huangyhg

wood i-joist vibrations
anyone have any experience with using wood i-joists. i am considering using them and wood like some input from anyone that has spec'd them. i am looking at span of around 20-25' with 5/8" flooring above. thanks.
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we used them, there cheap and light. no problems except there is little room for ducting. i used a higher deflection limit (l/480) with 3/4" apa t&g decking. we also used glue and screws for decking attachment.
you will get vibrations if you don't have a drywall ceiling attached to the bottom; a typical condition over a basement. two rows of solid bridging will help in that situation.
i use them all the time in both residential and commercial projects. like other structural systems mass dampens vibrations more than stiffness. i would definitely go with the 3/4" t&g sheathing. there are also some blocking details that mitigate vibrations. a local rep told me that to minimize uncomfortable sensations keep the span to depth ratio at 16 or below, but that sounded like using stiffness again. is this an open space (meaning no partitions being supported by the joists)? if so i would also consider using 1 1/8" sheathing. sheathing the bottom flange with gyp board also helps. heavier sheathing on top and gyp board on bottom also reduces noise transmission.
the manufacture should provide details to minimize vibration. see guides like:
also check out trus joists pro rating system. that gives you an idea on how "acceptable" the floor performance will be given your span and loading.
several manufactures have software to downlaod for free just check...
design for increased stiffness, say a deflection limit of l/480. this was the approach of the lgs industry.
first everyone is assuming this is for residential use, and you have normal loading.(no tile or concrete.) there are published span charts from the 3 major i joist suppliers,(trus-joist,lpcorp and boise.) if you have a crawl space with no bottom chord restraint i would take a foot off of those charts to reduce the vibration. with a 25' span it looks like you will have to 16" deep. unless it's use is for commercial. most of your lumberyards will know who the rep for each of these manufactures are and will give you their phone number
be careful with continous spans .
i used them on my own house with a deflection of 1/720
continous over 4 supports and i notice a lot of bounce in the joists.
spans 12'12' 12' bridging at center of each span
3/4" t & g decking nailed and glued no ceiling below.
but i have used them on severa projecst with siple spans and no problems.

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