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Composite structure nat'l frequency
[Subject Prev][Subject Next][Thread Prev][Thread Next] To: "Struct EngAssoc" <seaint(nospamat)seaint.org>
 Subject: Composite structure nat'l frequency
 From: "ASC" <ggg(nospamat)bigpond.net.au>
 Date: Mon, 12 Jun 2006 21:09:23 +1000
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(nospamat)venturaengineering.com] Sent: Sun 6/11/2006 11:24 AM To: seaint(nospamat)seaint.org Subject: Natural Frequency of a Noncomposite Floor System =20 =20 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. =20 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 =20 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

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