Omitting Base Plate Grout 1

[Berniedog]

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.

 

[weab]

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?

 

[OHIOMatt]

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.

 

[paddingtongreen]

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.

 

[MikeHalloran]

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

 

[TXStructural]

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.

 

[msquared48]

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

 

[Grahammachin]

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.

 

[DWHA]

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.

 

[JoshPlumSE]

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.

 

[civilperson]

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.

 

[paddingtongreen]

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.

 

[BAretired]

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

 

[dicksewerrat]

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.

http://WWW.amlinereast.com

 

[VAStrEngr]

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

 

[racookpe1978]

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.

 

[Lion06]

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.

 

[BAretired]

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

BA

 

[paddingtongreen]

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.

 

[Berniedog]

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.