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Old November 11th 03, 02:44 AM
McQualude
 
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Default Wood Question: Which is stronger, a round post or square post?

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.
--
McQualude

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Old November 11th 03, 02:50 AM
tecwhiz
 
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Default Wood Question: Which is stronger, a round post or square post?

the square post. more wood!
"McQualude" wrote in message
...
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.
--
McQualude



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Old November 11th 03, 02:52 AM
Rob Stokes
 
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Default Wood Question: Which is stronger, a round post or square post?

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
under compression.

Rob


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"McQualude" wrote in message
...
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.
--
McQualude



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Old November 11th 03, 03:25 AM
todd
 
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Default Wood Question: Which is stronger, a round post or square post?

"McQualude" wrote in message
...
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.
--
McQualude


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.

todd


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Old November 11th 03, 04:46 AM
Lawrence A. Ramsey
 
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Default Wood Question: Which is stronger, a round post or square post?

If it is made of bois de arc, it doesn't matter. It won't break.

On Mon, 10 Nov 2003 21:25:28 -0600, "todd"
wrote:

"McQualude" wrote in message
...
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.
--
McQualude


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.

todd




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Old November 11th 03, 06:09 AM
todd
 
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Default Wood Question: Which is stronger, a round post or square post?

"Rob Stokes" wrote in message
s.com...
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
under compression.

Rob


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.

todd
(gotta use that materials engineering education for something these days).


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Old November 11th 03, 06:44 AM
Steve Knight
 
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Default Wood Question: Which is stronger, a round post or square post?

On Tue, 11 Nov 2003 02:44:43 GMT, McQualude wrote:

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.


well if you measure corner to corner and the round post is the same in that
measurement it would be stronger. across the square post would be.

--
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Custom made wooden planes at reasonable prices
See http://www.knight-toolworks.com For prices and ordering instructions.
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Old November 11th 03, 06:50 AM
Lew Hodgett
 
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Default Wood Question: Which is stronger, a round post or square post?


McQualude writes:

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.


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.

HTH


--
Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
Visit: http://home.earthlink.net/~lewhodgett for Pictures


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Old November 11th 03, 04:19 PM
Fred the Red Shirt
 
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Default Wood Question: Which is stronger, a round post or square post?

McQualude wrote in message ...
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.

--

FF
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Old November 11th 03, 04:34 PM
Juergen Hannappel
 
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Default Wood Question: Which is stronger, a round post or square post?

McQualude writes:

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.


What dou you mean by "equivalent" in width? Same diameter as length
of side of the square? Then the square is stronger, because the
additional material in the corners adds considerably to the
geometrical moment of inertia.

If "equivalent" is meant that the same strength is reached there is no
difference...
--
Dr. Juergen Hannappel http://lisa2.physik.uni-bonn.de/~hannappe
Phone: +49 228 73 2447 FAX ... 7869
Physikalisches Institut der Uni Bonn Nussallee 12, D-53115 Bonn, Germany
CERN: Phone: +412276 76461 Fax: ..77930 Bat. 892-R-A13 CH-1211 Geneve 23


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