wood species question

I'm posting this for the normal people in this group who might thing that
this "Morgans" clown actually has some kind of valid point.

His remarks make quite clear that he doesn't know the first thing about
structures. Yet he comes out with guns blazing and hurling unprovoked
insults. What a clown.

For example, take his comment about modulus of rupture not being relevant to
stress in compression or tension.

This is complete gibberish that shows he doesn't understand even the basics.
Modulus of rupture is a measure of a material's strength in bending.

Bending loads on a piece of wood (or other material) typically produce
stress in both compression and tension at the same time.

Take a wood yardstick and hold it by the ends; now try to bend it into a U
shape. The wood fibers on the inside of the curve will be in compression,
while those on the outside will be in tension, simultaneously.

If you apply enough bending moment you can break the stick. But what if you
bend it as far as you can without breaking it and then let it go? Have you
done any damage?

It's quite possible tthat you have damaged the wood fibers that were in
compression (the top of the stick). Almost certainly you will not have
damaged the bottom of the stick, which was under tension.

The reason is that wood is about two to three times stronger in tension than
in compression. So while you didn't break the stick, you might have caused
compression failure on the side of the stick that was on the inside of the
curve. This damage would be most acute on the top surface of the stick and
would be progressivly less until the neutral axis (middle) of the stick.

If you made a saw cut right across the point of bending, you would probably
see -- under a magnifying glass -- wood fibers that have failed in
compression.

If you have ever broken small pieces of wood in half with your hands you
would have experienced this first hand. If you take that yardstick and bend
it until it starts to break, what happens? It does not just snap at once.

The outside part that is under tension will begin to splinter long before it
lets go. Then in order to break it, you instinctively bend it back in the
opposite direction and what happens? It makes a clean break on the top
surface -- the surface that was under compression -- while the bottom
surface continues to splinter.

This shows you just how much stronger the wood is in tension than in
compression. So even bending the stick and letting go befoer it breaks could
have caused compression failure on the top surface. The next time you bend
that stick in the opposite direction, there will be no strength in the top
part -- it will just let go.

That's exactly how sticks of wood can get damaged in transit. All it takes
is bending the stick enough to cause compression on the inside of the bend.
And you would never know by merely looking at it.

Idiot's comments about needing 10,000 pounds on top of the wood simply
illustrate to everyone what a loudmouth know-nothing he is.

All it takes is enough force to bend the plank more than you would normally
do. This does not have to be a lot of force. We are talking about small
planks less than an inch thick. You could easily cause compression failure
on small sticks of wood like this just by bending it forcefully with your
bare hands.

Is that the kind of massive pressure idiot is talking about?

The fact is that this type of damage can and does happen in shipment. It is
quite easy as my explanation should make clear. All that needs to happen is
for the board to be bent awkwardkly -- and this does not take a whole lot of
weight. A couple of humdred pounds acting on the end of a plank could be
enough to do it.

As to his other objection about modulus of rupture not being "enough" of a
measure to determine wood substitution, this is simply not true. This is the
most important measure of strength. Fbu (sometimes referred as jut Fu) is
the ultimate stress before failure in bending.

There are also measurements for stiffness, elasticity, strength in
compression and tension both paralell and perpendicular to the grain and a
few more. But the undisputed fact is that for structural members, Fbu is the
most important measurement.

If the substitute wood passes muster in this measurement, then it will pass
in all the others -- since these strength properties all tend to vary
proportionately across species. For example if pine is 15 percent weaker in
bending than spruce, it is also weaker by a similar amount in the other
strength measures.

In closing, I really have to register my utmost contempt at this pathetic
clown for the way in which he is conducting his attacks. He obviously knows
nothing, yet he has the brass to call into question factual material I have
presented which is 100 percent valid.

I challenge this complete moron to point out one mistake in the methodology
or math I have presented. I will bet dollars to donuts that he won't even
attempt it -- he wouldn't know where to start.


Regards to All (Except to Moron in NC)

Gordon Arnaut.




"Morgans" wrote in message
...

"Gordon Arnaut" wrote

If you disagree with something I said, then address it in civil terms as
I
have done when I disagreed with the other poster's point. There is no
excusable reason to launch into a personal attack and what I wrote
"crap."


I am normally a _very_ civil person, but I go off the deep end when
someone
makes a post retorting to have a command of subject matter, then displays
an
utter *lack* of grasp on the subject. People who know no better might
believe you, and commit a design change/substitution that kills them.
this
is big stuff, with life ending possibilities.

In order to have a compression fracture to take place, the wood has to be
compressed past the ultimate failure of the species, in compression, or if
it were bent, in rupture on the side of the board that is in the "low"
side
of the bend. How much force would be required would then depend on the
specifics of the size of the stock. I would dare to say, that the loads
required would be HUGE; it would be enough to crush the floor, and
suspension, and blow the tires of a UPS truck, if it were say, a spar, of
unremarkable size. That is not going to happen from having a box, or
boxes,
or even a V-8 engine sitting on it. How ridiculous!

If you purport to write as an expert, dispensing advise, you must be
prepared to take your lumps when you blow it.

You blew it.

Oh, by the way, pot, kettle, black. You seemed to do a pretty good job of
not addressing me in a civil manner.

I do not have a personality disorder, nor am I odiferous, nor am I an
idiot.
I was, however, bold enough to call you bluff on a subject you should not
be
writing about, if you are so far off base from knowing the basic causes of
this kind of failure in wood.

It seriously makes me wonder how far off base you are on the rest of the
figures and concepts you wrote about. I might suggest that other readers
also view the previous posts made by you with a *very* large grain of
salt.

Civil enough? If not, tough. Live with it.
--
Jim in NC