require more space." pg 9

 

[KootK]

I've seen base plate details with as little as 3/4" (small, gravity load only) to as high as 4" (industrial columns with moment). It seems to be mostly a judgment thing depending on how critical the application is, and how much tolerance you think you'll need for column pluming etc. Somewhere, I've seen a recommendation regarding the ratio of grout depth to distance between grout access points for big plates where you often provide access holes. For the life of me, however, I can't remember the recommendation or the source.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[mike20793]

I was always taught it's based off anchor rod diameter, so I use 2" thickness up to 2" anchor rods and switch to 3" up to 3" diameter and then go to 4" grout thickness. I have no clue where it was developed, but it my firm's in house "policy".

 

[SAIL3]

I usually use 2" and a min of 2 grout holes in the base pl, especially when using shear keys...

 

[KootK]

First edition AISC design guide advice is first blurb below. The next two blurbs are from the first edition which is, surprisingly, more helpful.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[AnimusVox]

In our office we use 1.5 inches of grout for 3/4" anchor bolts, and 2-2.5 inches for 1"-1.25" anchor bolts; just to allow for enough space beneath the plate for the bolts. A phone call saying there isn't enough room for the plate + leveling nuts (and plate washers if applicable) is not a phone call you want to get. (I once had this happen to a coworker at a previous internship)

 

[structSU10]

We use leveling plates around here a lot, so we usually have 3/4" grout bed below the leveling plate.

 

[mmasoudi]

Hi, I need to know the minimum distance between grout holes in a large pump base plate to avoid air pocket. Is there any standard or guideline?

 

[Tmoose]

Check with the grout manufacturer. I think you will find there will be limits to the maximum thickness. If the grout is too thick the heat generated can cause even more rapid curing that causes issues. Extra stone/aggregate can slow the reaction and help with borderline situations.
Epoxy grout is especially vulnerable.

ACI and API have some pretty specific recommendations.
Rotating machinery is particularly critical. I would NEVER leave leveling nuts on the anchor bolts, since tightening the upper hold down nuts later would not clamp the base against the grout

https://www.concrete.org/committees...acommitteehome.aspx?committee_code=0000351-00

Discussion of clearance Section 5.5
Dry packing is not straightforward at all. Section 9.2 and 7.4.3
Grout filling holes for large bases Section 5.2
Placement discussion 7.4

 

[MacGruber22]

I prefer leveling plates to minimize the grout thickness, as I think structsu10 was getting at. I think the workmanship tends to be much better with leveling plates. I have watched many different contractors dry pack under a base plate that was set with leveling nuts and the quality of grout pack is often suspicious.

Tmoose, I know you are trying to be helpful and I agree with almost all of your statements - but, I don't think it is appropriate on Eng-Tips to post ACI documents that have been illegally downloaded. I recommend editing your post to change the link to the official ACI site so that we may still have your good post.



"It is imperative Cunth doesn't get his hands on those codes."

 

[mitzen]

from OP (What determines the required thickness of grout below a column baseplate?)

Usually companies/projects specify/recommends grout thickness or even have its standard drawings specially if they are doing it again and again. It is better to ask your lead/manager if is provided and stick with it. In our firm we have standards so i tend to follow it.

 

[darthsoilsguy2]

so-called "leveling plates" seem to always have a few with a gap between the plate and the column base plate. i can't see why they ever came around in the first place besides to spend time placing metal shims.

 

[mehranmasoudi]

Thank you Tmoose for the information, would you please advise complete ACI 5.2 address, I can't find "Grout filling holes for large bases Section " ?

 

[shaneelliss]

This is a good resource for grouting information:

http://www.fivestarproducts.com/ind.../?d=0&file=custom/upload/File-1399650344.pdf.

If the link doesn't work, just google "A professional's handbook on grouting and concrete repair".

It is obviously written with a viewpoint that 5-Star branded grouts are the only grouts you should use, but almost everything in this handbook is good grouting advice regardless of the type of grout.

If I remember correctly, it basically says that 2" is the recommended grout height for plates up to 3' wide and to increase this grout height 1" for every additional three feet of width.