WOOD DESIGN VALUES

[JKJohn]

I was called to evaluate a 1930 roof structure and the possibility of installing a roof top 1000 lbs A.C. unit.
I was not able to locate any grading or stamps on the 2x10 wood joists.
Any suggestion on how to find the design values for these joists?

 

[woodman88]

You can get a free download of the 1944 NDS from

http://www.awc.org/standards/nds.html.

Also some values from 1922.

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.

 

[JKJohn]

Yes. But how to tell what is the species and the grade?

 

[woodman88]

With lots of money and/or time. 1) Testing of the lumber. 2) Getting a grading expert to access the lumber, who's report you would be willing to except. 3) Calculating the required Fb would be and seeing which species and grades would work and using the minimum of what would be available in that area at that time. 4) Making an engineering guess based on what was normally used for lumber at that time and seeing if the calculations work.

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.

 

[woodman88]

If you decide of testing/regrading of the lumber be sure to have enough samples done. Back in the 1960/70's (not sure what it was like in the 1930's) it was fairly common for lumber grades (when a lumber company did not have enough of a lower grade or too little of a high grade) to combine grades in a #2 and better or #1 and better package for sale. I remember wood truss companies who brought the #2 and better to pull out all the #1 and SS for special use in the trusses. Not to be confused with the current #1 and better grade which is its own grade and not a package of grades. So if you are testing or regrading only a few pieces the answer you get may not reflect the actual grade used.

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.

 

[MiketheEngineer]

Do your analysis and figure out what you would like for an Fb... Then make your decision. It may be simpler than you thought - or maybe not!!