Maximum cement grout thickness beneath the base plate 1

[ThingsLearner]

I am working at the site of an 8-story steel structure (moment resisting frame). The structure is located in a highly active seismic zone in CA. The construction of the mat foundation has been finished. The base plates have been placed and leveled and now they want to install the columns of the 1st floor (16" box cross-section, 1.125" thick).

For some of base plates, there is 3" to 4" clearance between the bottom of the plate and the foundation surface. They have used regular cement grout underneath these base plates.

I had previously seen up to 2" gap beneath base plates where cement-based grout was used. Isn't there any problem with using cement grout with 3 to 4 inches of thickness? Shouldn't they use pea gravel in the grout? If you see problem, how should we fix it? Is there any way to reinforce the grout? what is the cheapest remedy if necessary?

I appreciate your help.

 

[kelowna]

First thing check the applicable standard. Some of them also have limits. If you are out, you are out.

Second, check the datasheet for the specific grout brand used. It should contain the minimum and maximum thickness allowed. It varies by grout and manufacturer. If you are within the allowable limits you might be OK. If you are out, you know you are not and it gives you an argument to fight for a remedial action.

Some remedial actions might include changing to a different kind of grout that allows larger gaps, adding fibers to the grout mix to reduce or control cracking or reducing the gap by adding steel shim plates.

 

[Stillerz]

are there shear lugs on the baseplates?

 

[ThingsLearner]

Thanks for your responses.

I could not find the specific thickness in the manufacturer instructions. There are some general guidlines saying if you want to use any grout at large thicknesses you should make sure that its properties are suitable for your application!! I called them and they say 4" is too thick and their engineer did not want to advise any remedy directly. I asked him to send me a document showing the maximum thickness and he said he would call me back.

Question: Can we use 2"-thick shims? Isn't it too thick/expensive? If it's ok, how we go about placing them? right beneath the base plate? I am asking about shims because manufacturer said there is no guarantee for fiber reinforced grout and the shims are more conservative. I just got curious what kind of tests do you perform to check the quality of your reinforced grout? just compression and shrinkage? and then do we have any criteria for 4"-thick grout?

There are anchor bolts but no shear lugs.

Sorry for many questions I have but I am not experienced. Thank you.

 

[kelowna]

Shim plates seem the best solution to me. They are not too expensive, quick to fabricate, easy to place and they work well on the situation you have.

They should be the same dimensions as the base plate above. They shoul be placed right below the base plate (make sure the anchor bolts are long enough). No connection between the plates is required. I would grout the gap with the shims and column in place to ensure the column ends up vertical.

Make sure the Engineer of Record approves the remedial action and that the shim plates are properly coated.