compressor skid reactions 3

[WARose]

Hello. I’ve got some reactions from a compressor mounted on a skid. I’m using pretensioned anchor bolts to “pinch” the skid and take care of the unbalanced forces. One thing I was wondering though: on a day to day basis, there are some shears at the support points he modeled. (He basically modeled the skid with the anchor bolt locations as the support points.....but in actuality the skid has continuous support on a concrete pedestal.) So should I basically take on the shear on a support by support basis, or should I consider the fact that the sum of the forces under operating conditions is zero [putting aside lateral forces and unbalanced loads] and just go with “pinching” the frame for unbalanced forces only (unless the shear from the lateral forces exceeds the [overall] frictional resistance of the skid on the concrete)?

Thanks in advance for any insight.

 

[dhengr]

WARose:
Don’t consider friction for any reaction on a piece of moving equipment like that, a compressor and skids. I’m not quite sure what “pinch” the skid means. You probably have some discrete locations where the skid is supported with your anchor bolts (A.B’s.). Why not consider putting bearing plates in/on the conc. slab at these locations, drilled for the A.B’s., acting as their template. Put some shear lugs on the underside of these bearing plates and down into the conc. slab. Make the bearing plates larger than the flange on the skid, so once you have the A.B’s. locked down you can weld some shear blocks alongside the flanges to take the lateral loads. Using the A.B’s. to take both vibrating tension and lateral loads (shears) is asking a lot. At a later time, the A.B’s. can be loosened and the skid and compressor lifted off. Then the shear lugs can be burned off and the bearing plates cleaned up. And, you may not want the skid resting continuously on the conc. slab or you’ll never get done shimming it, and re-shimming it, as most of the shims loosen, since they are not under A.B’s.

 

[WARose]

Thanks dhengr. When I say "pinch" the skid I refer here to the anchor bolts I will use. They are adjustable cylinders (Rowans) that have to be torqued down to a % of their yield. I'm just wondering about how to treat the vendor's reactions (for forces other than unbalanced).

 

[dcarr82775]

I think the typical design for skid foundations is to use friction to transfer the shears. My understanding is that this is because the anchor bolts are tensioned so they are always in compression, and the space between the foundation and skid is pretty carefully grouted solid.

 

[WARose]

Correct dcarr, that's what I am doing. I'm just a bit unsure as to what reactions to consider here.

 

[paddingtongreen]

WARose, you don't say whether you are grouting the skid, if yes, the vertical load can be linear along the skid. if you are grouting the skid and torquing the bolts, you can distribute the shears along the contact interface. If you are not grouting, place all the shears on the bolts.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[WARose]

Oh yeah, the skid will be grouted underneath.