I assume that you're referring to the shim "stacks" that they use to set the base plate elevations. It will mimic the thickness of grout bed specified +/- construction tolerances. I don't know of a rule but I've typically seen it specified in the range of 25mm to 50mm with the thicker beds being used under more important base plates (braced columns etc.). If I've got a base plate that I consider critical, I'll go with a thicker grout bed and specify a flowable grout instead of dry pack. Sometimes you need access holes through the base plate.
Really, I hate shim stacks all around. They give me the heebee-jeebees. I have a hard time imagining that method results in a clean, uniform bearing surface. In the past, when I've worked in other markets (US), we used levelling plates instead. I like it much better. I'll still specify that from time to time depending on the importance of the connection.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
[blue]Section 2.9.3 states: “Column erection on steel shim stacks is a traditional method for setting base plate elevations that has the advantage that all compression is transferred from
the base plate to the foundation without involving anchor rods. Steel shim packs approximately 4 in. wide are set at the four edges of the base plate. The areas of the shim stacks are
typically large enough to carry substantial dead load prior to grouting of the base plate.”
[/blue]
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Nice reference JAE. In my market, there always seems to be a single pack located at the centre of the base plate. It's permanent. When four are used at the perimeter, are they meant to be temporary by any chance? It's hard to imagine that one would be able to pull them out.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
I've seen typically shims at each corner to allow them to plumb the column. generally they are about 1"x1"so they can fit under the baseplate completely without impacting the anchors.
We have always used stacks of approx 4" square shims at the middle of each side. We push them in a bit to be more directly under the column member and so the grout covers and seals over them.
