Best way to stiffen I-joists 2

[pauljohn]

I am looking for the best way to stiffen I-joists to stop floor vibration. I have to use the minimum depth allowable by code for height reasons but realize the floor might feel too 'soft'.

Does anyone have any experience with this problem?

 

[boo1]

This is a common issue for residential I-joists. Please provide additional information, is the floor finished, is the underside accessable?

generic answers:
reseach manufactures web site for recommendations
Consider attaching with adding mid-span blocking
Screw (and glue) floor sheathing to I-joists
Enshure end of joists are secured from rotation
add additional joists
Sissor wood joist on I beams
use 3/4" 7 ply T&G A/C plywood

 

[pauljohn]

Thank you for your reply and sorry I should of been a lot more specific.

Floor has not been built yet and is still in design stage. It will be a multiple span length of 32' with the longest clear span of 20' below and 18' above. I would like to use the strongest 9.5" joist (BCI 6500 maybe ?).

But this span is far longer than product lit. recommends even though it is within code. We were dissapointed with the feel of a floor we just built that was within manufactures recommendation. (load deflection limited to L/480)

I will certainly glue and screw using 3/4" T&G. and will block at halfway or 1/3 - 2/3 mark. Other suggestion were box in joist with plywood one or both sides and use thicker T&G.

Obviously this will be a lot of extra work/cost which I do not want to do without knowing final result.

Do you think I am too far away from a stiff floor, to begin with, for some or all of these techniques to work?

Thanks for any help.

 

[boo1]

What company is BCI? Do you have there wed site? How are you determining that the design meets code? The span is outside normal diminsional lumber ratings and required engineering. Plywood both sides creates a stiffer box beam. The data (GP and TJI) I have indicates the joists do not work.

Consider using steel joists or beams.

 

[pauljohn]

BCI 6500 is made by Boise.
It's max. span allowed by code is 20'8" @12" O.C.

 

[pauljohn]

meant also to say I got the max. span data from Boise literature. Can't seem to access this particular info from GP (broken web link?) and I am not familiar with TJI.

 

[bylar]

Why would need to stiffen the joists. Use the correct joist for the span. It will be cheaper than trying to beef up the wrong joist. If you want to get rid of the bounce set your deflection to 1/720 or more. It looks like to me you ned the 11-7/8" joist min. I have had a great deal of troulbe with joist that are continous over 2 span. It seem that the load in one span is causing to much upward deflection in the other span. Once i started designing for single spans, that stopped. I still order the total length and after they are set in place we saw cut the top flange. This is easier to erect and has stopped the bounce.

 

[pauljohn]

bylar
You are correct about the right joist height, but I am trying to keep the height to a minimum to match the existing structure. If I use 11-7/8 I will lose height in first floor(already low ceilings) or have to make step up to 2nd from existing( my plan B). I am interested in your method to stop bounce in multiple spans is this widely used?

boo1
you say the other companies joists won't reach- do you think Boise Cascade are not being conservative enough with their data?

 

[boo1]

Review of Boise product line found Bylar's recommendation is correct for 11-7/8. The 9.5" wood I-beam joist does not work for the span. Consider gluelam beams

 

[boo1]

Consider
1-3/4 inches (45 mm) Flange: Cold formed Galvanized Steel
C-Joist, Floor System:
Size: 9-1/4 inches (235 mm) deep, 6-1/4 by 9 inches (159 by
229 mm) holes.
Minimum Delivered Thickness: 12 gage, 0.0966 inch (2.45 mm).

 

[UcfSE]

The glulam or LVL is a good option when you need a minimum framing depth. I agree with the advice to use the right joist instead of trying to stiffen the wrong one. If the joist depth you need doesn't work, then you need a different material. Closely spaced paralams or LVL's may work. If not you may have to consider steel framing. Either way, you don't want to start a job with a retrofit.

 

[pauljohn]

thanks for the replies and info. everyone. I am currently reviewing plans with local lumber yard for options and sizes.

Paul