reduced southern pine design values
reduced southern pine design values
(OP)
This may be old news to some, but new to me.
At a woodworks seminar today I learned that 'emergency' testing on southern pine wood has lead to the conclusion that there should be an immediate strength reduction for 2x4 SoPine due to more juvenile wood used in production.
Apparently the strength of a 2x4 SP will be reduced on 6/1/12. The official letter also 'strongly urges' to use caution when using other sizes as well as they may be reduced 25-30%
I imagine this being a real sh** sandwich for some design engineers, especially truss designers. I mean in a repetitive system it may not be so worry some, but for a 60' truss where one web member failing can cause a collapse, what are you to do uptil 6/1/12? It seems the grading or standard agency has put people in a tough place. They issue a statement saying values will be reduced for one size at a future date due to the fact they are currently understrength and future testing is needed for other sizes but they are also believed to be understrength.
I see this being tough for 'cut throat' truss engineers who will design with this knowledge in advance of 6/1/12, who won't?
http://w ww.souther npine.com/ using-sout hern-pine_ design-val ues-qa.asp
At a woodworks seminar today I learned that 'emergency' testing on southern pine wood has lead to the conclusion that there should be an immediate strength reduction for 2x4 SoPine due to more juvenile wood used in production.
Apparently the strength of a 2x4 SP will be reduced on 6/1/12. The official letter also 'strongly urges' to use caution when using other sizes as well as they may be reduced 25-30%
I imagine this being a real sh** sandwich for some design engineers, especially truss designers. I mean in a repetitive system it may not be so worry some, but for a 60' truss where one web member failing can cause a collapse, what are you to do uptil 6/1/12? It seems the grading or standard agency has put people in a tough place. They issue a statement saying values will be reduced for one size at a future date due to the fact they are currently understrength and future testing is needed for other sizes but they are also believed to be understrength.
I see this being tough for 'cut throat' truss engineers who will design with this knowledge in advance of 6/1/12, who won't?
http://w
EIT





RE: reduced southern pine design values
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: reduced southern pine design values
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: reduced southern pine design values
RE: reduced southern pine design values
The fact is that the values for SYP 2x4 Visually graded lumber are going to decrease. Now, does that mean that a switch just gets pulled in June and viola! we start having less strong wood. No, the values proposed are representative (due to testing) of the current (and past?) stock/supply of SYP. This is not a change where the lumber will be different starting in June. This is a change to reflect the reality of the actual test results. The wording of the release by the ALSC board of review is clearly meant to "inform" you and to use your best judgement with this information and in my opinion, they are attempting to limit their exposure to it. They are just following procedures... You, as the EOR or RDP need to be "responsible".
From the ALSC board of review minutes, Jan 5, 2012
"Although given the facts, circumstances and controlling authority of this particular matter, the Board did not approve design values for the other sizes and grades and has recommended a future effective date, it cautions all interested parties to take note of all available information in making design decisions in the interim. The values in the SPIB proposal represent approximately a 25-30% reduction. Many of the critics of the proposal acknowledged that some reductions were in order, albeit the magnitude of those reductions was disputed. All design professionals are advised in the strongest terms by the Board to evaluate this information in formulating their designs in the interim period."
(emphasis of original text (not mine), See attached file)
This is also not like there is now a new design method for wind design which is more accurate and several more chapters in ASCE 7. This is happening at the Strength side of the equation and it has been found to be the wrong values. Now we know about it but we are waiting until June to start "officially" using it. The question is, are you legally exposed to a failure?
Yes, Yes, there are a lot of conservative assumptions, statistical deviations, safety factors, redundant load sharing, blah blah blah. I have had my share of probability analysis and this issue is no different but I don't believe this has much of a place here. How many of you, when running the calculations of a joist, would look at the result "125% OVERSTRESS" and say, "yeah, I'm good with that" Knowing it applies to 90% or more of the members in the roof and move on.
To me this strikes at the heart of Life Safety. As for my part I know that I will be looking at truss drawings more carefully and I will be changing my truss specifications to use MSR only. As far as larger Lumber in SYP is concerned, I don't know. There are many decks with my name on them. The wording from the news releases implies changes may be forthcoming or are under review. I will have to wait and see. I want to believe the larger lumber sizes will be less affected due to what I believe the source of the problem: sourcing of smaller trees, utilizing juvenile and peeler core wood.
At the seminar someone mentioned that this entire issue came about because of an actual truss failure where they started to look at the strength values of the failed pieces. I have been unable to locate a source for this but I would be interested to see if someone else can shed light on the topic.
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MAP
RE: reduced southern pine design values
While the excuse of juvenile wood is being used, it hasn't been proven that is the cause.
RE: reduced southern pine design values
RE: reduced southern pine design values
I do most of my work in wood design and like to think that I stay up on things current. I knew something was going on since the end of last year but direct implication was not on the radar for me personally and wasn't really paying attention to it. The board or review meeting minutes of the ALSC are worded rather strongly and it appears that the magnitude of the value change took them by surprise as well as SPIB. Also interesting to note is the issue of timing and how to deal with that. Of ethical interest is the concern that a truss company may in fact try to push the market with getting it done before June 1 in order to save $$ for a project. As an EOR for a project would you let it go because the "official" value is still OK or would you impose the new values on the truss designer? Certain values are not "close enough" in my book and some are.
MiketheEngineer, can you honestly say that in the last 40 years you saw a strength reduction of 30%? Can you cite them? If this was steel or concrete would you be the same ho-hum? It appears that God didn't change anything but rather a lack of a feedback loop in the control system. The visual grade rules are still standing and it appears were all being done correctly. The problem stemmed from not doing much testing of the actual material and more to the point not having a trigger mechanism or feedback loop in place that flagged things being out of whack. That is why MSR lumber is not affected here. The other thing is that only the 2x4 were tested and are adjusted so the affected designs are mostly MPC trusses.
MAP
RE: reduced southern pine design values
EIT
RE: reduced southern pine design values
Is it new growth wood - maybe - but we have been "harvesting" trees much as we harvest corn for at least the last 50 years. Weyerhauser et al plant WAY many more tress every year than we cut down!!
And we MUST use good values to protect the safety and welfare of the public - just quit moving the target!!
RE: reduced southern pine design values
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: reduced southern pine design values
Personally, I'd be sweating more bullets if there were a report indicating that structural steel and high-strength bolts materials were compromised by 30%.
RE: reduced southern pine design values
RE: reduced southern pine design values
RE: reduced southern pine design values
EIT
www.HowToEngineer.com
RE: reduced southern pine design values
http://ww
RE: reduced southern pine design values