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Purlan Strength

Started by ronwood, November 07, 2005, 11:35:59 AM

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ronwood

I am currently building a lean to onto my existing building to put the sawmill. Yesterday I was sawing out some purlans from red oak that had been dead for sometime. The 2 x 4's (actual dim. 2" x 3 5/8 " ) has worm holes in the wood. I was wondering that effect that would have on the strength of the lumber. I am putting them on edge with trusses 90 in apart. Purlans are 24 in on center . Any thoughts would be appreciated.

Thanks
Ron
Sawing part time mostly urban logs -St. Louis/Warrenton, Mo.
LT40HG25 Woodmizer Sawmill
LX885 New Holland Skidsteer

beenthere

I would think it would depend on how much of the cross-section of the '2 x 4' the worm holes take out. If away from the edge then the holes shouldn't affect the 'tension' needed along that lower edge. However, holes are different than knots when away from the edge, as they don't have the supportive grain running around the knot, but are instead 'cutting' the grain off, thus eliminating some of its strength. But for the most part, if the worm holes are not along the edge of the piece, I think you will be okay.

Just a caution, avoid 'walking' on 2 x 4 purlins.  Too many have failed, causing too many people to be injured or killed, walking or trying to stand on purlins.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

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