Short split wood truss bot chord - reinforce?

[jittles]

Hello everyone, would love second opinions on a wood truss repair.

I've got a series of wood roof trusses ~5 years old and they show signs of minor splitting at their bottom chord splice locations. See picture below, bit hard to see.

Uniform across almost all the new trusses. To me it appears to be shrinkage restraint from the splice plate, maybe the wood was not completely dry.

Initial ideas:
Sister new 2x6 ea side full length - this is the truss supplier's (dumb and strong) suggested repair with no reasoning provided. Very difficult to install with plenty of stuff in the way plus floor space below occupied, excessive IMO.

Light gage steel plates w/ screws above/below the split to tie the chords together across the split, extend a bit beyond the current split. As long as the wood has now reached equilibrium and finished its shrinkage, this shouldn't exacerbate the split by adding more restraint across the member.

Clamp and run small diameter screws vertically through the split. This one feels most robust and direct to the issue currently.

Maybe there's a slick wood epoxy that might work to fill the splits and restore the section. This is probably the dream solution here but I'm unaware of anything applicable.

And the corollary to this is what to actually design the repair for. It is a tension member, with some potential for a ceiling to be applied to the bottom chord at some point.
Restore the shear capacity completely?
Restore cross-grain tension for a potential load applied to the bottom chord?


Any thoughts or opinions would be appreciated!

 

[kipfoot]

If you believe that the metal plate is sufficient, the bottom chord is sized adequately, and the cracks are related to shrinkage, then what do you hope to improve with these fixes? I don't think they help increase the tension capacity of the bottom chord, which is what this connection is all about.

Now, maybe the cracking reduces the capacity of the connection because there would be teeth that don't have the same 'grab' that they would with an intact piece of wood. That would lead me toward reinforcing the bottom chord with sisters fastened with screws into the bottom chord on each side of the joint.

 

[jittles]

kipfoot, you've hit on one of my issues. I don't believe the tension capacity really is compromised here.

But the issue has been raised and the truss supplier has recommended a fix, and that fix is realistically unreasonable to construct.

So now I'm trying to come up with some compromise where we can improve this without making it worse in other ways...


Hence, possibly considering a bottom chord load applied below the split. I can reinforce across the split so a hanging load engages the whole member depth. That is an improvement, albeit not to the primary function of the truss or bottom chord member.


Or, there is the option to recommend doing nothing at all. Owner, tenant, contractor all pushing to "do something" of course, but here I am at the forefront

 

[BAretired]

Looks like the truss plates prevented the wood from shrinking, causing cross-grain tension. I would be inclined to leave it alone for now, but if a ceiling is hung from the bottom chord, it should probably be wrapped all around to prevent separation...maybe a little duct tape would do the trick.

 

[dik]

That the condition is common, it's likely that the truss chord was quite green when the trusses were fabricated. The splitting doesn't likely compromise the truss strength since the splitting is parallel to the tensile stresses. For loading, only the shear capacity is likely affected, flexural capacity should be much the same.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[KootK]

I'd start with a chat with the owner about how they might intent to use the bottom chord in the future. Do they want to put ceiling drywall on it eventually? Would they like the ability to do some light storage in the attic, maybe 20 PSF or so? Then let that govern the design of the repair.

I agree with the others that the raw, tension capacity of the bottom chord has not been compromised meaningfully. What has been compromised is the strong axis flexural capacity of the bottom chords, particularly if loaded below their shear center. So it's down to the future use of those members being potentially subject to combined tension and bending loads. Hence the questions to the owner.

I'd do one of this:

1) Scab per the truss supplier but only do it between the panel points adjacent to the split. Maybe a couple of feet past that. There's no need to go the entire length of the trusses.

2) Add in some new webbing to create panel points near the splits.

 

[jittles]

I went and looked at some more trusses in other locations that were exposed, and sure enough this is a pretty common condition.

The black paint that was applied to the freshly installed trusses just makes those little splits pop out visually.

 

[RontheRedneck]

What the truss supplier proposed seems perfectly reasonable to me.

 

[BAretired]

What the truss supplier proposed seems perfectly reasonable to me.

How would a new 2x6 be attached to the existing chord to correct the problem?

 

[RontheRedneck]

On one side or both.

Although I don't see any reason to go the full length.

 

[BAretired]

But any additional nailing is going to split the existing chord above and below the current split, making the condition even worse than it is now.

 

[BAretired]

Whether a 2x6 is added on one side or both, it is still not clear how it can be nailed to the existing bottom chord without causing further splitting of that member.

The truss should be left as is (without doing anything). Dissuade the owner from adding a ceiling, for two reasons, 1. a ceiling will prevent him from seeing a problem developing and 2. he would be adding weight to the underside of the bottom chord.