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30% reduction to Southern Pine Span Charts

Mule

Mule

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Oct 19, 2009
Messages
1,520
Location
Texas
Apparently all these years we thought that pine was the strongest of all wood. Well guess what? NOPE!

I am pretty good friends with one of the engineers that works for the Universal Forest Products. When I heard about this I emailed him and here is his email back to me.

It’s not a rumor. The final discussion will be taking place on Oct 20 with a publication of their decision on Oct 21. I expect SYP visual graded lumber values (not just MOE) to be reduced up to 30%. The million dollar question is, when will this be implemented. As I’m sure you are aware the span tables in the code could be invalidated once they publish the new standards. I personally expect the change to be implemented in 21-90 days after the announcement. The rumor on the streets is that it will be sooner rather then latter. No one that I have talked to expects the change to be implemented any latter then 90 days. We should know something in about 1 week.

About 1 year ago there were full scale truss test performed by our industry. During the test the lumber kept failing before it was suppose to. Our industry turned the test result over to the So Pine folks and suggested they look into it. They found our results to be a valid concern and took over there own investigation. The results/recommendations of their investigation are to be reported on Oct 21. The problems stem from new growth lumber and brash failures. The timber is being grown so fast that the old published values are not being met. MSR lumber should not be affected by this change from what I have been told so far.

After they publish their recommendation I plan to send the group an e-mail about what should be done in the short term and long term. Right now I don’t have any specific details and prefer not to cause a lot of concern when it is not needed.
 
From what I see in the field this is more of a grading issue than one that requires derating of the species. The NLGA rules are weak to the point of being effectively silent on the inclusion of compression and juvenile wood within a grade. If instead of derating the species the grade rules tightened up the exclusion requirements of these types of visibly apparent inferior wood this would solve the problem. Good SYP is as good as it ever was. Allowing one strength controlling defect to go unchecked into the grade is what is causing this proposed derating...grade out that defect.

I'm also not sure that this will not affect MSR lumber. Reaction wood in softwoods is unusually stiff for its' strength. Fb, bending strength, is derived from MOE, stiffness. Depending on how the sample set is picked when setting up an MSR run the bending strength values of the wood could be erratic IMO.

This is also not restricted to SYP, I gnawed on my supplier a week ago over a bundle of NS that he sent out. We walked out into the yard and I flipped through a bundle pointing out the large proportion of reaction wood in the pack. This further reinforces my feeling that this is a grading rather than a species issue.

Please do keep us in the loop as this develops.
 
Preview

Q – What effect will the new design values have on maximum spans?

A – Impacts on end uses will depend on the specific application but, in general, maximum spans for typical joist and rafter applications will be reduced.

Q – When will the new design values be in the building code?

A – The 2012 Edition of the National Design Specification® for Wood Construction is adopted by reference into the 2012 International Building Code®. If the new design values are approved at the October 20, 2011 ALSC Board of Review meeting, the American Wood Council (AWC) will include the new design values for visually graded Southern Pine dimension lumber in the printed version of the 2012 NDS® Design Values for Wood Construction Supplement. If the new design values are approved by ALSC at a later date, AWC will likely publish an addendum to the NDS Supplement at that time.



http://www.southernpine.com/using-southern-pine_design-values-qa.asp
 
And so all the jurisdictions in code 2006 and 2009 will be using inferior SYP until they adopt the 2012?
 
The wood isn't becoming inferior next week, we've already been using overrated wood... but yes you are correct.

They are faced with 2 choices as I see it. Tighten the grading rules, which would mean they are sitting on a whole lot of wood that doesn't make #2 or better at current design values. Or, allow this wood into the grade, diluting the strength. In so doing they preserve the ability to market this as structural lumber, and if you have to buy deeper sections for a given span, well that's a money making proposition too. Fox's rules.
 
In that the 2012 IBC and IRC for conventional light frame construction give the span tables by species, I fear that we will continue to use the old values until the 2015 code is adopted in 2016 and last use of previous code will be sometime in 2017, unless the state in the adoption process does a change at the request of the Homebuilders to keep the old tables that have "worked fine for years".
 
If the 2012 version of the NDS is modified after it was adopted into the IBC I would expect that to cause problems with IBC policies. I can imagine a number of other standards bodies playing similar games with the adoption process thus opening a can of worms. This might require special action by the ICC board or you might find the new values in the 2015 IBC.
 
That is a good question how did the 2012 AF&PA standards get referenced in the now published 2012 IBC and IRC when they are not yet available and likely will changed for commonly used southern pine? This will likely set up a conflict between the referenced standards and the span tables in the code derived from the standard.

I thought the standard had to be available by the final action hearings in order to be eligible for updating.

From chapter 35 of 2012 IBC--locations deleted

WFCM—2012 Wood Frame Construction Manual for One- and Two-family Dwellings

NDS—2012 National Design Specification (NDS) for Wood Construction with 2012 Supplement

AF&PA—2012 ANSI/AF&PA Span Tables for Joists and Rafters
 
I remember having to calculate the spans and providing the area builders with the span charts.

Modulus of elasticity formula, which I have forgotten.

pc1
 
Having span tables in the IRC was a stupid idea.
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Why?

Does it matter if they are in the legacy codes or the I-Codes or referenced. A reference to another publication would not always be the latest publication

2009 references

AF&PA-93

Span Tables for Joists and Rafters
 
Builder Bob said:
Wonder if this has anything to do with HUGO of 1989.......... severe weather has been whipping the poor ole' pine trees around making the wood twisted, weaker, etc.
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I don't know, BB. I hear the argument, even tho it might be very tongue in cheek, but as a resident of piney woods and a long time fan of SYP I have seen a steady decline of quality as far as growth ring spacing goes. Much of the pine lumber on the market today is so sapwoody that it has much less weight per unit of volume.
 
This is major news and I am surprised that there is not more discussion or public news about this. I wonder how the ICC will react or respond to this?

I agree with Brudgers that maybe tables in the IRC are not the way to go but reference to the most recent published data.
 
jar546 said:
This is major news and I am surprised that there is not more discussion or public news about this. I wonder how the ICC will react or respond to this? I agree with Brudgers that maybe tables in the IRC are not the way to go but reference to the most recent published data.
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I'm wondering more about how homeowner's insurance companies will react...seeing that I just got a non-renewal letter.
 
brudgers said:
I'm wondering more about how homeowner's insurance companies will react...seeing that I just got a non-renewal letter.
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Based on my experience with all kinds of insurance, any and all data newly published provide a rationale for raising premiums, in the boilerplate language of them all, "to better reflect the cost of providing the best level of coverage".
 
The current problem really predates hurricane Hugo and is a result of our silvicultural practices. If you want to read more on the wood tech side of this go to the FPL website and search for juvenile wood in the keyword search. These are a couple of good ones I remembered from there. The first one is a quick 1 page overview;http://www.fpl.fs.fed.us/documnts/techline/properties-of-juvenile-wood.pdfthis one is a good bit longer but goes into more depth;http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr129.pdfThis describes the annual and in grade SPIB monitoring process;http://www.fpl.fs.fed.us/documnts/fplrp/fplrp576.pdfThis is from one of the FPL's basic wood anatomy publications"Juvenile wood in softwoods is in part characterized by the production of axial tracheids that have a higher microfibril angle in the S2 wall layer (Larson et al. 2001). A higher microfibril angle in the S2 is correlated with drastic longitudinal shrinkage of the cells when the wood is dried for human use, resulting in a piece of wood that has a tendency to warp, cup, and check. The morphology of the cells themselves is often altered so that the cells, instead of being long and straight, are shorter and angled, twisted, or bent. The precise functions of juvenile wood in the living tree are not fully understood, but it must confer certain little-understood advantages.Reaction wood is similar to juvenile wood in several respects, but is formed by the tree for different reasons. Almost any tree of any age will form reaction wood when the woody organ(whether a twig, a branch, or the trunk) is deflected from the vertical by more than one or two degrees. This means that all nonvertical branches form considerable quantities of reaction wood. The type of reaction wood formed by a tree differs in softwoods and hardwoods. In softwoods, the reaction wood is formed on the underside of the leaning organ, and is called compression wood (Figure 2.18A) (Timmel 1986). In hardwoods, the reaction wood forms on the top side of the leaning organ, and is called tension wood (Figure 2.18B) (Desch and Dinwoodie 1996, Bowyer et al. 2003). As just mentioned, the various features of juvenile wood and reaction wood are similar. In compression wood, the tracheids are shorter, misshapen cells with a large S2 microfibril angle, a high degree of longitudinal shrinkage, and high lignin content (Timmel 1986). They also take on a distinctly rounded outline (Figure 2.18C). In tension wood, the fibers fail to form a proper secondary wall and instead form a highly cellulosic wall layer called the G layer, or gelatinous layer (Figure 2.18D)""The various features of juvenile wood and reaction wood are similar. In compression wood, the tracheids are shorter, misshapen cells with a large S2 microfibril angle, a high degree of longitudinal shrinkage, and high lignin content (Timmel 1986). They also take on a distinctly rounded outline"The S2 layer, or middle lamellae, is where all this is going on, it is the thickest and most important layer of the cell wall as far as mechanical properties are concerned. In good wood the microfibril angle in S2 is approaching the axis of the tree. In reaction wood it is much more horizontal, instead of a long break the cell snaps short and brash. I've attached a pic to show the structure of a cell.View attachment 1091That gelatenous layer he talks about in hardwood tension wood, the rubbery G layer, Native americans sought out leaner trees to make bows out of. The G layer is a rubber band.

View attachment 486

View attachment 486

/monthly_2011_10/572953c1630e7_cellstructure.JPG.bce054d56e24a80e234beeece5530217.JPG
 
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we no longer have any old growth timber,this is due to that. what happens is these little "p#cker poles" get sent to the mills, before the trees are mature. the growth rings are too darn far apart, they grow to quick, in plantations, not in a mixed forest with canopy that used to control (to some degree) the way the wood grew. its all to young, when wood started to get harvested faster than it regrew, the idea then was "give it more light and it'll grow faster", well yeah, but with more space around the trees, you get more sunlight, which produces accellerated growth, which gives you more space between the (growth rings) which directly affects the grain, which directly affects the strength of the wood.
 
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