Floor beam deflection limit to avoid vibration

[nickky]

Hi,

We know that code gives a max deflection limit (for example L/240 for D+L) but I have had beams (specially longer spans)whaich had been designed based on L/240 but there was vibration there.

What would be your recomendation for limiting the deflection of floor beams (wood or steel) to avoid annoying vibration but in the same time to be reasonable as far as economy and cost.

Thank you!
Nick

 

[KBVT]

I've always used L/480 (LL) and L/360 (TL) where I thought vibration would be a concern in wood-framed structures. This is a rule of thumb I received back in my college days from Dr. Frank Woeste at Virginia Tech.

 

[paddingtongreen]

The L/240 is to avoid cracks in plaster etc. Natural frequency does not have a straight line relationship with deflection. The AISC used to have a pamphlet on this but they withdrew it.

Look here:

http://www.eng-tips.com/viewthread.cfm?qid=28892&page=1

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[steellion]

You should track down a copy of AISC Design Guide #11. It is worth the cost if you need to buy it. Limiting deflection and vibration in steel beams can be accomplished in the same way (increase the "I"), but it is a lot more involved than that, particularly if you're designing for rhythmic activity or sensitive equipment.