sistering joists

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Steve-
I found an email I wrote back in 2005 to another engineer about a floor he was designing but the most important thing I found was this link to a Canadian report
http://www.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-173.html
The section about Vibrations from Walking is most applicable, particularly the last two paragraphs.
If you really want to reduce that vibration "go big" on the sister joists...... like ~ 2x12 engineered timber. But you'll lose ~5" of room height. :(
Robert Kazanjy 4/5/05 to seaint Dave-
Ralph's comments are right on target, I cannot emphasize too strongly that this could generate problem that dwarfs your design fee.
Talk to the customer (end user ideally).
This really could be a problem downstream depending on the room usage & their perception of the floor performance.
I highly suggest reading Canadian Building Digest CBD-173. Floor Vibration
http://www.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-173.html
I've done a fair amount of dynamic floor vibration testing & once people get sensitized to it, it can be a real problem making them happy.
I suggest forgetting about span/360 or span/whatever
deflection less than 1/16" under a 220 lb load is a good check. Also joists at 12 o/c are much better than 16" o/c. Blocking is generally not effective in achieving load sharing for vibration loading.
I'm not exactly clear on your floor system layout
You've also got to consider the dynamic response of the steel beams in conjunction with the timber; the floor system as a whole. If the customer is involved, has informed consent & is aware of possible consequences of the "cheaper" solutions you're much better off.
To prevent vibration you need stiffness or mass; your choice.
cheers Bob
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On 1/26/2012 12:07 AM, DD_BobK wrote:

Bob, thanks for all the info you've put up. I could afford to lose a little ceiling height, (it's 8'4" now). But it's not all that GREAT big of a deal. Also, my hvac and electrical is all finished, and i have a great big sun pipe coming down through there, so I can't sister EVERY joist. If it were before all this, I probably could have gone to a 10 or even 12" sister. It's just the two of us living here and the one room above is our bedroom and the other side of the upstairs (no partition) is her sewing room. There'll be no dances going on up there or kids running around.. LOL!
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Steve Barker
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On 1/26/2012 9:05 AM, Steve Barker wrote:

If you can loose a little ceiling height, how about a small beam perpendicular to the joists right down the middle, maybe a post in the middle could make it a very small beam? That would make things really solid and oh so much less work.
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On 1/26/2012 8:47 AM, Tony Miklos wrote:

I really did consider that option, but there's really not that much UNDER the floor (and no access) to hold the posts. PLUS, one of them would be dead center of a window.
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Steve Barker
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i would sister to a steel plate...........
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On 1/26/2012 10:01 AM, bob haller wrote:

that was my first plan over a year ago, but not worth the expense and hassle of procuring (and drilling) the the plate(s) for no more than i'm trying to gain. Thanks for the suggestion.
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When I paid a structural engineer to confirm what I already suspected was true, he advised, 16D CC nails 16" OC, 3 in a vertical row and 2 in the middle of the OC repeated on the other side in an alternating pattern. This was BNG (before nail guns) and I drove every one of those suckers by hand. In oak I would pre-drill with a 1/8" bit because of splitting hazard.
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Colbyt
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