Bending strength of lumber (2x4, 3x4) I keep finding conflicting info.
Bending strength of lumber (2x4, 3x4) I keep finding conflicting info.
(OP)

What is with this large variance in bending strength of Spruce-pine-fir. One table is from nelma.org Northeastern lumber manfacturering and the other is from the 2005 NDS.
Is there a standard/base bending strength/rule of thumb for bending strength of lumber? On alot of drawings I just see lumber called out as "2x4" or "3x4" with no specification to the species or grade of lumber, so there must be a base bending strength one can assume?






RE: Bending strength of lumber (2x4, 3x4) I keep finding conflicting info.
Stipulated strength reflects this. Also lumber sizes have changed... for example, a 2x4 used to be a 2"x4"rough cut, dressed it used to be 1-5/8"x3-5/8", it was actually only rough cut to a slightly larger dimension. Now a 2x4 is 1-1/2"x3-1/2" or the metric equivalent. A 2x8 is actually 1-1/2"x7-1/4".
Dik
RE: Bending strength of lumber (2x4, 3x4) I keep finding conflicting info.
RE: Bending strength of lumber (2x4, 3x4) I keep finding conflicting info.
You're looking at two different grading rules for the species - Spruce-Pine-Fir and Spruce-Pine-Fir-South. Find out which type of material is stocked in your area, then use the appropriate table of values.
Regards,
DB
RE: Bending strength of lumber (2x4, 3x4) I keep finding conflicting info.
Mike McCann, PE, SE (WA)