Dampening Structural Vibrations--Good Books?

[hardyworld]

Problem:
New equipment was recently added to a production plant. This causes noticeable (but not structurally worrisome) vibration in the concrete floor. This issue is that the basement is used for offices, and the noise from the vibrating concrete floor/columns (caused by the equipment) is deafening loud. Preferably, this would be addressed by using appropriate dampening pads.

I do not have any good books on the subject, but I am looking for one.

Does anyone know of a book they'd recommend to solve the above problem (and others like it)?

 

[dougantholz]

You might look to make sure the machine is working properly. This happens quite a bit in hotels with the big washing machines and long period 10 story buildings.

 

[hardyworld]

The machine is definitely running properly. We were aware of of the vibration caused before ordering the equipment.

 

[hardyworld]

bump

 

[JKStruct]

You probably need to isolate the equipment from the floor.. springs possibly. Does the manufacturer of the equipment have any recommendations?

Talk to a rep from Gerb or Mason -- check out the companies online -- they specialize in this sort of thing.

 

[hotgas]

Look in the US Army Corp of Engineer library. See

http://www.usace.army.mil/library/pubserv.html

Years ago they had a technical manual on designing foundations for vibrating equipment.

 

[lutein]

I don't have any books for the problem, but I had to deal with the same problem before, by using 2 books:
[1] Birkhauser, "Vibration Problems In Structures - Practical Guidelines"

[2]Chopra, "Dynamics of Structure"

The easiest way to resolve this is to set the machine on grade. Typical manufacturer requires the supporting foundation pad to be 2x or 3x mass of machine.

It is my understanding that your machine is bearing on elevated concrete slab supported off columns.
For life safety concern, the forcing frequency of the machine should be at least 2x LESS than the 1st mode natural frequency of the horizontal structure. Otherwise, you need to either: 1) stiffen the floor to achieve higher natural frequency 2) machine to bear on steel frames supported on springs. Springs to be designed to absorb the energy imposed by the machine vibration. We have to hire a vibration consultant to design the springs. The springs will reduce the forcing frequency applied to the slab.

Certainly, you still need to design the structure for amplified forces after reduction due springs. See Figure 3.5.1 in Chopra's book for coefficient to amplify the load due to forcing frequenct/natural frequency. By the figure, as your forcing frequecncy from the machine approaches the natural frequency, the forces shall be multiplied by a coefficient of almost infinity, i.e. structural will fail.

Hope this helps.

 

[271828]

Get w/ the equipment mfr and get them to design *isolators* for their equipment.

 

[271828]

...and not to sound mean, but it's "damp" not "dampen." We're not applying moisture.

 

[gwynn]

The book I have used before is "Design of Seismic Isolated Structures: From Theory to Practice" by Farzad Naeim and James M. Kelly. Even though geared at seismic design, the same principles apply. I haven't even flipped through it recently so I can't remember how good a text it is. I'll bring it home Monday for another look.

Lutien
The structure will not neccesarily fail. The factor only aproaches infinity for undamped structures. Buildings typically have on the order of 2-5% damping without any extra measures being taken.

You may also get away with a forcing function many times higher than the fundamental building frequency if there is low participation from the higher modes.

 

[UcfSE]

Look into vibration absorbers as well. You may be able to design and attach a little absorber to the machine. This will vibrate instead of the machine.

 

[VibeAC]

I'm a consultant that deals with vibrations, structural dynamics and acoustics for buildings everyday.

It is very difficult to get a sense of the problem without seeing it first-hand and taking some measurements. Typically bothersome vibrations are due to vertical excitation of the floor, and not horizontal vibration of the entire building, which respond at low-frequencies (typically below 5Hz for the first few modes).

Depending on the size (HP) and the type of equipment, equipment bases (concrete or steel) and vibration isolators (springs or neoprene pad/mounts) can work very well.

Mason is a good company, but they typically do not specify the type of system to be used. I would recommend that you hire an experienced vibration consultant to evaluate the problem; often steps in the wrong direction can create big headaches.

 

[slickdeals]

@271828,
"Dampen" indeed is a word that can be used in this context, and does not always mean to "apply moisture" or make it damp. Dampen means to deaden or to reduce in amplitude.

I am not trying to start a war here, but just stating the facts.

http://dictionary.reference.com/browse/dampen

 

[slickdeals]

I must however add that "Dampening" is not a right word and does indeed refer to making something moist. I must apologize for my oversight on the use of word "dampening", in lieu of "dampen"

 

[VibeAC]

Books you should consider looking at if you haven't already are:

(1) Harris' Shock and Vibration Handbook (any edition) - by Cyril M. Harris and Allan G. Piersol

(2) A Practical Guide to Noise and Vibration Control for HVAC Systems - by Mark E. Schaffer

(3) Noise and Vibration Control - By Leo L. Beranek

There are many other books in this area, but this should give a start.

Andrew Gorton, MSc
Noise & Vibration Consultant

http://www.PapadimosGroup.com

 

[271828]

It's ok SD and is not a big deal either way--no offense taken.

I just don't think I've ever read "dampen" in the literally hundreds of vibe papers I've read. The real vibe guys never use that term. It's not as bad as "cement" vs "concrete" but I'll go with the experts.

 

[VibeAC]

For instance one would say: "I'm going to add a tuned mass to damp the vibration of the exhaust system." or "I'm going to treat the metal panel with a damping material."

Andrew Gorton, MSc
Noise & Vibration Consultant

http://www.PapadimosGroup.com