TJI Bridging or Blocking

[BSVBD]

Does anybody use blocking are bridging at mid-span (or other) for TJI roof or floor systems?

I've been told for many years that the typical TJI system does not require bridging or blocking because of their "structural integrity" or similar expression.

Unless you specify the 360 or 560 series TJI joists, and the span is not excessive (open to debate or discussion), the "slenderness ratio" for the 110, 210 or 230 series is not much better than any other slender element joist.

I have a project where I WILL be providing solid blocking where RTU's are bearing on LVL's that are amongst the TJI's, BUT... I would also like to specify bridging or blocking for the rest of the system, but, that tends to go against the current trend.

Comments? Thank you!

 

[jayrod12]

I specify that it is as per their documentation. If they require it, then it better be in. Although where I'm from it's a fully pre-engineered system.

If, you needed it for diaphragm action, then that's on you to specify. Otherwise it'd be up to them.

On the random topic of TJI diaphragms, see the attached.

 

[JoshPlumSE]

I was just reading some information on floor vibration of wood floor systems due to walking excitation. One of the remedial measures was to specify blocking between TJI joists The idea being that it spreads out the vibration across more members of the system. Activating more mass and damping and such.

 

[dhengr]

BSVBD:
Don’t the manuf’ers. actually make, or can’t you make up blocking from an extra TJ member or two? Then, you still need web to web blocking (2x3 or 2x4, short of the chord to chord vert. dimension) to fix the blocking pieces to the joist web. It seems to me I’ve seen that done. Why wouldn’t a piece of plywd. diaphragm material work just as well? Put the 2x3 web blocks on opposite sides, during your pre-fab., so you can just rotate the blocking in btwn. the TJ’s on installation. Probably, screws would work better than nails because these fasteners must work in tension to be affective. Think about penetration and pull-through on the OSB webs. The TJI people pitch the fact that their product doesn’t need the same amount of blocking/bridging as solid sawn, so that’s some labor savings for their system. Then, they’ll also blame some floor squeaking on any blocking, and you can fight about that. They don’t like you using X-bridging becuase there is no good way to fix it at its ends, and it ends up imparting a tension component (unzipping force) on the glue joint btwn. the web and the bot. chord member. That’s still a no-no. Why isn’t the LVL (or some such) a curb, for the RTU’s, above the roof? That would certainly help distribute the concentrated loads to adjacent joist. And, that’s basically what blocking or bridging is intended to do.

 

[Shotzie]

The Forte software has options in the floor performance tab to provide strapping, bridging or blocking, which will improve the "TJ-Pro Rating" which measures perceived floor performance. This could be useful if the client is worried about bounce in the floor. There's also this

http://www.woodbywy.com/trus-joist/taking-the-bounce-out-of-floors/

which talks about other ways to help improve the performance of the floors.

 

[KootK]

the "slenderness ratio" for the 110, 210 or 230 series is not much better than any other slender element joist.

I think that this is an important observation. As others have noted, there are a number of reasons for blocking and most of them are related to serviceability issues which could, potentially, be set aside if the product performs well. There is one use for blocking that is more critical however: in roofs with uplift, the blocking provides lateral torsional buckling resistance when the bottom flange goes into compression. The slenderness that you mentioned will kill 'ya there.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[CBSE]

JoshZum: yes, adding blocking improves the vibration of the floors. I have tested it with a contractor before...not scientific, but we did one side of the room with locking everyb4 feet and the other side without blocking. For lightly loaded systems (1-3 people) the load share was very noticeable. For a party type environment...well, the floor was still really bouncy...not that we had a party or anything

KootK...I have specified blocking in roof systems with i-joist before for that reason. But afterwards questioned my logic because gyp board was attached to the bottom side. I believe that provides enough connection to consider the bottom flange fully raced in an uplift condition. I you had a drop ceiling it certainly would be different.

 

[hokie66]

A recent discussion, with some links.

thread507-420136

 

[KootK]

I certainly agree that properly attached ceiling sheathing will brace the joist compression flanges under uplift moment reversal.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.