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Re: Steel Framing - Aerobic vibration criterion

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Gerard made an excellent point.  Any attempts to resolve the problem by the head-on increase of the beam/girder rigidity lead to the cost-prohibitive solutions. 
 
At the same time, the required natural frequency of the floor does not necessarily have to be taken from Table 5.3, it may be reasonably calculated from Formula 5.1.
 
Let's use Design Guide 11, Example 5.4 as an illustration.  Assume wp=4.2 PSF, wt=wc+ws+wp=1.1wc+4.2 PSF; f=2.75HZ, alpha1=1.5.  Based on this, to make the floor acceptable (say, fn_rq<=5.4, the concrete slab should weigh about 80 PSF (vs. 65 PSF), or be about 7 inches thick for NWC and 9" thick for LWC.   
 
This is totally doable - build a floor that is too massive to vibrate.  Make it 12 inches thick in the exercise hall, you are not in the seismic area, right? 
 
This approach is similar to that used for pedestrian bridges.  Such floor will not require any monstrous beams and girders, and may be inert enough not to vibrating.   The use of steel will be more effective, too. 
 
Another avenue to explore is the floating floor mentioned in the Design Guide.
 
Just a thought, and I would still try to contact Dr. Murray.
 
V. Steve Gordin, SE
Irvine CA
 
-- Original Message -----
Sent: Thursday, July 23, 2009 16:26
Subject: Re: Steel Framing - Aerobic vibration criterion

Also, thickening your slab or concrete fill over metal deck will get you more mass and perhaps more efficient use of materials rather than making the beams do all the work. Usually your beam is so big that it still works just fine for the added dead load since vibration governs.

As you are finding out, vibration has a huge effect on steel framing requirements (often doubling the weight per square foot) over areas designed for the same live load.

Make sure you have framing that is continuous over girders (meaning they line up on both sides of the girder, not necessarily moment continuity). Spans greater than 30 feet and you are looking at W30's - yes. Spans in the 24 foot range you should be able to get W24x94's in that range to work at a 7 or 8 foot spacing.

Floorvibe is a good program and AISC also has a similar program on their website you can download for free. Both are based on design guide 11. Floorvibe can work inside and outside of RAMsteel I believe.

I would not recommend using Etabs for vibration design as it appears to be very conservative.

-gm

On Thu, Jul 23, 2009 at 3:35 PM, Stuart, Matthew <mStuart(--nospam--at)cmxengineering.com> wrote:
Thanks Steve