@Ron247, why would the shim packs need to be removed? In ~25yrs (in the US) I've never seen anyone attempt to remove baseplate shims before grouting, neither for gravity only nor moment resisting baseplates. I cannot even wrap my head around how that is physically possible?
The location of the shim sets the moment arm length. Shims at the outer edge of the compression side can be removed easier than the middle and provide a longer moment arm near where most people I know estimate the final/design arm location is on a baseplate subjected to rotation. Since you are trying to overcome some magnitude of applied moment, by a couple provided by the product of bolt tension force x distance to centroid of compression area, shortening the distance increases the force. Cutting the design distance in half doubles the force. It has to. Look at the video, The shim appears to be in the center. I agree, they are hard to remove, but I mean, they should not be in the middle to start with.
This is the first one I have ever seen where it is in the middle. The presence of the shim in the center triggered these conclusions. This structure is always subject to rotation. If the connection is always in rotation, you do not even need a shim on the tension bolt side, you just need the nuts to be installed above the baseplate. Gravity loads are much less of a problem, but even those have distribution concerns since the shim is less deformable than the grout. In gravity only loading, the tension on the bolts is not affected by shims.
View this connection in the order it is installed, not the final appearance. Some loads get induced that are not removed/reduced later. Difference in deformation potential between the steel and grout comes later, when the grout is installed. E is not the same for example and how densely the grout is installed is a factor. Even if you held the structure so there was no net moment at the baseplate, but there was still gravity load, the final arm location will be somewhat related to the shim since the shim and grout do not deform equally. But this condition is much less of a concern than starting out that way.
Are we correct about what a shim does to the moment arm?
That is also why I asked, if we were correct in that conclusion. I use leveling nuts thus putting some bolts in compression temporarily, grout except at the leveling nuts, lower the leveling nuts when the grout cures and touch up the grout. I have never seen a shim in the middle of a baseplate on a moment baseplate and like you, I have seen many. Now, I have a lot of projects that I was not hired to do inspection of any kind.
Even if grout is added later, the DL forces are still of the same magnitude. Adding grout while the center shim is still there, does not relieve the bearing on the shim. The steel shim will resist deformation more than the grout in most cases. Makes it hard to estimate where the true centroid of the compression area is located.
If I am wrong about this, I would appreciate knowing (mechanically speaking) why I am. As I say below, "Never too old to learn". So, anyone who thinks I am not picturing what is going on correctly, please enlighten me. It will be appreciated. I do not need any more tin-foil hats, no matter how stylish they may be.
In your opinion, is there an error in my mechanics, as opposed to a difference in opinions of the long-term implications? Mechanically, I could use a shorter moment arm in my calcs and therefore allow for any difference. I just know where most people I know estimate the centroid of compression to be approximately.
