Floor Vibration 1

[haynewp]

I am modeling a composite steel floor with RAM. For those who are experienced with this software, or vibration in general, I am getting an output of "upper half of slightly perceptible" for almost every beam, even if I make them larger. I am also getting "distinctly perceptible" messages on beams that are located around openings, and I am finding it very hard to get below the distinct range around such openings.
I am wondering if this sounds typical or not. Is the upper half of the slightly perceptible range still ok, or should I consider other means to change the frequency of this floor?

 

[JAE]

We have RAM and have used its vibration system in the past - Also used the SJI program "Vibrate" and both will feel like you're stuck at times. This could be due to your system:

What concrete thickness and damping are you using? Most times the deck thickness (mass) has a much greater effect than adding stiffness to the beams. We get an actual frequency/amplitude plot in Vibrate and as you add stiffness, you essentially just slide down the curve and never get anywhere with added stiffness. The amplitude diminishes with the stiffness, but the frequency goes up and the human response stays the same.

Try adding deck weight and if you have partitions you could include a higher level of damping.

 

[haynewp]

I am using 3 1/4" LW topping and 2" comp. deck. I was counting on a damping of 0.03. LL is 100psf and SDL=5psf.
I've got W14x22's (30' long at 7.5' o.c.) W30x108's (45' long).
I researched all this on my own yesterday, and it appears that the way RAM calculates vibration is not the most up to date method. I don't believe it is checking by the 97 AISC criteria. I downloaded the parametric bay studies program from AISC, and the typical bay seems to work which kind of surprised me, but I am sure it is just barely under the 0.5%acc limit w/ 0.03 damping. Risa floor does use the AISC criteria, though it seems buggy to me at this stage. I agree with you, increasing the beam size helps some, but very little. (I am already being hammered on the weight of this floor.)Partitions are sporadic, there will be floor tables, etc. (it is a laboratory).

 

[JAE]

If it's a laboratory then vibrations may be even more critical. Perhaps you raise the mass in the lab areas only?

Or - there are mechanical dampers that you can include...but $$$???

 

[haynewp]

I have been told from the beginning from the Arch. that it would be designed as a typical office building even though it is a lab. (Must not be sensitive lab work involved). I just confirmed from him again, but I am also trying to get something in writing from the owners on this.

 

[Focht3]

Get that in writing!

If the lab will use electronic scales, then vibrations can be an issue. Same goes for electron microscopes and high resolution scanners. Some laser equipment can be sensitive to vibration.

What kind of lab? You need to know -