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Omitting Base Plate Grout

Omitting Base Plate Grout

Omitting Base Plate Grout

(OP)
I have designed a large retail/warehouse store.  Some of the columns support 250k loads.  The same contractor is pouring the footings and going to erect the steel.  He wants to omit the grout.  He states that he is going to pour the footings so smooth that the column baseplate will bear directly on the concrete.  THese are 10'-0"x10'-0" footings.  I do not beleive he can pour the footing to within 1/16" of the proper level.  Also , this Contractor is friends with the Owner, so I am hte outsider.  

Can anyone help to support the case of keeping the grout?  I have read thru Steel Design Guide, 2nd edition.   

RE: Omitting Base Plate Grout

I think this is easy.

-Concrete shrinks more than non-shrink grout. No guarantee of proper bearing.
-Not a chance that concrete will flow as well as grout to fill all voids.

Anyone else got any others?

RE: Omitting Base Plate Grout

I have seen this done in pre-engineered metal buildings in the past.  I questioned the design and was informed that it was to keep bending in the anchor bolts to a minimum (actually makes some sense).

Anyway, how will they finish the concrete that smoothly around the anchor bolts?  I just cannot see how they will be able to ensure full bearing without grout.   

RE: Omitting Base Plate Grout

I would not permit it. There is a good reason that it is a rare procedure, in fact, unique in my experience.

Michael.
Timing has a lot to do with the outcome of a rain dance.

RE: Omitting Base Plate Grout

If omission of grout works, the contractor looks good.

If you allow it and it doesn't work, who looks bad?

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Omitting Base Plate Grout

Any minor irregularity can induce moments in the column.  Incomplete grouting (on no grout) creates hot spots which will either take the full bearing load, or will give way under load and cause redistribution.

The contractor apparently believes that he can not only make the bearing surface flat and level, but also to perfect elevation.  Doing so is so time consuming and unreliable that no one else does it.

I never would permit it for those kinds of loads.

RE: Omitting Base Plate Grout

Ask the contractor to provide a plan of how he is going to float the column in the wet concrete to obtain the full bearing that is required.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Omitting Base Plate Grout

I assume that the contractor will also allow for construction tolerances in the steel frame that will mean that the frame will not need to be shimmed to level it up.

RE: Omitting Base Plate Grout

I would tell him that he can omit the grout if he gets an approved elastomeric bearing pad.  I belive these are used often under bearing for bridges supporting large loads.  But if I had to guess, the elastomeric bearing pad is probably expensive and grouting would be cheaper.  Now if the owner questions you, you can say you gave the contractor an alternative to grouting.  

RE: Omitting Base Plate Grout

I went through the exact same thing once.  Owner's construction manager was irrationally against the concept of grouted base plates.  

We let them do it...  But, we assumed that the bearing only happened at the leveling nuts and designed for a thicker base plate.  In the end it didn't end up being a very big deal.  The base plates were not heavily loaded and this only resulted in a minor change to base plate thickness.  Maybe we added a stiffener to one of the columns or something.  

To me it's a matter of explaining (in a formal letter) that their proposal will likely result in increased steel fabrication costs....

In my case, it also lead to increased corrosion due to possible contact with water.  But, that was at least partially because that same construction manager refused to allow for any slab drainage.   

RE: Omitting Base Plate Grout

High moment foundations such as light poles do not use grout, but bear on leveling nuts. Grout is unnecessary when the bolts/plates are correctly designed to accept the load.

RE: Omitting Base Plate Grout

The OP says bearing on the concrete, not on leveling nuts!

I have used leveling nuts and no grout on poles and substation structures but never on a regular structural column.

Michael.
Timing has a lot to do with the outcome of a rain dance.

RE: Omitting Base Plate Grout

This guy plans to finish the concrete so smooth that he doesn't need grout.  He isn't planning to use leveling nuts.

Omitting grout on minor columns may be okay where the bearing pressure is very small, but it isn't appropriate for loads of 250,000#.  The bearing pressure will not be uniform under the baseplate.

BA

RE: Omitting Base Plate Grout

The Engineer of record controls this. Tell the contractor to find a different engineer willing to take all the responsibility for everything.

Richard A. Cornelius, P.E.
WWW.amlinereast.com

RE: Omitting Base Plate Grout

Sounds like an arrogant contractor trying to impose his know-how over us "dumb" engineers and our pointless methods.

RE: Omitting Base Plate Grout

You could always agree with the contractor.  Then measure each baseplate location - after the conrete is poured.

And require he polish/grind smooth/repour the concrete under each baseplate NOT bubble level both ways, exactly ruler-edge flat, and baby-butt smooth over the entire portion where every baseplate seats.

RE: Omitting Base Plate Grout

Write F(F) and F(L) of something comparable to an industrial warehouse floor (like 120 and 100) into the spec  that he has to hit for the top of footing.   If he can hit them, great.  If not, then the fix is grouting the baseplate.

 

RE: Omitting Base Plate Grout

The contractor cannot plumb his structure when grout under the baseplate is omitted.  The practice of omitting grout is simply unacceptable.

BA

RE: Omitting Base Plate Grout

This is slippery slope time. If you say "Yes.", when it doesn't work and it won't, you will be asked to "buy off" on the eccentric bearing - at your expense since you made it part of your design when you said "Yes" in the first place.

If this sounds extreme, it is not. The people familiar with the circumstances always disappear, along with their memories of events, and then you have to deal with bean counters and lawyers who only look at what is written on the paper.

As I said before, if it was a viable way to build, we would all be doing it.  

Michael.
Timing has a lot to do with the outcome of a rain dance.

RE: Omitting Base Plate Grout

(OP)
Thank you all for your answers.

Currenly, in hte meeting this morning, the owner stated that he did not want the grout after hearing from hte contractor.  The Contractor who is a friend of hte Owner says he does this all the time.

I said I did not agree but offered as a compromise that they had to measure the elevation and levelness of hte first 8 foundations they pour.  They agreed to this.  

I do not beleive they can do this.

RE: Omitting Base Plate Grout

My vote: don't allow it! Sounds like bad news... Plus, like others have said, you are driving the structural ship, never let a contractor take the ropes on these types of details. And I am surprised this is not spelled out in AISC?

You will be involved if there are any problems, and the costs of grouting under the base plates would seem VERY minor compared to the cost of the whole building. Why is the GC taking such a hard stance on what seems to be such a small detail? I am also surprised at his cockiness to his concrete work and steel accuracy, the leveler nuts let you make adjustments to the elevations.

Light poles to not have 250k axial load. Also, the bolts and nuts are designed for this axial load.

 

RE: Omitting Base Plate Grout

You might as well get the client and contractor to sign a waiver/legal document (don't know what it is called) that they've not constructed the building in accordance with your advice or the applicable standard.

RE: Omitting Base Plate Grout

So I'm a little curious here. You are still the EOR, it's your design. I know we work for the owner (or contractor, or architect - whomever the client may be), but if you're  the design professional that is responsible for the completed project then you should be comfortable with every aspect of it.

Where can we as engineers draw the line and say we're not comfortable with that?    

RE: Omitting Base Plate Grout

Doesn't that also violate a standard of care?  I dint know of anyone who doesn't grout base plates.

RE: Omitting Base Plate Grout

One more thing to think about and maybe this would change the owner's mind.  Let's say for a moment that this contractor has the greatest concrete finisher ever and he gets this tip of footing dead on in terms of flatness and levelness.  How will he handle the steel tolerance?  The column isn't going to come out with the base plate perfectly orhthognal to the axis of the column.   

RE: Omitting Base Plate Grout

design professional is responsible for the completed design, not completed project. If you don't believe that, than imagine that the owner had not given you a contract for construction phase engineering. Instead, he decided to hire another cheaper engineer to do that. That engineer would then be in your position to review the contractors RFI's, not you. Would you still be responsible for the missing grout? So unless you agree that it is acceptable, then you are not liable. You should make sure you are on record of not approving anything and not recommending any alternative.

RE: Omitting Base Plate Grout

For lightly loaded columns, the lack of grout would be acceptable.  For columns loaded as you note, they should be grouted.

If not, you may be relying on the plastic action of concrete, crushing until sufficient bearing is achieved... I don't normally design on that basis...

Dik

RE: Omitting Base Plate Grout

The procedure proposed by the contractor may work satisfactorily if his work is as accurate as he claims it is.  Otherwise, he may be called upon to provide remedial measures.  Berniedog should not accept work which is doubtful.

BA

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