laminated veneer lumber (lvl)

[massmanute]

The document "PROPERTIES OF LUMBER PRODUCTS" by Hernandez and Green, found at https://pdfs.semanticscholar.org/e90...952.1559122033 gives some engineering data that seems relevant. They list design values for various wood species of various grades. On page 6-122, for the highest grade of Douglas-fir/larch (select structural grade) they list a bending strength (fb) of 1500 psi. Note, this is basically an allowable design value which is quite a bit less than the values for average bending strength that you might see listed in some places. For the highest grade of spruce/pine/fir they list 1250 psi.

On p. 6-127 also give an example of bending strength for an LVL product of 2800 psi. This is fairly typical of values you will find in manufactures literature, but it is by no means the highest value one can find. For example, the Murphy LVL technical design guide lists a bending strength (fb) of 3100 psi for their LVL products, which is more than twice as high as the best grade of doug fir/larch. On page 6-125 they also make the comment "Generally the engineering design properties compare favorably with or exceed those of high-quality solid dimension lumber."

In terms of what would happen to the structural parameters if LVL is cut down, it is good to keep in mind how LVL is manufacture. It is manufactured in wide billets, which are then cut to less-wide sizes to give the standard widths sold in commerce. Manufacturers provide formulas for converting their standard values for bending strength, which are generally based on a 12" wide format, to other widths. For example, Murphy uses a multiplier based on the expression (12/d)^0.18. Thus, a their 5.5" wide board would be rated at 3567 psi whereas a 12" wide board would be rated at 3100 psi.

Manufacturers don't tell you how to rate an LVL board that you cut yourself. Some in fact tell you not to cut. That's probably lawyer talk to limit their liability. However, keeping in mind how LVL is manufactured, in which less-wide boards are cut from wider billets, which is similar to what one would do at home to make a less-wide board from a wider one, it seems reasonable to apply the same formulas they use to calculate fb for their standard sizes, e.g. (12/d)^0.18. Even if this is a not quite perfect predictor, it seems to me that the allowable bending strength of LVL is so far above that of natural spruce or Doug fir that it would provide an inherently large effective safety factor that would easily take up any slack in the analysis. And of course, one could also do one's own testing for structural members that are not too thick, such as material for stringers, just to be sure.

[Bill Berson]

32 pounds per cubic foot is same as Doug fir (from memory). So the glue weight is minimal. Sounds good to me.
Could boil a sample a few hours to test.