Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Dry Lumber

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Hi Nels,

Good Luck!  I can't answer your question, but am making comments on what I 
have seen and I am sure that you have seen similar.

I'm sure that you are aware that lumber is visually graded at the mill.  
Drying of lumber from 19 percent to 6 percent can cause it to degrade one or 
two grades.

According to the WWPA grading manual, you should be able to get lumber graded 
at MC12 and I think that I may have seen one or two pieces with a MC12 grade 
stamp.  You might be able to get carload lots from the mill and hope that 
they are not subject to rain while being transported.  Even then, reducing 
the moisture content to 6% can cause considerable shrinkage.  Since shrinkage 
is different in the longitudinal, tangential, and radial directions, getting 
pieces to shrink equally is quite a challenge.

I have a photograph of a wood beam (I believe it was a 6X12) bolted in a beam 
hanger that had 3/4" of space between the bottom of the beam and hanger 
seat.  The building was a panelized roof building constructed before they put 
slotted holes in the beam hangers.

If you are considering 4X and larger lumber, the surface can dry out very 
quickly, but the interior will take a long time.  Then you would have to get 
the lumber regraded if your stresses are critical to the grade.  You might be 
better off to consider manufactured lumber and if appearance is critical, 
sheath it with thin lumber manufactured by mother nature.

If you are using shear plates or split ring connectors, I would suggest not 
using more than 1/2 the allowable loads in NDS as I have seen split rings 
shear the lumber off the end of the piece even though the end, edge and 
spacing distance and loads were within those permitted by NDS.  Split rings 
will accommodate a little shrinkage, but shear plates won't, and splitting 
along the bolt line is common.

If you can design and detail to accommodate shrinkage, that would really be 
the route to go.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Nels Roselund wrote:

. > I'm designing repairs for very old buildings in a very dry location -- 
. > Death Valley.  I'm concerned about using lumber with moisture content 
. > that is significantly greater than the structural elements to which it 
. > will be connected.  I'm finding that 19% moisture content is the lowest 
. > that is available, even by special order -- even from the closest desert 
. > city, Las Vegas. The existing moisture content is probably in the range 
. > of 6% [+ or -]. I'd like to find lumber with moisture in the range of 11% 
. > or 12%, or less.

. > Do you know a source for lumber kiln-dried to lower than standard moisture
. > content?

. > Nels Roselund
. > Structural Engineer
. > South San Gabriel, CA
. > njineer(--nospam--at)att.net

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********