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Timber Unit Weight

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For the unit weight of timber, AASHTO requires 50 pcf. 

The AITC Glulam tables for Douglas Fir-Larch lists 35 pcf.  I believe the
difference in these two unit weights is due to expected in service moisture
content and the different specific gravities of various wood species.

Just for kicks, I checked into what the unit weight of Douglas Fir would be
at the fiber saturation point, about 30% moisture content.  Using the
equation at the bottom of Table M2, Appendix M, of the NDS I get a unit
weight at 30% mc of about 37 pcf.

Am I doing something wrong?



Unit Weight = 62.4*[G/(1+0.009*G*mc)]*(1+mc/100), G is .51, mc is 30%, so 

Unit Weight = 62.4*[0.51/(1+0.009*0.51*30)]*(1+30/100) = 36.4pcf

Doug Fredericks/CH2M HILL
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