Southern Pine strength/span reduction

[Don_P]

SYP has been undergoing testing over the past year and was failing below expected design values. The design values for several properties are about to be lowered by up to 30%. This will affect allowable spans/loads significantly.

More here;
http://www.southernpine.com/using-southern-pine_design-values-qa.asp

http://www.sbcindustry.com/docs/2011_10_12_Developments_regarding_Design_Values.pdf

[Ernest T. Bass]

Seems like the effects of our ever-decreasing quality of wood is always rearing its ugly head...

[rick91351]

Interesting to me they are not talking of changing grading rules to take into account for this.

Do you feel part of the reason for the strength / span reduction would be less mature trees going to mill and market?    

[Don_P]

Bingo Rick,
I've posted pics of compression wood and juvenile wood here in the past I think. Juvenile wood contains alot of compression wood as well, also known as reaction wood. That is the culprit IMO. The grading rules have a very weak sentence on grading compression wood and that sentence is entirely ignored on the grading chain, it has no teeth. Plantation pine is grown as fast as possible at the fastest possible rotation. Trees grown under those conditions contain far more reaction wood than a "normal" tree. The wood is weaker, breaks short, brash, and brittle. The microfibers that make up the cell walls are oriented at an angle to the axis of the tree rather than being aligned with the axis of the tree. The lignin content of the wood is higher. Think of the fibers as rebar and the lignin as concrete. The wood goes from an ideal mix of steel and concrete to basically unreinforced concrete.

Now, if you were a big industry holding alot of inferior wood, which would be preferrable... tightening the grading rules, which would effectively drop a whole lot of wood below #2 and make it unsaleable for structural use, or would you lower the design values which would mean people had to buy a deeper member to span a given distance.

The good wood out there is the same as it ever was. Industry and the regulatory agencies are bowing to the least common denominator.

IMO of course.

I chewed out my supplier a week or two ago over a batch of eurotrash he sent me that was full of compressionwood. I think this species might be just the tip.

[MountainDon]

Very, very interesting stuff.

Another reason I guess to not push limits to the maximum when consulting tables and charts.

So if SYP salls into this it makes one wonder about all the other lumber we buy. How much of the DF, H-F and S-P-F that we use (in the west in particular) may be subject to the same measurable degradation in quality/strength?