I have a 10 ft. high 3 inch diameter pole which I filled with concrete
(sand/topping mix). It took one and a half bags to fill the pipe.
I am doing this for a satellite dish antenna so the pole will be more stable
and not "wiggle".
Basketball mounting poles also have this done I am told....
Question: All that concrete is basically enclosed in the pipe and there is
just the opening at the top. How would the concrete cure? How long would it
take to cure? (Just curious...)
First of all I doubt that filling the pipe with concrete will have much
affect on the overall stiffness of the pole. The mount to the ground is
the most critical element.
The concrete will harden just fine. It's a chemical reaction taking
place, not drying in the typical sense. Remember concrete will set up
underwater if need be.
Bob Morrison, PE, SE
R L Morrison Engineering Co
When they built Hoover Dam they put cooling pipes through it
because of the heat buildup. When that section was set, they
pumped the pipe full of concrete and sealed it so sure it will set
up. And yes it will be stiffer. For a pipe to bend, a wall has
to collapse a fraction to full collapse. Full of concrete, that
action is curtailed.
I think the concrete stiffens the pole to better dampen out the
vibrations that can occur when the ball hits the rim. Also, alot of the
basketball pipes are multiple sections, so the concrete helps it act
like one structure instead of 3 pieces of pipe. I think the concrete is
a good idea for a satellite mount, as the wind can cause similar
vibrations and bending. I think you did good.
Why don't you just admit you weren't thinking when you wrote your
post, and move on. Lots of times I write stupid stuff too. Well, I'm
afraid I don't write things *that* stupid, but you get the idea. If
you try to defend a untenable position, it just gets worse.
It's really hard for me to understand how you could have said, "I
doubt that filling the pipe with concrete will have much affect on the
overall stiffness of the pole."
_Are you still standing by that statement?_
A pipe filled with concrete, a 3" pipe for this example, is much
stronger (and stiffer, if that's the term we want to use). Think about
it. For a pipe to fail, it has to deform. It can't deform easily if
it's filled with concrete. It's hard even to dent such a pipe with a
I could excuse you for not having experience with pipes filled with
concrete. But, considering you write "PE, SE" whenever you write your
name, and you advocate getting an engineer for almost everything, I
can't excuse you for missing the mechanics of how concrete would make
a pole stronger (or stiffer). In short, you're asking for it.
(||) Nehmo (||)
Yes I stand by the statement. You have assumed that the concrete remains
uncracked. If that is the case then one could rightly argue (as you have)
that the concrete helps make the pole stiffer. Once the concrete cracks
then the pole is at least theoretically no stiffer than an unfilled pole.
In reality this will depend on where the cracks in the concrete are
However, I should like to remind you that the first rule of concrete is,
"Concrete always cracks."
As someone else pointed out: the concrete adds mass and this will change
the natural period of vibration of the pole and may even give the apparent
feeling that the pole is stiffer.
Now you tell me which is easier to install: a 3-inch pipe with a 3/16"
wall that has to be filled with concrete into the 3" opening, or a 3-inch
pile with a 5/16" wall that doesn't have to be filled with concrete. I
know which I would choose.
Bob Morrison, PE, SE
R L Morrison Engineering Co
The argument as you present it is kind of silly. Of course if the
walls are thicker it will be stiffer, go all the way and say it is
solid 3" rod. The question was, would a pipe filled full of
concrete be stiffer and the answer is, yes of course. For a pipe
to bend it has to deform slightly. If it is full of concrete,
even cracked all over the place, it will resist deforming more.
All the Wal-Mart stores have pipes in front of the doors to stop a
car. They are filled with concrete to make them stiffer.
You also are confusing stiffness with strength. Buckling of the pipe is
more of an issue with strength than with stiffness. Stiffness is
relevant at all deflections from small to large, whereas, strength isn't
much of an issue until the load and thus deflection is rather large.
Bob is correct in saying that filling the pipe with concrete will have
very little affect on its stiffness. I will increase the strength if
the pipe is slender enough that buckling is the main failure mode.
They are not "completely different concepts"; they are related
concepts, particularly with the issue at hand. Now, what I said was
"A pipe filled with concrete, a 3" pipe for this example, is much
stronger (and stiffer, if that's the term we want to use)."
*I* specifically differentiated between the two terms, and I
parenthetically offered the term "stiffer" because that's the one he
used. I used "stronger" because that's easier to understand and I
believe that's what he meant anyway. But either term doesn't work. A
concrete-filled steel pipe is stronger and stiffer than one that is
It's absurd to argue otherwise.
I'm beginning to conclude you two have never been out in the field.
I've got a pipe filled with concrete two blocks from here. It's
stronger AND stiffer than the same pipe would be if it were empty.
Let's say it is used as a beam supported at both ends. A given amount
of weight in the center will make it deflect less than that same
weight on an empty pipe. Do you think otherwise?
The difference is so much, if I didn't know you both were humorless, I
would think you were joking.
"Concrete-Filled Steel Tube (CFT) Structural System is a completely
new system based on filling steel tubes with high-strength concrete.
The CFT Structural System promises excellent structural
characteristics; including rigidity, strength, deformation capacity,"
Concrete-Filled Steel Pole Goes Up in Southern Florida
One of the main advantages is the interaction between the steel tube
and concrete: local buckling of the steel tube is delayed by the
restraint of the concrete, and the strength of concrete is increased
by the confining effect of the steel tube.
There's more in this search: http://snipurl.com/1iiu5 ,
(||) Nehmo (||)
No, they are completely different. Stiffness is related to the slope of
the stress/strain relationship (elastic modulus) in its linear range.
Strength is how high the curve goes before failure. Not the same at
all. A material can be very stiff (glass), yet not strong (glass with a
small surface crack). A material can be very strong (spring steel), yet
not very stiff (spring steel).
Let's say you support the empty pipe as you say above (as a simply
supported beam) and measure its deflection in the center. Now stand the
pipe up, fill it with concrete and let it cure and then support it the
same way again and measure the deflection in the center. Which case do
you think will have greater deflection? And now explain why your
stiffer pipe has more deflection than the less stiff pipe that has no
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