Yes it does (in this case). It may not be _efficient_ (strength /
weight will go down) but it isn't going to make it weaker (for a
simple solid post, placed vertically)
Die Gotterspammerung - Junkmail of the Gods
Depends on the load, but I'm assuming you mean under deflection. If so, the
square post is stronger as it has a larger surface area associated to the
top and bottom chords. This assumes all corners have been broken for stress
concentration relief. If you mean a load under tension, it's strictly a
matter of cross sectional area (assuming a consistent modulus of elasticity
across the section) thus the square section again would win...as it would
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Have to be a little careful with compression of a post. A lot depends on
the support conditions of the column, but you don't have to get a very
slender column (i.e. long in relation to cross-section) before buckling
becomes the primary failure mode. In this case, moment of intertia, not
cross-sectional area, will be the deciding factor. It still favors a square
cross-section over a round one, just not as much as the cross-sectional area
alone would lead you to believe.
(gotta use that materials engineering education for something these days).
As another poster indicated, assuming we're talking about bending, the
moment of intertia of a square cross-section is L^4/12. For a circular
cross-section, it's pi*D^4/64. I had to do the calculations three times to
convince myself that this is correct, but all things being equal, a square
post is 70% stronger than a round one when subjected to bending (this is
assuming that the diameter of the round post is equal to the sides of the
square cross-section). Keep in mind that the square has 27% more
cross-section to start with, though. Perhaps a fairer comparison would be
to compare equivalent cross-sectional areas. If equal cross-sectional areas
are assumed, the square cross-section is about 5% stronger.
>both made from the same wood and are both equivalent in width.
Under what conditions?
Compression loading as in a column?
The bending loading on a post at ground level that is buried a couple of
feet in the ground?
You have to define the problem first.
S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
He's asking valid questions. Fence posts, if braced, can be under
tension (rigid brace) or compression (wire brace). A long or high
fence needs to be braced. A corner post can be loaded in two
directions simultaneously. They can be bent as cantilevered out
of the ground or bent at the middle, braced at top and bottom.
We still haven't seen a decent definition of what "equivalent
width" means, only a vague statement.
email@example.com (Fred the Red Shirt) said:
No, that is the question. I gave the same answer you gave, but not
quite as clearly perhaps. I was hoping that someone would be able to
support it, because I have no proof and I don't think math will
answer this question.
(Fred the Red Shirt) said:
: >> I found this question in another group (misc.rural)...
: >> Which is stronger, a round post or square post? Assume the
: >> posts are both made from the same wood and are both equivalent
: >> in width.
: > Answering a different question, here but:
: > If you start with a tree trunk which is typically what you start
: > with for a fence post, it will be stronger if you leave it round
: > than if you square it up.
: No, that is the question. I gave the same answer you gave, but not
: quite as clearly perhaps. I was hoping that someone would be able to
: support it, because I have no proof and I don't think math will
: answer this question.
I would think that utilities would use square telephone poles if they were
stronger instead of
leaving them round. They spend a lot of money and resources on the poles they
push into the ground.
Apparently, you've never tried to drill a square hole in the ground. ;-)
From an engineering mechanics point of view, this is a very simple problem.
However, it probably breaks down for utilities on the basis of cost, i.e.,
it's just cheaper to get a round pole of similar strength than a square
pole. There are probably a hundred other reasons that make round poles
more workable (easier to climb with spikes, don't have to be oriented any
particular way, insulator bases are designed with round poles in mind, etc,
I think it boils down to economy and simplicity. You have
to start with a much larger tree to get a square pole with
the same strength of a round pole. And, you don't need to
send it through a sawmill or buy larger trees. Simplicity
depends on the type of wood. In the west, lots of poles are
lodgepole pine which grows straight with a long length that
changes very little in width.
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