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Re: concrete vibrational analysis

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terrence turner wrote:
> I am presently designing the floor system for a health/areobics club.  My
> question deals with the following,  how do you calculate the frequency of
> vibration for a concrete flat slab with drop panels?  I have seen alot of
> publications dealing with vibrational problems for steel but rarely for
> concrete.  Any help would be much appreciated.
> thanks
> Jon Turner

This is a bridge engineer's opinion on a building issue.

The dynamic effect of loads is influenced by the mass and the stiffness
of the structure. The bigger the mass and the more flexible the
structure, the less dynamic effects will be felt by the structure.

Even though the stiffness of the concrete floor should be significant, I
would believe that the mass of the floor would dampen most of the
dynamic effects. If the live load capacity of the floor is as per code
requirements, my gut feeling would be that there would not be any

As far as the natural frequency of the floor is concerned, I am assuming
that you are concerned about the floor going into resonnance with the
people jumping up and down. For what this is worth, I never heard any
stories about this happening. I would suspect it is not a problem.

Maybe the reason why you did not find any documentation on the dynamics
of concrete floor is that it is not a problem.

If you really want to calculate the natural frequency, I would suggest
the basic formula w=(sqrt(k/m)) where w=2x3.14xfrequency, m=mass of
floor and k=stiffness.

In order to get the stiffness, I would apply a unit load to a plate and
verify what the deflection is. You might want to consider the stiffness
of the drop panels by reducing the size of your plate. 

The mass would be the mass of the plate (in slugs not in pounds).

Make sure all units are consistent if using this formula.

Bruno Côté