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edselsouth1 05-01-2012 11:11 PM

Bridging or not?
 
2 Attachment(s)
I have a span of 12'5". The I-joists are 12" in height, and are on 16" centers. Do I need to use bridging between the i-joists, anywhere across the span? Bridging is being used at the perimeter wall. I'm using the metal bridging straps from HD/Lowes. Thanks, David.

AndyGump 05-01-2012 11:25 PM

I don't see how they would hurt anything other than your pocket book a bit.
But then I don't see how they might be useful either.

Andy.

Just Bill 05-02-2012 06:12 AM

Bridging in mid span always helps stiffen the floor with standard framing. Not that familiar with Ijoists, but can't see whay it would not help there also.

ddawg16 05-02-2012 08:34 AM

I'm using 2-12's in my construction....per the plans....if the span is more than 10', blocking must be used.

PIA....but after you put it in you understand why. Over large spans, even with the ends blocked, with enough load, the joists start to rotate at the bottom.....

Take a 1x6 pretty long....support both ends on edge....then push down in the middle....you get some deflection down...but what you really start to see is the middle starting to twist/rotate which drastically reduces the strength.

Even with my joists on 12" OC, I noticed a difference in stiffness once I put in the blocking.

(note to self, do the blocking before putting down floor sheathing next time).

Daniel Holzman 05-02-2012 08:58 AM

I joists are prone to local buckling, which is the torsion (twisting) described by ddawg. They do this more than solid lumber because of the thin web, which of course saves money on construction, but invites the potential for buckling under even moderate loading. Typically the floor above stablizes the I joist, assuming it is appropriately attached, but during construction there have been serious accidents associated with workers walking on unblocked I joists where they buckle and fail under load. Also, the floor above does not fully brace the lower flange, so blocking is often recommended or required by the I joist manufacturer, typically they have a complete set of recommended practices for installation, which of course should be followed.

framer52 05-02-2012 09:16 AM

Bridging is not required by any man. of IJOists

Daniel Holzman 05-02-2012 09:36 AM

For a full discussion about bridging (I joist lateral stability issues) see the "Manual For Engineered Wood Construction", Forest Products Laboratory, 1999. Section 4 states in part

"4.2 Lateral Stability
The design values contained in the evaluation reports
assume continuous lateral restraint of the joist’s compression
edge and lateral torsional restraint at the support locations.
Lateral restraint is generally provided by diaphragm
sheathing or bracing spaced at 16" on center or
less (based on 1˝" width joist flanges) nailed to the joist’s
compression flange.

Applications without continuous lateral bracing will
generally have reduced moment design capacities. The
reduced capacity results from the increased potential
for lateral buckling of the joist’s compression flange.
Consultation with individual producers is recommended
for all applications without continuous lateral bracing."

While this may not sound like English, it states pretty clearly that lateral restraint (bridging) is required. Exactly how these ideas are incorporated into different manufacturer recommendations for installation is up to the manufacturer, but lateral restraint is very important, I cannot believe there is a manufacturer who disagrees with this conclusion.

GBrackins 05-02-2012 08:06 PM

are you installing a subfloor (glued and screwed) on top of the i-joists? are you using strapping and gypsum board for the ceiling?

joecaption 05-02-2012 09:34 PM

We have used GP brand and I've never seen anyone use cross bracing on them. I checked there web site and there not even mentioned.
Not going to do any harm to have them.
http://www.gp.com/build/product.aspx?pid=1390

edselsouth1 05-02-2012 11:41 PM

Bridging or not?
 
Thanks to all who responded.
Looks like I will be installing some bridging about midway in the span, using the metal straps from HD/Lowes. I can understand where there might be some buckling/twisting at the lower ends of the i-joists.
GBrackins... There will be 3/4" t&g OSB (glued and screwed) installed on the i-joists, and finish floor on top of that.
Roxul, unfaced, for insulation on the underside, and 5/8" drywall for the ceiling of the garage (taped and finished of course). Don't know the type of final finish for the upstairs floor at this time.
I also have a 10' span that has 3/4" t&g OSB on it, and it seems rock solid, but I'll consider adding some bridging to that also. More might be better. Thanks,
David.

Gary in WA 05-03-2012 12:22 AM

Glue the groove of the T&G for optimum strength as per manufacturer of the decking.

Those are very similar to TJI's the ones we use here mostly. No mid-span or blocking is required (pp.3, top left in green color). Three rare occasions we added mid-span blocks per plan when a shear wall was above, out of 100+ houses. http://cmfac.groups.et.byu.net/tharm...ng%20guide.pdf

Do not use the MCA's for solid wood (with the pointed ends). You need the TB's; http://www.strongtie.com/products/co...nca-tb-ltb.asp

Gary

edselsouth1 05-03-2012 09:14 PM

Bridging or not?
 
GBR in WA.....
Yes, the i-joists appear to be very similar to the TBI 110 s. I have however, had to cut down two of the i-joists from 14" to 12". Clip the rail, route the groove for the web, fasten w/ Titebond III glue (waterproof), and clamp every 12". Let set overnight, and install.

I have glued the t&g 3/4 OSB, as well as glued and screwed to the i-joists w/ 2" construction screws on 12" centers. The metal bridging straps are TB s.

Thanks.
David.

Joe Carola 05-03-2012 09:58 PM

Quote:

Originally Posted by edselsouth1
GBR in WA.....
Yes, the i-joists appear to be very similar to the TBI 110 s. I have however, had to cut down two of the i-joists from 14" to 12". Clip the rail, route the groove for the web, fasten w/ Titebond III glue (waterproof), and clamp every 12". Let set overnight, and install.

I have glued the t&g 3/4 OSB, as well as glued and screwed to the i-joists w/ 2" construction screws on 12" centers. The metal bridging straps are TB s.

Thanks.
David.

Are you seriuos? If so, you've made a huge mistake...you can't do that. Who told you that you can do that?

edselsouth1 05-03-2012 10:14 PM

Bridging or not?
 
Joe Carola..... Sorry. To clarify: The two I-joists I cut down from 14" to 12" are only 2-1/2 feet in length, and are under an area that is to be used for a closet. Each end rests on a doubled 2x12. The closet area is in a corner above the end of the stairwell. The total area of the closet is 2' wide x 2-1/2' in depth. No one will be walking on this area! Thanks. David.

GBrackins 05-03-2012 10:22 PM

Quote:

Originally Posted by edselsouth1 (Post 913990)
I have however, had to cut down two of the i-joists from 14" to 12". Clip the rail, route the groove for the web, fasten w/ Titebond III glue (waterproof), and clamp every 12". Let set overnight, and install.

you are not suppose to cut the flange from off of the web and then re-glue the flange back on. But don't take my word for it.

I'd STRONGLY suggest you contact your lumber yard or where ever you purchased the I-joists from and ask them. You could call the manufacturer (online search will give you their contact information) directly and talk with them and what you'll need to do.

I would not proceed if this was my project without correcting this issue as it could lead to serious problems. There may be no walking on it now, but someone in the future could remodel the interior and think they had a solid floor.

Just my humble opinion. :wink:


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