specific gravity of lumber
specific gravity of lumber
(OP)
ok, folks. Why is the specific gravity of dense select structural the same as the specific gravity of No. 3 and Stud? Pick up the same length of the same size of those and the DSS is CLEARLY much heavier, and therefore more dense. So why is this not reflected in the NDS?
Please remember: we're not all guys!






RE: specific gravity of lumber
Maine EIT, Civil/Structural.
RE: specific gravity of lumber
Please remember: we're not all guys!
RE: specific gravity of lumber
From the this link, http://www.astm.org/Standards/D1990.htm.
"1.3 Due to the number of specimens involved and the number of mechanical properties to be evaluated, a methodology for evaluating the data and assigning allowable properties to both tested and untested grade/size cells is necessary. Sampling and analysis of tested cells are covered in Practice D2915. The mechanical test methods are covered in Test Methods D198 and D4761. This practice covers the necessary procedures for assigning allowable stress and modulus of elasticity values to dimension lumber from In-Grade tests. The practice includes methods to permit assignment of allowable stress and modulus of elasticity values to untested sizes and grades, as well as some untested properties. The practice includes procedures for periodic monitoring of the species or species group to quantify potential changes in the product and verification of the assigned design values through, evaluation, and reassessment."
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: specific gravity of lumber
So does that mean that I should just relax about it? I am following the code, but the clear difference in weight between grades still has me perplexed.
Please remember: we're not all guys!
RE: specific gravity of lumber
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: specific gravity of lumber
The problem is that there is no ‘one’ perfect (exact) value for many of the properties on such a variable product. What Garth was testing for, he wanted the min. S.G. or density within the product group so his truss plate testing (or design values) would be conservative. He used the lesser value and thus most of the testing should have proved-out to be better than the min., on all the higher density pieces. In your case, you are concerned about DL, and the conservative approach is to use the higher S.G./density so as not to under estimate the dead load. Knowing what you know, nothing prevents you from adding a pound or two to your DL estimates before you start your design. I’ve never been a great believer in skinning the design loads to the bone before I start my design. Soon enough, you will wish you had a few extra pounds of design load to fall back on, when some guy/gal asks you to rationalize a bull they shot during construction.
RE: specific gravity of lumber
Kinda depends on what you are designing. A house is not so critical, but not so with a boat. Just a thought.
Mike McCann, PE, SE (WA)