Elevated Support for Compressor

[Structures33]

Hey all - I have searched the threads and did find a good one (thread256-237000) that discusses compressor foundations. However, my question is regarding an elevated support for 4 process blowers. The compressors are about 76 kips each and the plan (another engineers' design) is to place them on an elevated 12" concrete floor slab. There will also be an additional 6" pad on tope of the floor slab (approx dimensions of 6" pad 22.5'x12') The floor slab is supported by concrete beams and columns that are also supporting the building. i.e. the support system is not isolated from the building.
I have three immediate concerns - 1. the the support is not substantial enough to absorb and dampen the vibration 2. it is not independent of the building framing and 3. adequate anchorage of the compressor may not be possible.
Thoughts/recommendations on this issue are greatly appreciated.

 

[kslee1000]

Common scene in pumping stations. Go out there, have a feel yourself. Also note, except for strength concerns, the constant vibration, or kicks, does not possess a big problem for most of industrial settings, since there are very few people around with long period of exposures.

 

[kslee1000]

Check with equipment supplier on installation of mechanical dampers, vibration absorbers..etc. Check range of operating frequencies against fundamental frequency.

 

[Structures33]

The rep seems to think that it will be ok because he has seen a couple of them done this way before. However, I have 5 different publications (from 5 different sources) that say that the support of the compressor should be independent of other framing. Nowhere in writing can I find that it is ok to have it supported by the building framing system. The installation manual for this unit says the support should be independent but the rep told me that they are revising the manual... not sure if that means they will revise that part.

 

[kslee1000]

It would be interesting to know how they perceived to seperate the equipment from an elevated structure when they suggested it. Figure out the viability of dampers, obsorbers, as it is cheaper and more efficient - eliminate the source of headaches.

 

[kslee1000]

Another suggestion is to talk to the original designer to check out his thinking, and reference materials, over your concerns. If it is done by your company, figure out the designs with similar features that done previously.

 

[Structures33]

kslee1000 - Thanks for the responses. The design was completed by another firm and I do not have the ability to contact the original engineer. I have read that where compressor foundations are supported by floor beams that vibration damping material should be installed between the foundation and the beams. In this case, this would allow for only 6" of foundation for the compressor - not even thick enough for anchorage. Even without worrying about vibration, we would definitely need to increase the foundation thickness to allow for adequate anchorage.
Where do you suggest installing the dampers?

 

[kslee1000]

Your foundation for this case should be 12"+6"=18", tie them together by reinforcing cage. 6" independent pad is out of the question, it won't work. You can provide groove and sealant around the 6" pad and the slab interface to minimize the potential for propagation of cracks from pad to the floor top face.

Mechanical equipment usually comes on skid, on which the dampers and the compressor are attached to. Also, you may design the anchorage to accept damping material of some sort (nut-square washer-damping material-concrete). The former is preferred over the latter.

Talk/write to the designer, he has an obligation to answer those questions, and the right to defend his design.

 

[sundale]

I would isolate these on a separate structure from the building and I would not put too much stock in what a salesman tells you.

The anchorage should not be a problem unless there is some huge unbalanced force. It that is the case, then you have that problem and a few more...

A dynamic analysis is required. Perhaps some seismic dampers might work? Looks like a FUN design problem (really).

 

[Structures33]

kslee1000 - The compressor is sitting on top of a concrete beam. How do I prevent the vibrations from reaching the beam? Are you suggesting that the damping material directly under the compressor has enough vibration absorption to prevent the vibration from affecting the beam and floor?

How do I calculate the natural frequency of the concrete support?

While I can't talk to the designer, I am not trying to criticize - I'm trying to make what they have work. There are a lot of ways to go about this so I'm trying to give them the benefit of the doubt.

 

[kslee1000]

If the proper damper/obsorber were used, the structure below only feels the thrust and uplift (a static problem), if any, exerted by the compressor.

Otherwise, without such devices, you will need the help from a person knows how to model the structure, and perform dynamic analysis on it.