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effects of access floor on vibration
i am currently designing a 9-story tower that has 18" access floor on every elevated floor slab because of major electrical requirements. the structure type is composite steel framing. my question is when designing the structural for vibration per design guide #11, can you include some sort of reduction in the vibration of the slab (other than the increase in dl)? it seems logical that access floor would help to mitigate floor vibration, but i'm not sure if research has been done in the matter to produce quantifiable, usable results for calculations. any help you can provide is greatly appreciated.
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steellion,
i would expect this to provide both additional damping and additional dead weight which will both reduce the vibration. the specifics of the damping i am not sure of.
agree with csd72; however, keep in mind that, depending on the construction method, an access floor can actually amplify sound, thus increase some spectra of vibration. make sure that in the process of the structural design you don't shoot yourself in the foot with a bad sound transmission classification (stc) or impact insulation classification (iic) that will result in complaints later.
the access floor will provide some damping due to additional dead load, but will not increase the stiffness of the floor system, which is what you need for vibration control.
additional dl mass doesn't always decrease accelerations. the acceleration is a function of the mass, but it's also a function of the natural frequency (which is also a function of the mass). there are occasions where increasing the mass will increase accelerations - depending how the masses and frequencies play out.

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