I think it's in this standard, ASTM D245
http://webstore.ansi.org/ansidocstore/product.asp?sku=ASTM+D245-06.................
This is an example I have, not sure how much I can help you with it.
Fb=(5% exclusion limit)/(1.6 load duration factor*1.3 safety factor on 5% limit) = 5%-tile/2.1
5% exclusion limit =avg-(1.645*std deviation)
Suppose a number of 2x4's were tested in bending;
Avg=9138 psi
Std Dev=3205 psi
5%= 9138-(1.645*3205)= 3,866 psi
Fb= 5%/2.1= 1841 psi
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The "allfromr" link on this page might be of some help
http://www1.fpl.fs.fed.us/vicki/borinteractive.htmlMy copies of the wood handbook have psi's in table 4.2 preceeeding the metric tables. E is pretty close to those #'s. The new Emin in the 05 NDS is developed using similar methods to the above Fb example, I think.
Whoops I see you found it.
