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McQualude November 11th 03 03:44 AM

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

tecwhiz November 11th 03 03:50 AM

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




Rob Stokes November 11th 03 03:52 AM

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


--

Remove CC for email and please visit our web site:
http://www.robswoodworking.com



"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




todd November 11th 03 04:25 AM

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



Lawrence A. Ramsey November 11th 03 05:46 AM

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



todd November 11th 03 07:09 AM

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).



Steve Knight November 11th 03 07:44 AM

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.

--
Knight-Toolworks & Custom Planes
Custom made wooden planes at reasonable prices
See http://www.knight-toolworks.com For prices and ordering instructions.

Lew Hodgett November 11th 03 07:50 AM

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



Fred the Red Shirt November 11th 03 05:19 PM

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

Juergen Hannappel November 11th 03 05:34 PM

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

Scott Cramer November 11th 03 09:17 PM

Wood Question: Which is stronger, a round post or square post?
 
On 10 Nov 2003, todd spake unto rec.woodworking:

"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.


As another poster indicated, assuming we're talking about bending, the
moment of intertia of a square cross-section is L^4/12.


I had a moment of inertia shortly after finishing my lunch, but then
I went back to work.


Swingman November 11th 03 09:36 PM

Wood Question: Which is stronger, a round post or square post?
 
Then ask the question of the guy who got it to fit ... his IQ is obviously
higher.

--
www.e-woodshop.net
Last update: 9/21/03


"Milo" wrote in message
What if the round post is in a square hole?




Milo November 11th 03 09:44 PM

Wood Question: Which is stronger, a round post or square post?
 
What if the round post is in a square hole?

"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




McQualude November 11th 03 10:10 PM

Wood Question: Which is stronger, a round post or square post?
 
"tecwhiz" said:

the square post. more wood!


more does not always mean stronger

--
McQualude

McQualude November 11th 03 10:12 PM

Wood Question: Which is stronger, a round post or square post? [clarification, this about fence posts]
 
Don't make too many assumptions, this is a simple question.

It is about real world application of fence posts.
--
McQualude

McQualude November 11th 03 10:14 PM

Wood Question: Which is stronger, a round post or square post?
 
"Lew Hodgett" said:

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.


We're talking about fence posts.
--
McQualude

McQualude November 11th 03 10:15 PM

Wood Question: Which is stronger, a round post or square post?
 
(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.
--
McQualude

Bob Gramza November 11th 03 10:17 PM

Wood Question: Which is stronger, a round post or square post?
 

"McQualude" wrote in message ...
: (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.
: --
: McQualude

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.



McQualude November 11th 03 10:18 PM

Wood Question: Which is stronger, a round post or square post?
 
Juergen Hannappel said:

What dou you mean by "equivalent" in width?


So that no advantage is gained by having more wood. This is a simple
question.

If "equivalent" is meant that the same strength is reached there
is no difference...


I don't believe that. Fred answered the same way I did... that a post
turned from a tree would have greater strength than a square post.
--
McQualude

Bay Area Dave November 11th 03 10:22 PM

Wood Question: Which is stronger, a round post or square post?
 
maybe it's just easier to climb a round pole??

dave

Bob Gramza wrote:

"McQualude" wrote in message ...
: (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.
: --
: McQualude

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.




Juergen Hannappel November 11th 03 10:24 PM

Wood Question: Which is stronger, a round post or square post?
 
McQualude writes:


[...]

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.


The unchanged tree trunk is stronger because the parts that would get
cut away for squaring add most to its moment of inertia (as shown in
another posting here) and also leaving the wood intact with the
outside of the last growth ring as the exposed face makes it less
prone to rot than the open grain of a sawn surface.
If you need to have it thinner (or wand to make more than one post
from a lenth of tree) try not to saw byt to split.
--
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

todd November 12th 03 12:05 AM

Wood Question: Which is stronger, a round post or square post?
 
"Bob Gramza" wrote in
y.com:


"McQualude" wrote in message
...
: (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.
: --
: McQualude

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,
etc).

todd

Michael Daly November 12th 03 12:32 AM

Wood Question: Which is stronger, a round post or square post?
 
On 11-Nov-2003, McQualude wrote:

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.


We're talking about fence posts.


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.

Mike

George E. Cawthon November 12th 03 01:27 AM

Wood Question: Which is stronger, a round post or square post?
 


Bob Gramza wrote:

"McQualude" wrote in message ...
: (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.
: --
: McQualude

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.


You are kidding? Making a square pole would require taking
a large round pole and removing wood. Why would they spend
money to shave wood off and make the pole smaller and less
strong? You do know that the poles start out round, right?

George E. Cawthon November 12th 03 01:40 AM

Wood Question: Which is stronger, a round post or square post?
 


todd wrote:

"Bob Gramza" wrote in
y.com:


"McQualude" wrote in message
...
: (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.
: --
: McQualude

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,
etc).

todd


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.

Andy Dingley November 12th 03 01:42 AM

Wood Question: Which is stronger, a round post or square post?
 
On Tue, 11 Nov 2003 21:10:49 GMT, McQualude
wrote:

more does not always mean stronger


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

Juergen Hannappel November 12th 03 09:41 AM

Wood Question: Which is stronger, a round post or square post?
 
"George E. Cawthon" writes:


[...]

You are kidding? Making a square pole would require taking
a large round pole and removing wood. Why would they spend
money to shave wood off and make the pole smaller and less
strong? You do know that the poles start out round, right?


For a fence the choice is obvious: If the tree is thin: Make round
poles. If its to thick for that make pie shaped poles by splitting the
tree. If it's so thick that this still is no good idea use the
precious wood for something else.

--
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

Mortimer Schnerd, RN November 12th 03 11:25 AM

Wood Question: Which is stronger, a round post or square post?
 
Juergen Hannappel wrote:
"George E. Cawthon" writes:
For a fence the choice is obvious: If the tree is thin: Make round
poles. If its to thick for that make pie shaped poles by splitting the
tree. If it's so thick that this still is no good idea use the
precious wood for something else.



Round is the strongest shape in nature. It resists pressure equally in all
directions. That's why a submarine's hull is round in cross section.



--
Mortimer Schnerd, RN


http://www.mortimerschnerd.com



Dr. Know November 12th 03 12:09 PM

Wood Question: Which is stronger, a round post or square post?
 
On Wed, 12 Nov 2003 10:25:33 GMT, "Mortimer Schnerd, RN"
wrote:

Round is the strongest shape in nature. It resists pressure equally in all
directions. That's why a submarine's hull is round in cross section.


Which is important in keeping your fence posts from imploding. ;-)

Greg


Andy Dingley November 12th 03 12:58 PM

Wood Question: Which is stronger, a round post or square post?
 
On Wed, 12 Nov 2003 09:41:13 +0100, Juergen Hannappel
wrote:

For a fence the choice is obvious: If the tree is thin: Make round
poles. If its to thick for that make pie shaped poles by splitting the
tree.


One thing that hasn't been mentioned is "boxing the heart"

If you're going to cut a square post or beam from a tree, and you want
the strength to be comparable to a round post, then you must include
the pith roughly in the centre of the sawn post. Ask any timber
framer. (And also avoid species that fail from the pith). If it's
a beam with a large bending moment in one direction alone, then moving
the pith around may be justifiable (even moving it out of the beam
altogether), but this loses strength considerably in the other
directions.

If the round post is simply turned from a square post of equal face
width, then clearly the square post is stronger. But this is by a
negligible amount in most directions, and the weight of the post is
greater (by nearly a third).

If the round post is turned into a square, it also loses strength, but
this is likely to be more than simple geometry suggests, as the rings
are now no longer continuous.

--
Die Gotterspammerung - Junkmail of the Gods

Fred the Red Shirt November 12th 03 02:20 PM

Wood Question: Which is stronger, a round post or square post?
 
"George E. Cawthon" wrote in message ...
todd wrote:

"Bob Gramza" wrote in
y.com:


"McQualude" wrote in message
...
: (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.
: --


Of course math will answer the question although I suspect there is
some leg-pulling going on here. You want the fence post to be strong,
how, like so it doesn't fall over when a cow leans on the fence, right?

But you don't need math, you just need two brain cells to rub together.
If you start with a tree trunk that is round and square it then you
get a square post that is, at most, as wide accross the diagonals as
the diameter of the original tree. Now, suppose you want to reinforce
it. How would you do that? One way would be to nail extra boards to
all four sides of the post. OK, so take the four slabs you sawed off
to make it square and nail them back on.

The square beam might have a better strength to weight ratio but
who gives a damn? It's sitting in a hole in the ground, not on
your foot.

If you want to maximize the strength to weight ration then saw the
tree into lumber and construct box beams for your posts. Try sug-
gesting that over on misc.rural. Heck you can drill a little hole
in the side and they can double for birdhouses.

: McQualude

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. ;-)


What, you never heard of a designated dirt mortiser?


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,
etc).

todd


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.


Yes, if you start with a larger tree why not just stick it in
the ground instead of spending money to square it and make it weaker?

OK, they want the poles to be reasonably uniform in cross section,
but seriously, if you start with an almost round pole (tree trunk)
then the strongest symetrical pole you can get which will also
involve removing the least wood, will be a pole with a circular
cross section tangent to the inside of the trunk.

--

FF

P van Rijckevorsel November 12th 03 07:09 PM

Wood Question: Which is stronger, a round post or square post?
 
Fred the Red Shirt schreef
If you want to maximize the strength to weight ration then saw the
tree into lumber and construct box beams for your posts. Try sug-
gesting that over on misc.rural. Heck you can drill a little hole
in the side and they can double for birdhouses.


+ + +
Given the typical size of posts they had better be small birds.
Also pretty industrious to fill it all up to just below the hole!

Wouldn't a cross be stronger than a box?
(The birdhouse could be on top)
PvR




Mike Reed November 12th 03 07:28 PM

Wood Question: Which is stronger, a round post or square post? [clarification, this about fence posts]
 
The simple answer is round.

The reason is that for a given cross-sectional surface area, a square
has narrow spans and wide spans through the center. A circle only has
one span through the center (which is the diameter). If you don't know
what direction a load will be applied, then a circle gives you even
coverage in all directions, where a square is stronger along the
diagonals, but weaker than a circle of the same area, perpendicular to
the edges.

On the other hand, if you know where your load forces are likely to
come from, you could orient square posts to fight this, and may come
out ahead.

Another consideration is that trees conveniently grow with a
near-circular cross-section. So for any given tree, making a square
out of its trunk is going to weaken it by removing significant amounts
of material. Ideally a fence-builder will have a supply of
appopriately sized tree trunks, that have been debarked, depending on
the type of fence being built.

-Mike


-Mike

McQualude wrote in message ...
Don't make too many assumptions, this is a simple question.

It is about real world application of fence posts.


Kelly E Jones November 12th 03 09:07 PM

Wood Question: Which is stronger, a round post or square post? [clarification, this about fence posts]
 
In article ,
Mike Reed wrote:
The simple answer is round.

The reason is that for a given cross-sectional surface area, a square
has narrow spans and wide spans through the center. A circle only has
one span through the center (which is the diameter). If you don't know
what direction a load will be applied, then a circle gives you even
coverage in all directions, where a square is stronger along the
diagonals, but weaker than a circle of the same area, perpendicular to
the edges.


As intuitive as this may seem to you, it is, quite simply, very wrong.

A square, with sides of 1 in. and cross-sectional area of 1 in^2, has a
sectional modulus of 0.333 in^3.

A round, with diameter of 1.128 in, has a cross-sectional area of 1
in^2, and a sectional modulus of 0.141 in^2.

That means that in bending, a square is over twice as strong as a
round of the same cross-sectional area.

Have you noticed that, for example when building frames out of steel,
square tubing is much preferred over round tubing, despite the fact
that round tubing is much cheaper for a given size?

Intuition often misleads, engineering calculations rarely do.

Kelly



larry November 12th 03 10:54 PM

Wood Question: Which is stronger, a round post or square post? [clarification, this about fence posts]
 
McQualude wrote in message ...
Don't make too many assumptions, this is a simple question.

It is about real world application of fence posts.


It doesn't matter much wheather it is square or round. What matters is
the grain of the post. When a piece of lumber is sawn to a square
shape, the saw cuts across grain lines. This causes a weakness along
those lines. Traditionally round posts would have been split from the
log. This split would have followed the grain producing a perfectly
strong post. Since the splitting process would not produce square
timber and people were not interested in doing extra work, the posts
were either roughly rounded or left as they were split. If you are
wondering about buying round or square posts from your local lumber
yard I would say it is a matter of what you think looks good. Both
were sawn from the tree, the round one just had the corners knocked
off.

larry November 12th 03 11:53 PM

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.


Don't listen to all these engineers. Wood should be used based on its
properties, not their theories. Moment of inertia? If they ever
touched a real piece of wood I would be surprised.

George E. Cawthon November 13th 03 12:27 AM

Wood Question: Which is stronger, a round post or square post?
 


Juergen Hannappel wrote:

"George E. Cawthon" writes:

[...]

You are kidding? Making a square pole would require taking
a large round pole and removing wood. Why would they spend
money to shave wood off and make the pole smaller and less
strong? You do know that the poles start out round, right?


For a fence the choice is obvious: If the tree is thin: Make round
poles. If its to thick for that make pie shaped poles by splitting the
tree. If it's so thick that this still is no good idea use the
precious wood for something else.

--
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


Absolutely!

Fred the Red Shirt November 13th 03 01:18 AM

Wood Question: Which is stronger, a round post or square post?
 
"P van Rijckevorsel" wrote in message ...
Fred the Red Shirt schreef
If you want to maximize the strength to weight ration then saw the
tree into lumber and construct box beams for your posts. Try sug-
gesting that over on misc.rural. Heck you can drill a little hole
in the side and they can double for birdhouses.


+ + +
Given the typical size of posts they had better be small birds.
Also pretty industrious to fill it all up to just below the hole!


That would take a lot of crap indeed. OTOH we have been getting
a lot in this ng lately.

If the post was same weight as a standard post but constructed
as a hollow box beam then it'd at least be big enough for blubirds.


Wouldn't a cross be stronger than a box?
(The birdhouse could be on top)


No. A cruciform would not be stronger, again assuming the same weight.
Box beams concentrate material at the extreme fibers, the surfaces
at which the compressive and tensile forces will be maximum when
the beam bends. An I-beam would be better for a fence post than
a box, because the cow can only lean on it one way so you don't have
to worry much about bending parallel to the rails. THen you can
put the bird house on the top.

--

FF

Charles Spitzer November 13th 03 01:21 AM

Wood Question: Which is stronger, a round post or square post?
 

"todd" wrote in message
...
"Bob Gramza" wrote in
y.com:


"McQualude" wrote in message
...
: (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.
: --
: McQualude

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. ;-)


i'd like to see that mortiser

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,
etc).

todd




Kelly E Jones November 13th 03 02:06 AM

Wood Question: Which is stronger, a round post or square post?
 
In a fairly content-free post,
larry 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.


Don't listen to all these engineers. Wood should be used based on its
properties, not their theories. Moment of inertia? If they ever
touched a real piece of wood I would be surprised.


Wow, that's a pretty strong argument you've got there.

Kelly




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