Full Height Blocking At Bearing Lines, Wood Construction

[bigmig]

What is everyone's take on providing full height wood blocking between floor joists
at the location where the joists span over a middle beam? Do it? Forget it?

Someone in passing said that BCI, the wood floor joist manufacturer in the US, was not recommending this......I've done it for years in
an effort to transfer lateral loads from diaphragms to center "strut" elements.

Thanks in advance.

 

[jayrod12]

In regards to the lateral loads. Most definitely it is required.

I'm a fan of provided them regardless. Especially if there is a bearing wall above as well. Perhaps teh I-Joist and Wood Truss guys disagree. But I haven't heard anything of the sort.

 

[phamENG]

Do it. More than likely, the beam stability factor was assumed to be 1.0 based on the assumption that the joists can't rack over the support. Review NDS 4.4.1.2 (e). This would apply to anything with an aspect ratio of a 2x10 or greater, but good practice to apply it across the board as bearing points are a concern for all others (though specifically at the ends for smaller aspects).

 

[XR250]

My experience with full-height blocking on i-joist floor systems is that it causes humps and tile cracking. The reason being is that typically long-spanned, continuous I-joists create enough crushing in themselves and the beam to sink down a bit. The blocking has no vertical load (except if under a bearing wall) so it ends up sitting proud of the adjacent joists.

 

[jayrod12]

XR that's interesting. I could see that beam a true issue. Do you feel that blocking between these deep joists that maybe isn't full height is still a good idea? I feel like if you've got 16" deep I-joists, you still want something to prevent roll-over? So maybe stick 14" high blocking between the joists (either cut to the profile of the I-joist or have web blocks installed to bring it flush with the flanges) which would allow the sub-floor to move down with the joists, but still provide the lateral roll-over stability joists of that depth scream for?

 

[XR250]

@jayrod12,

For the record - I despise I-joists and avoid spec'ing them unless i get a bunch of pushback from the Contractor.
I'm ambivalent on the blocking except under bearing walls. The floor diaphragm braces the top and the girder braces the bottom. I imagine, in theory, all of the joists would try to roll the same direction and cause the girder to translate while dumping a bunch of shear into the floor diaphragm. I believe the reality is that there will be some cancellation in the instability. If you go with the blocking, 14" may not be tall enough to catch the top flange of a 16" joist. Perhaps ask the framers to rip a 1/4" off the joist that is cut-up for blocking.

 

[msquared48]

I always specify full depth blocking between joists over beams. No exceptions.

Mike McCann, PE, SE (WA, HI)

 

[phamENG]

XR - can you elaborate on the crushing? Are you referring to actual crushing of the flange at bearing, or more of an elastic shortening phenomenon? If the former, there's definitely a problem - if the latter, web stiffeners can help. Some guys I've worked with in the past used to specify them for joists of a certain length and/or depth - probably for the reason you mention here.

 

[XR250]

XR - can you elaborate on the crushing? Are you referring to actual crushing of the flange at bearing, or more of an elastic shortening phenomenon?

My experience has been actual crushing of either the beam, the I-joist flange or both. Crawlspaces with high moisture levels seems to make it worse.

 

[phamENG]

Got it. Thanks for clarifying. I see you're in NC, so we're probably dealing with very similar climates - most of my wood design experience is just north of the border in VA. Due to the moisture levels, crawl spaces are all but gone in our area. Nearly every new house is a slab on grade (or slab on fill if they want that elevated look) and the TJI's are used on the elevated floors. I have seen plenty of crushing in crawl spaces, though, especially in flood damaged houses, though basic humidity does plenty of damage, too.

 

[XR250]

Crawlspaces are still a thing here (central NC) but many of the new ones are sealed. Tract builders here do love slab-on-grade however, with TJI's or trusses on the upper floor systems.