Analyzing a Modified Queen Truss Repair (Calling all Kootks)

[Signious]

I just finished analyzing a 6 panel modified queen truss (38' span, end bearing) and just looking for advice on anything I may have missed.

1970s built truss on an anchorage acreage, early 2000s a reno was completed which moved the bearing point 9' (leaving a freaking 9 ft cantilever) in from the end with no changes to the truss structure, threw a couple of the middle web members into tension, and resulted in a sag on the top chord.

New home owner is taking the bearing back to the original design point, and I am double checking all is well. Visual inspection of lumber & truss plates show no damage, teeth still fully engaged (no tear out, no slip). Lumber is all 2x6 SPF in fairly good condition.

-Fully analyzed the truss for 25psf live & 15 psf dead, everything checks out (but vertical buckling on the top chord was close)
-Checked bearing & hold down req's
-Sizing new BM to support truss at end bearing point & dropping the mid-span bearing point they added in the previous reno.

Any concerns with this? I am mainly scared the wood top chords have permanent damage that is hidden from a visual inspection. Top chords are laterally braced the full length with continuous 1x6s. Would it be overkill to call for scabbing the top chord as a caution?

Thanks.

 

[msquared48]

Not an overkill at all to me. Use a good construction adhesive too as well as nails. Better safe than sorry. I was also concerned regarding the top chord deflection and any permanent deflection incurred.

Unlike strike breakers, scabs here are good, like on wounds.

Mike McCann, PE, SE (WA)

 

[KootK]

Ohhhh... I'm not sure that I've ever been summoned by fake name before.

I think that you're okay and have done your due diligence here. One of the nice things about wood is that failures usually happen by way of brittle, fracture mechanicy type events (depends on your definition of "nice"). If a thorough visual inspection yielded none of those, I'd feel pretty good about the wood. My main concern would have been the plates. And, if you're not seeing any withdrawal beyond about 1/8", I'd say that you're good there too.

I do think that top chord scabbing would be overkill.


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.

 

[Signious]

Thankfully they oversize the metal plates on this one (single cut members, but the smallest plate at a joint is a 6x6)

Thanks for input!