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RE: WOOD - Engineered Lumber vs. Sawn Lumber

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I have read through a few comments and want to add a few of my 
own.
If economically possible I would use only manufactured wood 
products. I find Parallams to be exceptional to GLB's. If you 
are not aware, you can order any Parallam with a Camber by 
specifying a Commercial grade Parallam and the appropriate 1.5DL 
camber.
I just finished a small Baptist Church design which required an 
auditorium with walls exceeding 16 feet in height (2x6 @ 16" 
o/c) with a TJL sloped top chord roof spanning 50 feet. To 
accommodate the tall wall and insure that it is straight, I 
specified the new Timber Strand Studs. This added about 10% to 
the material cost, but reduced the labor and scrap rate for 
dealing with crowned studs.

I can appreciate John Rose's comments about mixed sawn / 
manufactured lumber products however, I think my original 
concerns where the mix of parallam headers in conventional 2x 
stud walls. The height differences compared to sawn lumber are 
not that critical and easier to conform than trying to get a 
Glu=Lam into the same width wall.

My concern for LVL's like Micro-Lams has more to do with the 
misuse of them for top flange nailed connections. Micor-Lams are 
great for face nailing but can delaminate if top nailed. I also 
don't like the idea of splicing plies together in the field. It 
seems so much easier to order a full width member in Parallams 
which is generally carried in stock by most yards.

Finally, there is the environmental concerns that make 
manufactured lumber much more desirable. Mfg. wood products are 
harvested from young trees grown specifically for this purpose. 
No trees are removed from forested lands (according to older 
manufacture lectures) to produce TJ products. This means that 
mfg. products are self perpetuating without endangering existing 
mature trees.

If you haven't notice from the 1994 code, it appears as though 
the quality of wood that we are seeing in conventional lumber is 
not as desirable as it used to be. The grading rules have 
relaxed and with that the stresses have reduced. I've run into 
at least one problem with calculated beams deflecting greater 
than calced. Crowns can appear in the field due to changes in 
humidity and the concentration of cross-grain that is appearing. 
I'm not well versed in this area, but have had to do a lot of 
reading lately to understand how these problems occur when the 
numbers don't justify it. One informative book that I found is 
"Structural Design in Wood" by Stalnaker and Harris (Van 
Nostrand Reinhold Press). There is an excellent chapter on how 
defects occur in wood.
One interesting example is that You can not take a 20 foot long 
DF Select Structural, cut it into two beams and guarantee that 
you have two 10 foot long DF Select Structural beams. This was 
news to me. The reason is that the location of defects is a 
determining factor in the visual grading process. By cutting the 
beam in half, you my change the percentage of defects in each 
half as well as the location of the defect. This can 
dramatically change the grade of the lumber and it's applicable 
stress.

If I could, I would eliminate all the guesswork and design with 
only manufactured lumber.

My $0.50 worth.
Dennis Wish PE