Vertical Vessel Skirt/Base Ring on Shims
Vertical Vessel Skirt/Base Ring on Shims
(OP)
In my study of the design of vertical vessels on skirts, base ring sizing appears to be dealt with adequately well, except for one practical consideration: My Civils colleagues want to place shims under the base ring for levelling purposes before flooding with grout and tightening the anchor bolts.
My questions are:
1) how strong is the grout?
2) if the grout is weak, how is load transferred between the base ring and the main concrete slab?
3) should the shims be placed near the bolts or mid-span?
4) how does this affect the base ring design sizing
5) why is this not addressed in the well known design routines?
All constructive comments welcomed.
My questions are:
1) how strong is the grout?
2) if the grout is weak, how is load transferred between the base ring and the main concrete slab?
3) should the shims be placed near the bolts or mid-span?
4) how does this affect the base ring design sizing
5) why is this not addressed in the well known design routines?
All constructive comments welcomed.





RE: Vertical Vessel Skirt/Base Ring on Shims
The grout is not part of the base ring design, nor is the shimming, hence the skirt design assumes full support under the base ring. The rest is the civil engineer's job to ensure the rigid grouting under the base ring for proper support of the vertical vessel. Apart of that, the shims can be removed if located suitably or can be embedded in the grout permanently, at civil's discretion.
cheers,
gr2vessels
RE: Vertical Vessel Skirt/Base Ring on Shims
RE: Vertical Vessel Skirt/Base Ring on Shims
RE: Vertical Vessel Skirt/Base Ring on Shims
In fact, I cannot imagine how it would be possible to set a pressure vessel or other equipment in place without using shims. What will support the equipment the 1" or so off the top of the concrete foundation while grout is poured or packed, then sets up? This is just not possible without a "sky hook".
Most likely, such problems as this are generally left to the people who install the equipment. If the owner is lucky, these people will have some engineers on staff who will assist in developing an erection procedure for large, heavy, costly equipment such as a shop built vessel.
But the question raised is a good one. In the design procedure for skirt base rings on pressure vessels as outlined in numerous texts there is no mention of erection or construction condition where there is no uniform support under the base ring; instead the vessel and base ring likely will be supported at discrete points, likely by steel shims, and likely these shims will be located near the anchor bolt chairs or other gussets to prevent any local buckling of the skirt due to the concentrated load.
It would be a good idea to check the skirt and base ring for such temporary concentrated loads as this. Design guidance for this can be found in the AISC Steel Manual for concentrated loads for beams and plate girders, or in a textbook on structural steel design addressing same issues.
RE: Vertical Vessel Skirt/Base Ring on Shims
Non-shrink grout usually has a higher compressive strength than the concrete. Not sure about a cement-sand grout- it quite likely would.
RE: Vertical Vessel Skirt/Base Ring on Shims
RE: Vertical Vessel Skirt/Base Ring on Shims
Grouting is specified when the vessel has reached a certain height so as not to overstress the base plate and skirt in the shim supported condition.
Shop erected vessels are set on shims as well and then grouted.
Normally, the empty vessel weight (without insulation, platforms, piping, contents) is small enough so that the base plate & skirt are unaffected by this temporary loading condition. Often, this empty weight may only be 15-20% (often less) of the flooded (operating) weight so in the cases I normally work with it isn't an issue.
Typical grout in either case is 5000 psi non-shrink.