Ground bearing slab vibration

[Ozy101]

Hi everybody!

Just a quick question to see if anyone has came across a similar problem. We are currently working on a research facility where the client has given a set of vibration parameters for the ground bearing slab (very sensitive equipment). I have carried out response factor checks on suspended floors but I don’t even have a clue as to where to start on a ground bearing slab. Can anyone point me in the right direction? I'm not convinced to be honest but inexperience is no excuse for ignorance. Thanks in advance for the time!

Cheers.

 

[JoshPlumSE]

You might take a look at ACI 351.3R. I think it is more concerned with vibrating equipment than vibration sensitive equipment. But, it should be useful at least for establishing the stiffness and damping characteristics of the soil.

Also, AISC DG-11 (which it sounds like you are familiar with) has a good chapter on vibration sensitive equipment. Obviously, it concerned with elevated steel structures. But, it probably still has some good pointers.

 

[WARose]

Before you evaluate the response…..you need to figure what the forcing function is. Is it unbalanced forces from machinery? Human movement? Equipment on the ground level (i.e. forklifts)?

That’s a critical first step. The next one is to get the geotechnical info (spring constants, damping info, etc.).

Once you put those items together, then you can find out what you need. (Since they have given you the performance criteria.)

 

[TDIengineer]

How large is the area of sensitive equipment? I believe I have seen isolation slabs designed for a portion of the building to be vibration free. I would look into that. There is significant cost associated. I am not certain how they do it, possibly an isolation base beneath a thick concrete slab.

 

[GeoPaveTraffic]

From what I've worked on in the past, HVAC equipment is one of the worst drivers for vibrations. Another one that I got involved with was affected by truck traffic from outside the building.

A vibration survey of the site prior to construction might be in order.

All of this depends on just how sensitive the equipment is. Don't forget that vibrations at different fequencies can travel different distances. Truck traffic is generally a low frequency and travel quite far; HVAC tends to be around 60 hz (and harmonics) and generally gets damped pretty quick by soil.

Mike Lambert