Grout under base plates - residential house

[kaspor]

Hello

I have some 270mm (W) x 90mm (L) 10mm (thick) base plates welded onto some SHS columns which will be used to support the upper storey of my house. The slab has been poured a month ago.

Upper storey is tin roof with light weight foam board/render on the external walls.

The engineer has specified 20mm non shrink grout under the base plates, but in every house I've seen built (I've seen a fair amount), never have I seen 20mm of grout installed underneath column base plates. maybe under base plates installed with large heavy loads (i.e. industrial or commercial sectors), but not residential.

Is this an overkill for residential design? Grouting underneath these columns is going to be a real pain.

 

[phamENG]

Grouting is a method for allowing the column to be plumbed. Shim/brace the column into position and then pack the grout underneath. Once it sets up and cures, you have a nice, level surface for the column loads to go into. So if your slab is perfectly flat or you don't care if the column is out of plumb (which could induce additional bending moments that exceed the capacity of the column), then by all means ignore the design engineer. Those base plates are tiny. Grouting them will be a walk in the park for any builder worth their salt.

 

[XR250]

I agree that grouting is easy and a nice way to ensure that your column caps are at the correct height. That being said, I rarely see it done in residential projects.

 

[Aesur]

I typically specify the grout on every project (commercial and residential) for the reasons stated above, however I would not be opposed to allowing the column/baseplate be placed on a smooth/plumb surface, especially with lighter loading. For renovations to existing buildings where new columns are supported on existing slabs or footings (lightly loaded) it is common to place the base plate directly on the surface without the grout pad, however if it's not smooth/plumb then grout should be considered.

 

[kaspor]

Thanks for the responses. I'm really reluctant to grout. If the slab is not perfectly smooth meaning the column may be out of plumb, can I shim underneath it?

I can see in the engineers comps, total dead load = 2.9kPA and total live load = 1.5kPA. This would equate to a total load of 4.4kPA (or 440kg/m2?), meaning the shim would need to be rated for >440kg of load?

I can get shims rated for load up to 20 tonnes. These are more than suitable to correct?

 

[structSU10]

Shims will make the baseplate 'span' in a way it may not have been designed for - which may or may not be OK. The grout is basically a shim that is controllable to ensure contact over the entire base plate surface so it is fully supported.

 

[phamENG]

You'll have to take it up with the design engineer. Only he/she can authorize changes to the design. As structSU10 points out, using steel shims in lieu of grout changes the way the base plate is supported. None of us can say with certainty if that is okay or not. And even if you post the drawings, I'm pretty sure none of us are going to do a free analysis for you.