Longitudinal Shrinkage on Kiln Dried MSR

[Warrick]

Looking for some help - Need an authority or expert on Shrinkage, especially longitudinal shrinkage, on Kiln Dried SPF MSR.

Welcome any suggestions

[beenthere]

Welcome to the Forestry Forum. Can you expand a bit on your question. Wood doesn't, for all practical purposes, change in the longitudinal direction. However, in a piece of wood, all the wood from one end to the other isn't straight with the piece and 'longitudinal', so the grain around knots or the grain running diagonal to the long edge will exhibit some of the tangential or radial shrinkage rates. So, I'm assuming you are talking longitudinal to the board, and maybe not longitudinal shrinkage of the wood.  ??  Need more info. 
Are you in a lawsuit? 
I'm further assumming by MSR you are talking about Machine Stress Rated SPF lumber? 

[Warrick]

Hi and thanks for the reply.

Issue at hand is one with US Customs regarding pre-cut truss components - I would like to provide some information to them that for SPF Machine Stress Rated lumber which has been kiln dried, that it can be pre-cut to specific lengths and used in a truss application without the worry of shrinkage on the longitudinal aspect. 

Hope this provides more information

[Tom]

Check out this publication.

One Government organization should appreciate the other, don't ya think? 

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm

Look at chapter 3.  It describes shrinkage and even gives charts for radial and tangential shrinkage of many woods.

[Warrick]

Thanks Tom:

Actiually had a good look at that chapter last night and will see what I can do with some of the information.   Appears that the other government agency has an expert who claims that SPF KD stock cannot be pre-cut into truss components since it will shrink, especially on the longitudinal plane and therefore not conform to the truss sepcifications.  These components are also mainly used in Arizona, not a place where you would pick up alot of moisture.  Other than Chapter 3 - would you know of any position paper or "expert" in this area whom I could contact?

Thanks again

[Tom]

What I provided is the best that I know.  As far as Experts:  I have my own opinion of "expert" and we have some of the finest.  Whether their formal education would support the title in a court of law is beyond me.  This forum is moderated by Dennis Socling, a kiln expert and owner of PC Specialties,  and visited regularly by Sponsor Don Lewis, owner of Nyle Kilns.  I consider both of them to be experts in their fields.

http://www.nyle.com/

http://www.pcspecialties.com/

[Warrick]

Many thanks for the help and the recommendations

W.

[Larry]

Little off topic but can somebody explain "machine grade" to me?  I bought SYP trusses few years ago and the lumber was all stamped machine grade...no idea what it means.

[Warrick]

Never hear of Machine grade before - usually for trusses it is Machine Stress Rated meaning it was tested for strength and bending properties using a special machine - this machine will assign it a rating such as 1650f or 2100f which then allows it to be used according to the requirements of a truss.  Hope this helps

W

[Don P]

Dr Frank Woeste at UVA is as close to an expert in that field as you're going to find.
http://www.woodscience.vt.edu/contactlists/facultydetail.asp?facultyID=17

Larry, my understanding of the machine is that it has 3 rollers, 2 below 1 above. The upper roller applies pressure and gives feedback as the lumber passes through. The sensors give Modulus of Elasticity (deflection) and from sampling they have a correlation formula between MOE and Fb.
Look at visual graded design values and MSR numbers while visually appraising the 2 stacks of wood sometime  .
You'll also find MEL stamps, machine evaluated lumber. The numers usually go from M1 to about M23, then you have to look up the design values for your stamp.

[jimF]

The occasion when longitudinal shrinkage is a problem is when the material contains juvenile wood.  This is wood that growths differentlly than mature wood and is the first 7-12 growth rings in a tree.  There have been research/documentation of trusses changing shape to the extent that the ceilings were lifted up off the walls by about 1.5 inches creating a corresponding crack between the wall and ceiling.  Or if the trusses were nailed to the wall the wall being lifted off the floor.  If you need more information I can pull the articles out of my files for you.

[Don P]

Don't forget compression wood also, I've seen more in the last 2 weeks than I ever thought someone could accumulate if they were trying  .

 I can't believe I said Dr Woeste was at UVA... VA Tech