R,C&S question

[Richard Brekne]

Just thought I'd throw this bit of info into the mix... something that 
strikes me as an argument in favor of very dried out panels that are 
kept in dry environments.

 From Hoadley

    "The strength of wood increases as the wood gets drier, although the
    rate of strength improvment is not directly related to the loss of
    bound water (as is the case with the shrinkage rate) property. For
    example, maximum crushing strength in compression parallel to the
    grain and fiber stress at proportional limit in compression
    perpendicular to the grain is approximatly tripled in drying from
    green to oven-dry*. Modulus of rupture in bending is more then
    doubled in the process, but the stiffness in increased by only about
    half. "

*oven dry taken as essentially near 0% MC.

The change in strengths are quite dramatic in the range of 25 % MC to 
oven dry. Static bending about 2 % for 1% change in MC,  Compression 
parallel to the grain about 6% per 1 % change in MC. I  surmise from the 
above quote this is comparable to compression perpendicular to the grain 
as well.

Added to the fact that strength in wood increases with lower 
temperatures it it would seem that keeping a board dry and cool would 
insure greatest strength levels over the long term. It also implies that 
similar levels of compression at different MC and temperature involve 
quite different abilities of a panel to sustain the degree of compression.

Cheers
RicB