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Re: Vibration design practice for condominiums

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Tom,

I am not aware of any foot traffic vibration requirements in the codes.
But, then I _ALWAYS_ take a look at that as people don't tend to like it
when the floor vibrates just from a lightly loaded cart rolls down the
hall or someone walks down the hall.  I rather not have to deal with a
phone call from a nervous client somewhere down the line wondering why
his/her floors vibrate with someone walks on it.  To me, this is in the
same line of "prudent" engineering as making sure that your high rise
structures period doesn't match that of a human being's internal organs
when the wind blows...people don't seem to like getting nauseous (sp?)
while sitting in their office on the top floor of a high rise building.
Go figure! ;-)

Sound transmition (either audibly or by felt vibrations) is something that
I don't know much about (other than I have had neighbors in appartments
who either had a stereo or electric guitar that bothered me...or other
sounds for that matter, some moderately entertaining).

Regards,

Scott
Ypsilanti, MI


On Tue, 16 Dec 2003, Tom Higgins wrote:

> Colleagues,
>
> This is a question about current practices and design economics in
> relation to floor vibrations and sound transmission in dwelling units.
> In condominium construction, for example, what steps, if any, are
> typically taken in the design of the primary structure to  limit impact
> sound transmission through the floors?  More specifically, if the floor
> structure is a composite concrete slab on metal deck, are any special
> steps ever taken in the design of the floor structure itself, narrowly
> defined?  Is it ever economically justified to add concrete thickness
> and mass to obtain a better IIC rating?  Aren't there almost always
> better (more economical/cost effective) ways?
>
> The UBC and IBC require that floor-ceiling assemblies in dwellings meet
> an impact insulation class (IIC) of 50 (1997 UBC Section1206.3.  See
> also ASTM E 492).  Floor coverings, carpet pads, sheathing on sleepers,
> gypsum board ceilings on resilient channels, fiberglass batts,
> perlite-sand toppings, rubber sheeting, proprietary "floating floors,"
> and all kinds of other materials can apparently be used to help achieve
> a desired IIC rating.  An industry has grown up around this issue, but
> it seems to me that the matter is typically dealt in design through
> architectural specifications.  Do structural engineers really have a
> genuine role in this issue?
>
> As I see it, the code is concerned with **sound** transmission through
> the floor-ceiling assembly.  The issue of harmonic footfall-induced
> vibrations traveling laterally through the floor and causing discomfort
> for occupants seems to be separate.  Investigation of vibrations induced
> by rhythmic footfalls does not seem to be addressed by the codes at all.
>  Investigation of and potentially design to mitigate these vibrations is
> something structural engineers are sometimes called upon to do, but I
> don't believe they typically act except on client's specific
> instruction.  On the subject of sound transmission, though, I have my
> doubts.  Are there any practical steps to be taken?
>
> Well, colleagues, what do you think?
>
> Tom
>
>
> Thomas B. Higgins, P.E., S.E.
>
> Group Mackenzie
> 0690 S.W. Bancroft Street
> Portland, OR 97239-0039
> Phone (503) 224-9560
> Fax (503) 228-1285
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