Vibrations 1

[craigory28]

The company I work for has got a lot of work all of the sudden in which we have strict vibration criteria. (V < 2000 microinch / sec.) In order to analyze steel structures I have been using the Steel Design Guide Series 11, &quot;Floor Vibrations.&quot; I am wondering the following:

1. In the manual (pg 48), it states that, &quot;In calulating this deflection, the local deformations of the slab and deck should be neglected, e.g. only the delections of the beams and girders should be considered, taking account of composite action...&quot; In my opinion this does not seem very conservative. With composite construction you could have a beam spacing up to 10', whereas with a concrete system your purlins would be much tighter. It would seem that the concrete would fair much better.

2. Has anyone found a good method to analyze concrete for vibration? I'm looking for something similar to the Steel Design series but in concrete of course.

3. I would appreciate any feed back that anyone has in general in dealing with this subject.

Thanks.

 

[whymrg]

We are working on the project with concrete floor and V=1000 microinches per second. In additon we have 44.5 feet span for girders and up to 35 feet span for beams.

I modeled floor in RISA-3D with T-sections for continuous beams and girders (cracked sections). From this model I got deflections at various points of the floor and used equations 6.3, 6.4 and 6.5 to determine vibration velocity.

I know consulting company that does FEA analysis for vibration but thay charge for their work.

The only publication that I could find is Publication SP-60 &quot;Vibration criteria for long-span concrete floors&quot; by D.E.Allen, J.H.Rainer and G.Pernica, published by ACI in 1979.

Hope this helps.

 

[lippie]

But when you calculate the deflections, you are using the transformed mom of inertia (equivalent steel mom of inertia) taking into consideration the composite action (with ribbing). This is then used in the deflection calculation (for beam and girder). So the concrete deck is being considered (the effective widths as well).

 

[haynewp]

The procedure is modeling the floor as an equivalent spring mass system as indicated on p.47. I think you are confusing local effects with how the SYSTEM will react as a whole in the form of vibration.