Southern Pine design values and the IBC
Southern Pine design values and the IBC
(OP)
I know there have been several posts concerning the reduction in Southern Pine design values over the past year, but varying agencies and sources seem to be at odds on whether NDS Supplement 13 (with an effective date of June 1 2013) has already taken affect for all new IBC-based design or whether local jurisdictions must adopt the change.
The following from Southern Pine Inspection Bureau implies that enforcement varies by jurisdiction (see Q11).
http://www.southernpine.com/media/QA_NDVs_060113.p...
This "non-mandatory unless approved" sentiment is echoed in several other sources, but I was under the understanding that since ALSC (American Lumber Standards Committee)approved the change per IBC referenced ASLS PS 20, the values take affect June 1, 2013 and should be used for design without specific jurisdictional approval. (Sorry for all the acronyms)
Bottom line, if the local jurisdiction (under IBC 2006 or 2009) has not mandated the use of the new design values and has not approved any amendment to the prescriptive design sections of the IBC, do the updated design values have to be used?
The following from Southern Pine Inspection Bureau implies that enforcement varies by jurisdiction (see Q11).
http://www.southernpine.com/media/QA_NDVs_060113.p...
This "non-mandatory unless approved" sentiment is echoed in several other sources, but I was under the understanding that since ALSC (American Lumber Standards Committee)approved the change per IBC referenced ASLS PS 20, the values take affect June 1, 2013 and should be used for design without specific jurisdictional approval. (Sorry for all the acronyms)
Bottom line, if the local jurisdiction (under IBC 2006 or 2009) has not mandated the use of the new design values and has not approved any amendment to the prescriptive design sections of the IBC, do the updated design values have to be used?






RE: Southern Pine design values and the IBC
RE: Southern Pine design values and the IBC
Mostly I am curious if all engineers are adhering to these values or not.
RE: Southern Pine design values and the IBC
I just have my ways, it depends on whose ax to grind, who has to pay extra for what.
My battles with truss mfrs all boil down to how truss software works, and the local absurd practice of requiring me to show truss-to-truss hangers on my dwgs, despite what it says clearly ion the IRC, and the Bldg Dept knows that.
If I had to value-engineer a house for a tract homebuilder, using SP lumber, my advice would be opposite if doing a high-end custom home.
RE: Southern Pine design values and the IBC
A lion does not change it's spots.
Mike McCann
MMC Engineering
RE: Southern Pine design values and the IBC
RE: Southern Pine design values and the IBC
The shear in DF/DF glulams used to be 165psi. Now it is over 250 psi from what I recollect, maybe even higher.
Mike McCann
MMC Engineering
RE: Southern Pine design values and the IBC
Did you mean the shear stress increase in the 2001 NDS Supplement? There is an article on AWC's website that includes an explanation. See page 2 of http://www.awc.org/publications/Papers/NDS2001arti...
RE: Southern Pine design values and the IBC
The battle we fight is still the same, convincing others that wood members sitting in the lumberyard have changed properties overnight, but this time it is more difficult to blame it directly on the building code.
For those of you in the southeast who have been regularly specifying So.Pine as a comparable alternative to Douglas Fir, are you using reduced values? changing to MSR lumber or another species? or using the old values until you are directly forced to do otherwise?
By the way, here is the link to a SBC magazine article concerning this issue.
http://sbcmag.info/news/2013/sep/sbcas-public-lett...
RE: Southern Pine design values and the IBC
RE: Southern Pine design values and the IBC
Taking stud height as floor to ceiling height, or are you taking actual cut height of stud?
RE: Southern Pine design values and the IBC
RE: Southern Pine design values and the IBC
This should affect long spans more than short unless you are saying that these spans are deflection controlled anyway.
I would think exterior stud walls would see the greatest impact, especially tall gable end walls. Contractors already look at me funny when I make them use full height gable studs instead of splitting the wall at the plate. Now when I tell them they have to use an even tighter spacing than before they are really going to think I am overkilling it.
The other thing that makes this situation strange is that a jurisdiction that has not accepted the amendments to the IBC prescriptive design tables would still allow the old span tables to be used per the IBC but would "punish" engineered design assuming they must use the reduced design values.
RE: Southern Pine design values and the IBC
I have always taken for granted the gables get full height studs. Wouldn't there be a hinge otherwise?
RE: Southern Pine design values and the IBC
I think yards with wood in stock, and contractors and truss yards who could by outdated grade lumber cheaper protested the most. Everyone liked to point to the exact date that the new code went into effect, but the fact of the matter is mother nature's wood strength didn't change the day the code went into effect. The code simply codified more accurately the actual strength of the lumber. Remember when tension in lumber was the same as tension in the extreme finer in bending? And then all of a sudden, oops, better reduce that by 50%. The lumber didn't really change, but our understanding improved.
I think the new SYP values are the state of the art. I kinde prefer that the engineering profession lead this implementation and not leave it to the building officials. But, a contractor with a buck to make, can be a challenge.
RE: Southern Pine design values and the IBC
RE: Southern Pine design values and the IBC
RE: Southern Pine design values and the IBC
according to this, the factor of safety is a bit higher than 3.5-4.
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr190...
wood rupture properties are quite high. Variability and imperfect members cause the safety factor to be quite a bit higher as these are average rupture properties. I'm sure the factor of safety is 3.5-4 for the bottom 2-3% of wood in a normal distribution scale, but closer to 10 for the average piece of lumber.
RE: Southern Pine design values and the IBC
"I'm sure the factor of safety is 3.5-4 for the bottom 2-3% of wood in a normal distribution scale, but closer to 10 for the average piece of lumber. "
I am glad you pointed that out, because quite coincidently, I attended a wood design seminar last week, and they explained that the Code-writers did that for the EXACT reason. Whew.
RE: Southern Pine design values and the IBC
It's the internet so I'm having trouble detecting if your being a jerk or not. Seems that you are.
RE: Southern Pine design values and the IBC
The internet is not like conversing in person.
Sorry for any misunderstanding, English is my second language, altho I live in the USA>
RE: Southern Pine design values and the IBC
The internet is not like conversing in person.
Sorry for any misunderstanding, English is my second language, altho I live in the USA> "
I've seen your posts numerous times and you have perfect english so now I'm not sure if you're straight up trolling me. Whatever.
RE: Southern Pine design values and the IBC
RE: Southern Pine design values and the IBC
RE: Southern Pine design values and the IBC
But I am saying that I was totally not realizing I sounded so sarcastic - I can see that now re-reading my post,
No harm intended.
RE: Southern Pine design values and the IBC
RE: Southern Pine design values and the IBC
RE: Southern Pine design values and the IBC
Now i will state that when analyzing older SYP i would use the old NDS value (say 2003 construction) but new members for repairs will be for new reduced values.
And Thank you AELLC, I have ended up numerous online conversations coming off as a jerk when i did not intend. Now i do not feel alone anymore :)
RE: Southern Pine design values and the IBC
I started this online stuff way back on AOL in one of those chat rooms (actually the Architectural chat room)
Have a hundred war stories there - and we baited and tortured rude newbies mercilessly there.
RE: Southern Pine design values and the IBC
The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.
RE: Southern Pine design values and the IBC
"Why do the strength reductions only seem to affect short spans? The fb values saw a significant reduction (20-25%).
This should affect long spans more than short unless you are saying that these spans are deflection controlled anyway."
Yes, because, in my experience, serviceability seems to control most designs in wood construction.
SYP is rarely used for walls or roof framing (in our area anyhow). Usually only for floors and beams. That is because SPF is lighter and straighter.
RE: Southern Pine design values and the IBC
RE: Southern Pine design values and the IBC
RE: Southern Pine design values and the IBC
RE: Southern Pine design values and the IBC
RE: Southern Pine design values and the IBC
SPF for 2x4 and 2x6
SYP for 2x6 and up
RE: Southern Pine design values and the IBC
www.idecharlotte.com
RE: Southern Pine design values and the IBC
The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.