Sun, 24 Oct 2004 09:20:41 GMT Christopher Green wrote:
(snipped)


This one may be more easily accessible:

http://www.fpl.fs.fed.us/documnts/pdf2001/green01d.pdf

But I wonder if anyone has offered a math equation for stiffness of wood in relation
to strength of wood.

The PDF cited above includes an adequate review of the mathematics of
the many stiffness and strength properties that are used to describe
wood.

Some important points to get from reading that document:

Wood is orthotropic: its properties are unique and independent in each
of the Cartesian axes and in each shear plane. These properties are
very different from species to species, and not all properties vary in
the same direction.

There are standard measures of these properties, and there are
standard methods of measure. In the U.S., the procedures are given in
ASTM D143, which any library at an institution with a materials
science program should have.

Stiffness, or rigidity, denotes elastic resistance to deformation: it
applies at loads insufficient to cause permanent deformation or
fracture. Strength denotes resistance to loads that cause permanent
(plastic) deformation or failure.

The two are correlated, but the correlation is only moderate; there is
nothing like an equation relating stiffness and strength, nor could
there possibly be: the physical mechanisms at work in elastic
deformation and plastic deformation of wood are quite different.

For example, two important structural woods, Loblolly Pine and Red
Oak, differ to quite different degrees in stiffness and strength. They
are practically equal in stiffness: modulus of elasticity in bending
for Red Oak is 12.5 GPa; for Loblolly Pine, it is 12.3 GPa. But Red
Oak is noticeably stronger than Loblolly Pine: modulus of rupture in
bending is 99 MPa for Red Oak, but 88 MPa for Loblolly Pine. However,
Loblolly Pine is stronger in another important measu modulus of
rupture in compression: 49.2 MPa vs. 46.6 MPa. And if you are not yet
adequately convinced that there is no exact relation, note that Yellow
Poplar, a relatively weak wood in most other properties, is far
stronger than either in tension parallel to grain: 154.4 MPa vs. 101.4
MPa for Red Oak.

If not, then this science area has been neglected and very shabby.

No, it has been well understood for hundreds or thousands of years.
Mathematical development, of course, was possible only in the last few
centuries. But wood is such an important structural material that it
is not at all neglected. Any handbook of building materials and any
building code will have extensive data on the strength and permissible
loading of various types of wood.

That is a good website. It may have answered a question brewing in my mind as to whether
green treated lumber was stonger than untreated. Since wet lumber is weaker than dry, I
suspect green-treated or pressure treated is weaker than untreated, but do not hold me to
that speculation.

That website would have hit the jackpot for me if it had included the data on Hickory,
White Ash, White Oak, BlueSpruce and Honeylocust.

Because, if you remember, I hold a grudge between the acclaimed strength of Hickory
versus WhiteOak and the **obvious observation of the growth pattern of these trees**. The
growth of WhiteOak allows for the limbs to be parrallel to the ground whereas Hickory is
upward. That spooky oak look of whiteoak. So the wood would have to be **super strong**
to hold that weight.

So I need to see some data, Chris, that reconciles the obvious fact that WhiteOak is able
to throw limbs out parallel to the ground and hold them there whereas Hickory throws its
limbs upward.

That report has a reference to a science lab in Pennsylvania. Perhaps they ran hickory
and whiteoak and whiteash through their labs?

I need to see the data that will reconcile the observation of Whiteoak limbs parallel to
ground whereas hickory opts out for a weaker profile.

And while I am at it, I need to reconcile the fact that BlueSpruce foliage is so dense
yet able to withstand winds must translate into a superior strong wood compared to many
others. Again, another reconciliation of observation to numbers data.

So can you provide another website that has those numbers for Hickory, WhiteOak,
WhiteAsh, Locust and BlueSpruce.

Archimedes Plutonium
www.iw.net/~a_plutonium
whole entire Universe is just one big atom where dots
of the electron-dot-cloud are galaxies