Vibration Characteristics/Analysis of Concrete Structures 2

[Formwork]

Can anyone direct me to a good resource on how to calculate the vibration of a concrete structure under service loads?  More specifically, I need to determine how much a concrete structure (one-way joist system; 20" deep joists, 4.75" slab) will vibrate for a hospital project that will be utilizing very sensitve operating equipment.  I have the 1999 ASHRAE Applications Handbook showing various frequency curves.  But what I am trying to determine is how stiff to make the structure.  Any ideas on where to go from here?

 

[Ron]

A couple of suggestions....<br><br>Two good reference sources on vibrations of the sort you are considering are:<br><br>Vibration Problems in Engineering, 5th Ed., Weaver, Timoshenko, and Young,...and<br><br>a book on building vibrations written by Hall, Richart, and Woods (I no longer have copy and don't remember the title but these guys are experts)<br><br>If you have an opportunity to test an existing condition, I would do so.&nbsp;&nbsp;The cost of testing is not that much compared to the data you can gain.&nbsp;&nbsp;Look closely at the tolerances the manufacturer of the equipment provides.&nbsp;&nbsp;Often they are stated in obtuse fashion and difficult to interpret true requirements relative to a building structure.&nbsp;&nbsp;As a safety factor, consider isolation mounts even if not truly indicated by calcs.<br><br>Be careful of resonance.&nbsp;&nbsp;Buildings are prone to this and changing the stiffness of the building structure in different locations will sometimes help prevent this, particularly if induced by rotating mechanical equipment in the building and mounted to its frame (HVAC equip).<br><br>Good luck!

 

[Formwork]

Ron,<br><br>Thank you for the references.&nbsp;&nbsp;I will look them up.&nbsp;&nbsp;Your comment on resonance is worth noting.&nbsp;&nbsp;Testing an existing structure sounds a bit complicated, but it may prove useful.&nbsp;&nbsp;Thanks again.

 

[legner]

See also PCI Design Handbook, 4th Edition, section 9.7 Vibration in Concrete Structures. It provides a hand-grenade method and a list of 11 references.<br>

 

[WIM32]

You could use a FEM program to do some modal analysis and the attain the harmonic response of the building from service loads. A FEM program such as Ansys could be used.<br>Besides that, if the building consists solely of joists and slabs, the following book may be of use:<br>&quot;Formulas for natural frequency and mode shape&quot; by Blevins<br><br>good luck