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FRT wood trusses
3

FRT wood trusses

FRT wood trusses

(OP)
I have a building with light weight trusses (2" x 8" top and bottom chords with 2" x 4" diagonals) in which the diagonals have failed and pulled away from themselves at the top chords.  It looks like the wood may have been treated.  The project is circa 1980.  Need help with determining if the wood was treated, did the treatment reduce the strength and how can this be determined.

Thanks you

RE: FRT wood trusses

2
I wonder if it may have been constructed with the Canadian Lumber that was a problem back in the 80's.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: FRT wood trusses

I am going to guess that this is Fire Retardant Treated lumber - a common problem in the era.  And what you describe was rather typical.  Members not only pulled away from plates - but members actaully broke in some instances.

They only remedy I ever heard of was to completely replace the roof system - trusses and plywood.

Many lawsuits were filed over this problem  You can probably Google it and find them.

Sorry and good luck.

RE: FRT wood trusses

(OP)
What was the problem with Canadian wood?

RE: FRT wood trusses

It's been so long ago, I will have to look that up.  But there was a lot of flack over it with a lot of apartment projects here in Seattle.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: FRT wood trusses

Suspect grading stamps...

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: FRT wood trusses

If you FRTL as MiketheEngineer noted, check the truss plates.  They often corroded because of chemical leaching.  Further, look for a white residue  on the trusses...this is also indicative.

The wood, in early FRT processes, produced brittle wood.  Google
Hoover frt.

RE: FRT wood trusses

First, are they trusses made at the jobsite - basically 2x's gussetted together at every joint or are they metal plated wooden trusses?

If the lumber is treated in any way, the strength will be decreased unless the designer took that into consideration when they were designed. Probably best to get a PE to do the calculations ant tell you what kind of repairs are needed, but may be simpler and more cost effective to just rip it off an replace them.

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