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Composite structure nat'l frequency

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A comment on the discussion below:
 
A quick estimate of NF can be obtained as follows:
 
Calculate static deflection under gravity, ust.
 
Circular freq. squared = g/ust
 
where g is accel. of gravity in consistent units.
 
nat'l freq. in Hertz = circular freq./(2pi)
 
Sincerely,
Gregory from Oz
 
 
-----Original Message-----
From: Brian S Bossley [mailto:BSBossley(--nospam--at)venturaengineering.com]
Sent: Sun 6/11/2006 11:24 AM
To: seaint(--nospam--at)seaint.org
Subject: Natural Frequency of a Noncomposite Floor System
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I am trying to calculate the natural frequency of an existing floor =
system and though I've read through the appropriate portions of Design =
Guide 11, I'm still having a little trouble understanding a few things.

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There is a line in the Design Guide that states that the transformed =
section properties are to be used if the deck is attached to the =
supporting beams, regardless of whether or not shear connectors are =
used.  The natural frequency of the beam is then estimated based upon =
the composite beam deflection under dead load and vibration loading.  So =
am I to assume that the full composite section properties (using 1.35x =
Ec, .) should be used in calculating deflection, also?  My software =
package seems to disagree with me on that point, but then it offers no =
explanation as to why not. =20

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I think the actual initial deflection of the beam would be based upon =
the bare beam section for the weight of the beam+slab, and then possibly =
based upon the composite section for the equipment load.  Is it correct =
to look at the actual deflection in considering the natural frequency?  =
If so, wouldn't it be based only on the equipment load, and not on the =
dead load + equipment load?=20