New growth (faster-growing) dimensional lumber appears less strong. Do old standards need review? 2

[racookpe1978]

Trees (well, all plants actually) are growing 12% to 27% faster, taller, and thicker due to the greater CO2 levels in the atmosphere now (400+ ppm in today's world from the 2000's to 2017) than earlier (1940-50's-60's-70's) when CO2 was lower.

Fine, temperatures are neglibly higher (0.2 degrees, if even that much). But the faster growth means much wider growth rings, and the trees for structural lumber are now ready for harvest with many fewer growth rings across each dimensional lumber width, and each growth ring across a given 2x4 (or 2x10) is "fatter". I saw this when I tried matching grain patterns in my basement storage shelves: The 1970's 1x12's show a much tighter pattern, are noticeably harder to hand saw (stronger), harder to hand nail, and resist bending than the "new purchased (recent growth) 1x12's and 1x16's. (Yes, the new dimensional lumber is smaller/thinner than the older wood of the same nominal size - but that reduction alone doesn't seem to account for the greater bending under load. It just makes matching the shelf upper surfaces much more difficult.)

Granted, my simple shelves are not a calibrated "study" by any means, but the fact that the new shelves of the same "size" wood are bending further under the same load (books and boxes of records and papers) and need more reinforcement boards underneath, is troubling. Has the wood industry any review panels or professional groups re-evaluating the "basic" assumed strength for residential and commercial structural lumber?

 

[SwinnyGG]

If they aren't the same dimensions, they aren't going to be the same stiffness. The MOI funciton is a cubic function of dimensions- small changes have a large impact.

There's also a question of whether or not you are getting lumber that is the exact same species as what you already have on hand.

 

[SlideRuleEra]

Has the wood industry any review panels or professional groups re-evaluating the "basic" assumed strength for residential and commercial structural lumber?

In the US, the American Wood Council publishes the National Design Standard (NDS) which is the governing document for most wood design values. Good question for that organization.

A big exception is for southern pine lumber. The values are published in NDS, but are independently determined. Contact both Southern Pine Inspection Bureau and Southern Forest Products Association.

Basic research is performed by the USDA Forest Products Laboratory. This is where the science and experiments needed to establish updated criteria would likely be performed.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[SLTA]

There was a big shift in load values for southern pine back in 2013, I believe, for these exact reasons.

Please remember: we're not all guys!

 

[racookpe1978]

Yes, southern pine.

 

[berkshire]

One thing to bear in mind is that when a tree first grows the juvenile growth has much wider growth rings, as the tree matures the rings get closer and closer together. With most southern yellow pine The juvenile trees only have 4 or 5 growth rings per inch, Unless the standard has been changed. the timber was considered to be not much good unless it had at least 8 growth rings per inch. Of course the loggers cut by size so they may get a lot of fast growth that way.
B.E.

You are judged not by what you know, but by what you can do.

 

[Ron]

SLTA nailed it...check out the changes.

 

[berkshire]

That is quite a drop.
B.E.

You are judged not by what you know, but by what you can do.